H. BRIAN DICKENS
H. BRIAN DICKENS is head of the Codes and Standards Group, Division of Building Research, National Research Council of Canada, Ottawa 7, Ontario Canada. This paper has been prepared from the background papers listed at the end, and grateful acknowledgement is made to their authors
PUBLIC REGULATION of the design and construction of buildings is today a generally accepted part of the overall building process. Early building laws were concerned with the prevention of structural failure and collapse. It is recorded that the code of Hammurabi, prepared nearly 4000 years ago, stipulated that:" If a builder build a house for a man and do not make its construction firm, and the house which he has built collapse and cause the death of the owner of that house, that builder shall be put to death." Later, as communities prospered, regulations to safeguard against the spread of fire were issued. After the great fire of 1666, the London Building Act of 1668 empowered the city authorities to control building within its boundaries. Recently, regulations on sanitation, light and ventilation have been the subject of building controls. These three requirements Ä structural sufficiency, fire safety and protection against health hazards-today provide the basis of most laws that deal with the construction and use of buildings.
From their inception building regulations have been designed to protect the public. Traditionally they have been prepared by local authorities and based to a great extent on experience within the community. In general, this led to the development of a heterogeneous assortment of local ordinances that followed no consistent order, differed in many matters of detail and were frequently so specific in their restrictions that the introduction of new materials or methods of construction was made extremely difficult. Under such codes it can be difficult and even impossible to use wood or wood-based products to their full potential. It is essential, therefore, that these legislative and code aspects be considered in this overall review of the use of wood in house construction. This paper considers these aspects in the light of the material provided in the five background papers prepared specifically for this section of the Consultation. It presents a general review of the basic legislative and code approaches in current use and considers these in relation to their impact on the application of wood in house construction.
Ideally it may be argued that a person should be free to build how and where he likes. However, complete freedom in building can lead to chaotic situations and it is now generally accepted that the state must place limits on this freedom in the interests of the community as a whole. This is achieved through building and planning legislation.
Planning legislation controls the use of land and is designed to prevent any person from adversely affecting the convenience of others or the amenity of the neighbourhood. Building legislation is concerned with buildings and with protecting the health and safety of the occupants, and it is with these aspects and their impact on the use of wood in construction that this paper is primarily concerned.
It is important at the outset to distinguish clearly between the types of matters which should be covered under these two kinds of legislation -building and planning Many difficulties can be avoided if planning aspects such as zoning, density and height of buildings are kept out of building codes, which should restrict themselves to technological matters relating to the structural safety, fire protection and health aspects of the building
It should be noted, too, that the term building legislation refers to the establishment of an Act which forms the basis of the law and sets out the areas in which the Act shall apply. It may also encompass the appointment of a body responsible for the preparation and updating of the detailed regulations which are to be promulgated under the Act, the establishment of a mechanism for administering these regulations and the appointment of a body to act as referee or board of appeals. There may also be related legislation covering inspection and licensing of the building trades.
It is suggested that the control of building construction has three facets-tradition, law and science. Tradition and science should be recognized as methods of building control in addition to building regulations.
Building codes, or building regulations as they are sometimes called, are the technical instruments for implementing the Building Act. They form a purely technical document covering such matters as design standards, materials and their applications. When they are not directly incorporated in the building legislation, they can be more easily amended and capable of interpretation by the constituted building authority, leaving all arguments of law confined within the Building Act itself.
The new Scottish Building Act (1), introduced in 1959, is based on this principle of segregating those requirements which represent law and which remain unchanged for periods of time from those which are code or technical requirements, and which must keep pace with the trends of the industry and retain their flexibility for rapid change. This Scottish Act deals only with the legislative principles and the establishment and acceptance of regulations to be introduced separately. It establishes the machinery for administration, drafting and updating of the regulations, and provisions for appeals and modifications. The Scottish Building Regulations (2) to be used in conjunction with the Scottish Building Act were officially promulgated in 1963. Their enforcement, however, remains in the hands of local authorities.
The matter of uniform building regulations inevitably raises the question of national or local control of buildings. Those favouring the adoption of uniform building regulations on a national scale claim that such adoption will facilitate the work of builders and designers who operate in more than one area of jurisdiction, encourage the marketing of manufactured products on a national scale and promote the development of training courses to meet the needs of the building industry. It is also claimed that nationally uniform regulations will greatly encourage the development of standard testing. evaluation and certification procedures which should contribute to competitive production and general lowering of costs. National or even regional administration, with the regulatory district embracing a relatively large geographical area, should also lead to improvement in the organization and general quality of inspection and administration services. Against this must be weighed the added costs arising from centralizing these functions and the loss of flexibility that is inherent in the traditional system of operation.
One mechanism that has been used to promote uniform building regulations has been the development of so-called " model" codes. These are in evidence in the United States and are also the basis for the preparation of the National Building Code of Canada (3). Such codes are advisory only until legally adopted for use by appropriate legislation. Canadian experience will be summarized here, not as representing any ideal solution, but because it does illustrate the way in which the model code approach may be used to promote uniformity of building regulations within a country.
NATIONAL BUILDING CODE OF CANADA
The National Building Code of Canada was first published in 1941 under the joint sponsorship of the National Research Council and the Department of Finance. Although only advisory it was written so that it could be adopted or enacted by any municipality in Canada as its own building bylaw by passage of the necessary legislation. The National Research Council assumed full sponsorship of the Code in 1948, and in that same year established a special Associate Committee on the National Building Code to be responsible for keeping the Code up to date. Subsequent editions have been published in 1953, 1960, 1965 and 1970, with future editions to be introduced at five-yearly intervals and annual revisions issued at the beginning of each calendar year. Today this national set of building regulations is in use in one form or another through voluntary local adoption by over 70 percent of the population of Canada. In addition, several provincial governments are currently considering the adoption of the National Code as a mandatory code for all building within their provincial boundaries. It should not be too long, therefore, before the regulation of almost all building throughout Canada will be based on this same fundamental document.
One of the strengths of the model code approach has been its ability to arrange for the necessary expertise to be applied to the preparation and updating of the code. In the case of the Canadian Code, the Associate Committee responsible for its preparation and regular revision is composed of leading members of the construction industry in all its phases, drawn from all parts of Canada. The members serve voluntarily, each appointed as an individual and not as a representative of any special group, for a three-year term. The Associate Committee determines all policies for the Code and, with the assistance of the staff of the National Research Council, is directly responsible for its many services. Specialist technical committees appointed by the Associate Committee are charged with the detailed task of preparing the technical content of the Code, which must come before the Associate Committee for final approval and implementation. Suggestions for improvement or change are regularly solicited from anyone interested enough to submit them. All are carefully considered and drafts of new or revised documents are always made available for public comment before issue. In these and similar ways the National Building Code of Canada has steadily achieved the status of a truly national document, a continuing tribute to the voluntary efforts of architects, engineers, contractors, house builders, public officials, trade unionists, manufacturers and others comprising the 250 individuals involved in the work leading to the preparation of each edition.
The application of a single code to a country the size of Canada is made possible by drafting it so that specific requirements which depend on climate are related to the basic climatic data for the locality in question. These climatic data are contained in a special Suplement to the Code, one of the many services provided in support of the Code itself. The Code is also produced in a short form which regulates buildings up to three storeys in height and 6 000 square feet on any one floor. This shortened document has received wide acceptance among the smaller municipalities, since it covers most of the buildings with which they are concerned. A similar approach has been used by the Building Research Station in the United Kingdom to produce a set of model regulations for small buildings (4). These are proposed as a guide to legislation for the developing countries.
Coupled with the question of the mechanism to be used in preparing building regulations is the equally important question of the form they should take.
In the past nearly all regulations were written in the form of brief specifications, stating what materials could be used and how. For example, bylaws made under the London Building Act of 1668 laid down that party walls between buildings should be of burnt brick laid in mortar, and specified the thickness of the walls for different heights. These rules were intended to ensure that walls were structurally safe and prevent the spread of fire from one building to another, and they served their purpose without major difficulties for 200 years because brick was the only material available. However, this type of regulation makes no provision for the acceptance of new materials and when concrete was introduced as a substitute for brick the regulation was unable to accommodate it.
Modern theory is that controls should be phrased in such a way that designer and builder are given freedom to use any material or design technique they wish, provided the completed building offers the necessary protection to the occupants with respect to structural sufficiency, fire prevention and health hazards, these being the three foundation stones on which all building regulations must rest. The difficulty lies in devising suitable regulatory mechanisms to achieve this end.
Most current codes attempt to meet this problem by incorporating what is popularly called an escape clause. In the Canadian Code, for example, there is a clause that specifically empowers the authority having jurisdiction to accept new methods and materials where their suitability has been established by test or experience or through accepted engineering analysis. It recognizes as a basic principle that no form of construction should be excluded as long as it meets the intent of the Code. The principle is, of course, much more difficult to implement than to state, since its application generally depends on the availability of adequate performance criteria against which to assess the proposed construction. Such criteria are the subject of an intensive study currently under way at the National Bureau of Standards in the United States as part of the " Operation Breakthrough" programme of the Department of Housing and Urban Development.
PERFORMANCE CRITERIA
It is in the development of such performance criteria that practical difficulties arise. The evaluation techniques or the methods of measuring criteria are the crux of the problem. To be usable a performance type of regulation must state in precise and measurable terms the result which must be achieved. This will require that it be associated with an adequate test method. It is meaningless to make a statement of technical requirements for a building if one cannot determine whether a material or method of construction meets these requirements.
It is important to distinguish clearly between the two essential elements in the performance approach. One is the need to establish standard test conditions and method of measurement on which predictions of in-service performance can be based. This is currently receiving increased attention by national standards writing organizations in several countries, including the American Society for Testing and Materials in the United States, the British Standards Institution in the United Kingdom, the Canadian Standards Association in Canada, and also by the International Standards Organization. The other element is the prediction of performance in terms of the information obtained from such tests and. ultimately, as in the case of codes, the setting of minimum criteria for each specified end use. The adequacy of the performance test approach is limited by the ability to anticipate the conditions which will exist in actual practice, and to simulate in the test those which represent a suitable limiting or design condition for evaluation purposes.
Despite these difficulties there is a strong trend toward the use of performance standards in modern codes as one of the most suitable ways of allowing the use of a material or system to its full potential. Assessment against such performance standards is particularly important in the case of new or untried materials, or methods of construction which might otherwise face considerable difficulty in gaining acceptance. Many materials have been discriminated against because of a lack of understanding of their actual performance in service. Wood is certainly one of those materials which can gain from performance codes, since there are many instances where concern over the fact that it is combustible has resulted in arbitrary restrictions being placed on its use in buildings. Although wood has limitations, one of which relates to its performance in fire, recent developments indicate that building regulations based more on the performance approach and utilizing the latest technical information can avoid some of these specific restrictions and facilitate the use of wood in construction without reducing the level of safety.
A technique that has been used to permit the framing of regulations in the functional or performance form. and still provide practical guidance to the designer, builder or enforcing authority, is through the development of deemed-to-satisfy clauses. The mandatory requirement with which the owner must comply is expressed in performance or functional terms. The deemed-to-satisfy clause provides a detailed description of construction that may be used to satisfy the requirement. It may take the form of a brief specification, or reference to another document-such as a code -of practice-which is published separately. In this way traditional methods and materials cease to be mandatory but are recognized by being given as examples of compliance with the required standards of performance. This has obvious advantages in developing countries since the deemed-to-satisfy clauses can be enforced by building inspectors with only an artisan's training, whereas the assessment of construction against performance criteria frequently requires professionally trained personnel.
UNIFORM EVALUATION AND INTERPRETATION
Uniform application of building regulations, through uniform interpretations and assessment of new forms of construction by the local enforcing authority, can be greatly assisted by the establishing of performance type requirements and some form of centralized or national evaluation scheme. The system known as Agrement, originally developed in France and later extended to other European countries, including the United Kingdom, provides one example. South Africa is developing a similar scheme.
It permits the proponent of a new material or method of construction to seek evaluation by the Agrement board, leading to the issuing of an Agrément certificate which states, in effect, that the new material or method of construction is suitable for use in a certain way for certain purposes. The certificate is normally issued for a limited period only, to serve until such time as the item in question can be included in a recognized standard. The certificate is generally acceptable to local authorities as evidence that the new material or method when used as described can be deemed to satisfy the requirements of the regulations.
As an alternative to the more comprehensive Agrément approach, two model code groups in the United States, the Building Officials Conference of America and the International Conference of Building Officials, each developed a central evaluation scheme as part of their code service to assist the enforcing authority to determine whether a particular material, system or component not specifically covered by the detailed code requirements can be deemed to satisfy the intent of the code. Each group issues its findings in the form of a published report in which the product is fully described, and the specific code uses for which it is accepted are clearly stated. These reports are called recommendations, since the final approval must always remain with the authority having jurisdiction.
This central evaluation, based on the best information available, can do much to maximize the effective use of wood and, indeed, of all building materials, in house construction.
Building legislation and related building regulations or codes can markedly affect the applications of timber in building. The subject is too complex, however, to permit more than a cursory review of the overall problem, even in the more limited field of housing. Some relevant comparative studies were undertaken recently by the Timber Committee of the Economic Commission for Europe, but the results were not available in time to be referenced in this paper. In the absence of such data, this paper will attempt to establish some broad generalizations on the effect of statutory controls on timber use through reference to practices in specific countries as reflected in the background papers provided for this session.
Most building code restrictions on the use of wood arise from regulations designed to provide for structural stability, durability and protection from fire. These aspects will be discussed in some detail and illustrated with examples of typical code requirements where appropriate.
STRUCTURAL STABILITY
There are few questions raised concerning the adequacy of timber with regard to structural safety in buildings. Most regulations make reference to recognized standards or codes of practice such as the Code of recommended practice for engineering design in timber of the Canadian Standards Association (5), or the Code of practice for the structural use of timber of the British Standards Institution (6), which are deemed to satisfy the functional requirements for safety in respect of materials and methods of design. As Dobson (7) illustrates by reference to South African experience, such documents, to be a suitable base for building regulations, should relate to the kinds of timber that are readily available to the builder.
CANADIAN APPROACH TO STRUCTURAL STABILITY
The National Building Code of Canada offers two approaches with regard to structural requirements. Structural members may be designed in accordance with standard engineering practice to withstand specified design loads, or they may be constructed in accordance with requirements which specify such details as allowable member sizes, spacings, spans and fasteners. The requirements for conventional wood-frame construction apply to structures in which the wood members usually consist of nominal 2-inch lumber spaced up to 24 inches apart. The Code also covers other wood systems including plank frame walls and post and beam construction. The former is constructed of vertical load-bearing planks with horizontal filler planks in between. The latter sys. tem differs from conventional frame construction in that the primary load-bearing members are spaced more than 24 inches apart and are larger in size. The detailed construction requirements are, in effect, the deemed-to-satisfy clauses, since they contain sufficient information to permit the structural detailing of small residential buildings without the necessity of engineering or architectural services.
An important feature which facilitates this approach has been the development of span tables for floor and roof framing members and for beams. These are prepared for various conditions of loading and for a wide variety of timber species utilizing the grade marking system now well established on a national basis in Canada. The system is operated under a nongovernmental but nationally organized board through which grading agencies are controlled and licensed. Before the board grants such a licence it investigates carefully to ensure that the graders are qualified for the work and that each grading agency can maintain supervision of its graders. As an additional safeguard, a check-grading service has been established to periodically verify the work of the graders and ensure that the agencies are maintaining satisfactory standards. The grade marks identify each piece as to species, grade, the rules under which it was graded, and the producing mill or grader identified by number. These grade marks are placed on dimension lumber, boards for sheathings, subflooring and roof sheathing, and finished flooring, in such a position that they will be visible after framing but before cladding has been applied.
Another national board, similar in operation to the lumber grade marking board, has been established to oversee the quality of manufacture of structural glued-laminated timber. To be qualified by the board each plant must employ certain equipment and personnel and pass regular inspections to ensure that manufacturing and quality control procedures are up to standard. Each qualified laminator may attach a suitable label to his product and may also provide a certificate attesting to its manufacture in accordance with the national standard.
Quality control of structural glued-laminated timber by this means, and of sawn lumber through grade marking, coupled with an increasing awareness of developments in timber technology and recognition in national codes and standards, can do much to facilitate more widespread and effective use of wood in construction. The importance of research support on a national basis is reflected in the fact that the data used in preparing Canadian Code criteria for timber are based almost completely on information developed in government laboratories and made available for use by the public. Through close liaison with similar research and code writing agencies in the United States, design standards for timber are now nearly uniform in North America. This is most desirable in the light of today's highly mobile population and the not uncommon situation of consulting firms undertaking designs for construction in distant locations.
Paralleling these developments have been some additional refinements of the Canadian regulations which influence the use of timber in house construction. The development of a performance test requirement for wood roof trusses is one. When roof trusses were first used in houses, they had to be designed in accordance with recognized timber engineering methods and this resulted in structures much stronger than the more traditional type of roof framing. Since this latter framing had provided satisfactory performance for many years, it seemed reasonable to use it in establishing a level of acceptability for trusses. However, the strength of traditional house roofs was not known and so an extensive research programme had to be undertaken. From this have developed a set of design criteria and a corresponding test method which now form the basis for the acceptance of practically all residential timber truss systems used in Canada. This offers several advantages. It allows assessment on the basis of simple tests, it ensures roofs at least as strong as conventional roofs and it encourages more efficient use of both lumber and fasteners. Another important study has been in relation to snow loads on roofs. Observations of snow loads on a large number of roofs across Canada over a period of several years have led to a reduction of 25 percent in roof design loads for houses, with corresponding savings in construction costs.
A further area where research studies have allowed code requirements to be more liberal is in relation to wall sheathing and bracing. It has been traditional in the construction of exterior wood-frame walls to require corner bracing or sheathing to resist racking forces due to wind. These requirements have now been eliminated and sheathing is specified only where needed for the support or attachment of the siding material. This has resulted in part from racking tests on wall panels which indicate that in most cases the interior finishing material alone provides greater resistance to racking than does traditional sheathing or bracing. Tests have shown, for example, that lath or plaster contributes almost four times as much to rigidity as do bracing and horizontally applied sheathing. Other examples of cost saving changes to code requirements include the elimination of cross-bridging in timber floors and wider stud spacing for timber partitions.
All these changes have come about through a critical review of requirements based on new information. The continuing interaction between building code committees and national building research studies has proved a valuable stimulant to code improvement, and instrumental in originating new research by pinpointing areas in which additional information is required. Such refinements in code requirements, based on the best technical information available, supported through research and often stimulated by informed public comment, are essential if codes are not to hinder the efficient use of materials and the application of modern technology.
DURABILITY - PROTECTION FROM MOISTURE
Durability of timber and protection from moisture are closely linked. Fungus growth results in rotting and is associated with damp or wet conditions and lack of ventilation. Insect attack is another problem, related to climatic conditions and to type of both insect and wood.
Most codes provide for protection of timber from moisture through flashing, caulking, ventilation, or separation of the timber from the ground or other sources of moisture. To guard against insect attack some form of preservative treatment is generally required and, in the case of termites, termite shields designed to prevent access to the structure from the ground via the foundation and plumbing, or impregnation of the soil around the building with poisonous chemicals, are often specified.
Generally speaking, durability requirements in codes do not place onerous restrictions on the use of timber in construction, particularly where the performance characteristics and relative durabilities of the local species of timber have been established. The importance of such background studies is reflected in the paper by Dobson (7) which comments on the properties of certain South African timbers and the need to develop an understanding of their performance before their use can be properly promoted. Consumer resistance to a nontraditional method of construction is natural and the resistance of both the public and the building authority may be strengthened by the publicity given to even one failure. The development of timber standards or codes of practice based on well-documented information on the properties of local species is therefore important.
FIRE PROTECTION
The danger of fire has been a major incentive toward the enactment of building legislation. This has led many code-writing authorities to incorporate in their building regulations specific provisions that can be quite limiting as far as the use of timber is concerned.
During the last decade fire research has increased considerably all over the world in an attempt to place design for fire safety on a basis more closely approaching that of structural design, for which there exists an extensive background of research, a large body of codified knowledge and an active and competent group of specialist consultants. The performance required may be established by a regulatory code and the actual design left to the specialist practitioner. In fact, maximum freedom in design becomes possible only when safety can be included and adequately treated as a design consideration.
Although the situation is improving, design for fire safety is still at an elementary stage of development compared with design for structural safety. There is no real choice at present but to accept a highly regulated approach in building codes where potential fire hazards exist. This makes it particularly important that building regulations be based on information from fire research studies. Such studies have already led to the inclusion of performance requirements in the national building regulations of some countries, including Sweden, Canada and the United Kingdom, and these in turn permit much greater freedom in the use of timber products than was possible under earlier regulations.
These improvements in current codes with respect to fire safety requirements can be best understood when considered against the background of modern fire protection technology. In the following discussion of these developments emphasis is given to the Canadian approach, and to some extent the Swedish, based on information provided in the background papers by Hansen (21) and Odeen (23). Both countries have large timber resources and a long tradition of timber construction. Where reference to standard fire tests is included these apply for the most part to the tests specified by the National Building Code of Canada.
COMBUSTIBILITY OF CONSTRUCTIONS
The regulation of the use of combustible materials in building construction has been imposed for many years in building codes as a contribution to fire safety (8, 9). The requirements may be specific and limit the use of combustible materials to specific locations within a building, or be more general and apply to the construction as a whole. Most codes recognize two basic types of construction-combustible and noncombustible-and generally require the latter to be used for buildings exceeding certain size limits.
The Canadian National Code defines noncombustible construction as being made up of noncombustible materials such as steel, concrete or masonry, but with certain combustible elements permitted. These latter include furring or nailing strips for the attachment of interior walls, ceiling or floor finishes, and millwork such as interior trim, doors, door frames and certain arrangements of sash and frames for wood-frame windows. Such construction may also have combustible wall, ceiling and floor finishes, providing the wall and ceiling finishes are not more than 1 inch thick and meet specified flame" spread ratings. The use of nonload-bearing wood-frame partitions is permitted in buildings of noncombustible construction provided the partitions are located within dwelling units and are covered on both sides with noncombustible materials.
Combustible construction in terms of the Canadian Code includes conventional light frame, heavy timber, plank frame and post and beam construction, as well as composite, which incorporates combustible materials in excess of that permitted for noncombustible construction.
The Code requires that beyond a certain size buildings must be of noncombustible construction. It limits the use of combustible construction for housing to a height of three storeys and places further limitations on the maximum area per floor in relation to the number of streets on which a building faces and whether or not it is sprinklered, as indicated in Table 1.
These size limits are for the purpose of assisting fire fighting and occupant rescue, the assumption being that increased street access or fewer storeys will permit larger floor areas for a given type of construction. The Canadian Code requires that floor assemblies in buildings permitted to be of combustible construction, other than floors within dwelling units and detached, semidetached and row houses, must have a fire resistance rating of at least 45 minutes. Residential buildings which exceed size limits for combustible construction are required to be of noncombustible construction and, in addition, must provide a minimum fire resistance in the structural members of from one to two hours, depending on the height and area of the building
TABLE 1.- MAXIMUM SIZE OF COMBUSTIBLE BUILDINGS
|
Maximum height, storeys |
Maximum floor area1 |
||
|
Facing 1 street |
Facing 2 streets |
Facing 3 streets |
|
|
Square feet |
|||
|
1 |
12 000 |
15 000 |
18 000 |
|
2 |
9000 |
11 200 |
13 500 |
|
3 |
6000 |
7500 |
9000 |
SOURCE: National Building Code of Canada 1970.
¹Areas may be doubled where the building is sprinklered.
COMPARTMENTATION
A major factor that will contribute to the reduction of fire risk in a building is the use of fire resistant construction to separate a building into fire resistant compartments. The fire resistance or fire endurance of the enclosing elements of a compartment is determined by subjecting the assembly to standard fire conditions in a test furnace (10).
It is generally defined as the time (in hours) during which the test assembly continues to satisfy the test criteria of stability, integrity and thermal insulation. These are reflected in the three basic types of failure recognized in the test: collapse; formation of cracks allowing the passage of flame and hot gases; temperature rise on the unexposed face.
Not all the criteria need to be satisfied in all situations Ä the necessary criteria depend on the nature of the structural element and the function it is designed to perform. Load-bearing elements such as beams and columns need only satisfy the criterion for stability. Walls and floors, however, may be required to meet all three criteria. In testing the fire resistance of doors or other closure devices the temperature rise criterion is waived, but the door or other device must remain in place during the test. The omission of the temperature rise requirement is based on the fact that material would not normally be placed next to a fire door through which people or goods must pass. It is considered sufficient that this element of construction resist the passage of flames for a specified period of time. Today many countries have their own standard fire resistance tests and, although these may differ somewhat in detail. they have been of considerable importance to the development of more rational criteria in building codes.
Modern codes require constructions to have varying degrees of fire resistance, depending on the quantity of combustible material normally found in the occupancy for which the building is designed. The quantity of combustible material per square foot of floor area is commonly referred to as the fire load. Studies carried out to establish the relationship between fire resistance and fire load indicated that a construction with a l-hour fire resistance (based on the standard test) will withstand a burnout where the fire load of the space is equivalent to that of 10 pounds of wood per square foot of floor area; correspondingly, a construction having a 2-hour fire resistance will withstand a burnout when the fire load of the space is 20 pounds of wood per square foot.
Thus, a building with a high fire load will require a higher fire resistance rating than a building with a low fire load.
In the case of tall buildings, although this same principle is recognized, an additional safety factor against catastrophic collapse is introduced by requiring greater fire resistance ratings of structural elements than required for low buildings, even though the fire load may be the same.
Fire-rated construction should not be confused with noncombustible construction, which may or may not have the requisite degree of fire resistance for a particular situation. It is also important to distinguish between fire resistance and fire separation. Fire resistance or fire endurance refers to a quality of the construction of a building component and is characterized by its ability to satisfy requirements relating to temperature rise, flame penetration and structural stability in accordance with a standard fire test. The term fire separation indicates only that the construction must serve as a physical barrier to the spread of fire from one compartment to another. It may or may not be required to have a fire resistance rating.
The Canadian Code requires that dwelling units in a residential building must be separated from each other and from public corridors or other public areas in the building by fire separations. In buildings of combustible construction this separation must have at least a 45-minute fire resistance rating where the unit contains one floor level, and a 1-hour fire rating where the unit contains more than one level. Fire separations must also be provided around public exit stairs (45-minute rating in combustible construction). storage rooms, machinery rooms, boiler rooms and furnace rooms (I hour), and around incinerator rooms (2 hours) where these serve more than one dwelling unit. Where a door opening occurs in a 45-minute separation permitted to be of combustible construction, a 1 3/4-inch solid wood door is acceptable as a closure but where a l-hour separation is required in other locations, a 45-minute rated door is required (11). Where a 2-hour separation is called for, the door must have a I '/2-hour rating.
FIRE RESISTANCE OF WOOD CONSTRUCTION
Wood exposed to fire is gradually destroyed by charring at a rate of about one fortieth of an inch per minute.
There are two ways by which a measure of fire resistance can be provided in wood assemblies. One is to provide assemblies of substantial size. Economics are an important consideration here, since defects such as knots and discontinuities caused by mechanical fasteners in built-up members can reduce the fire rating markedly and solid timber sections of high quality are expensive. This has led to increased interest in glued-laminated timber elements which have been shown by test to provide fire resistance equivalent to that expected of solid sections.
The other method is to add a protective covering or membrane to the wood structure. For example, an increase of about 15 minutes in the rating of solid wood walls or floors can be obtained by the application of 1/2-inch gypsum board to the side exposed to the fire. This is further increased if the special fire-rated gypsum board is used. The addition of a membrane is even more important in light frame construction, since tests have shown that unprotected wood framing will fail structurally within about 10 minutes for ceilings and 20 minutes for uninsulated walls when exposed to the standard fire test. The time during which the membrane remains in place is therefore of great significance in the fire resistance of an assembly. This applies to floor-ceiling assemblies as well as to walls. Failure occurs more commonly by collapse than by rise of temperature on the unexposed face and can occur rather quickly once the protection of the membrane has been lost. Consequently, the nature of the membrane and its method of fastening are of great importance.
A procedure has been developed to allow the calculation of the fire resistance of light frame constructions by assigning values to the contribution of the membrane exposed to the fire, the contribution of the frame and the contribution of additional insulation or reinforcement. These assigned values, based on test data and judgement, make it possible to assess the fire resistance of a variety of assemblies without the necessity of individual tests. This calculation procedure, as well as test ratings for typical wall and floor constructions. is provided in a Supplement to the National Building Code of Canada entitled Fire resistance ratings (12). These indicate a variety of partition and exterior wall constructions, as well as floor-ceiling assemblies of wood frame, which can provide 45-minute and 1-hour fire resistance ratings.
The fire ratings for interior walls or partitions assume that a fire can occur on either side of the wall. The ratings for exterior walls assume that it occurs within the building. In the case of floor-ceiling combinations the fire is assumed to occur on the underside of the assembly.
An important fire safety provision of the Canadian Code relating to wood-frame construction requires that fire stops be installed at floor, ceiling and roof levels to cut off concealed spaces between storeys and between the top storey and roof space to prevent the transfer of fire and hot gases to other parts of the building. Such fire stops usually consist of nominal 2-inch lumber. In the case of platform frame construction, the top and bottom wall plates serve this function.
SURFACE BURNING CHARACTERISTICS
The surface burning characteristics of an interior lining material can influence the time available for escape and the rate of development of a fire in a compartment. The most significant characteristics are flame spread and the production of smoke and gases. Although the concept of flame spread is quite simple, the real situation is not, and it is not an easy matter to develop a standard test to evaluate the role of interior linings in actual situations. Three flame spread tests have been developed in the North American continent. Colloquially they are known as the large tunnel, radiant panel and small tunnel tests.
The large tunnel test is at present the only one recognized by the Canadian Code. The flame spread rating uses a scale based on 100 for red oak and 0 for asbestos (13).
The Canadian Code requires that the flame spread rating of walls and ceilings of all residential buildings' including single family houses, be not more than 150 on this scale. In the case of public exits and public corridors, there are additional restrictions. For example, exits such as stairways serving more than one dwelling unit must have at least 90 percent of the wall and ceiling surfaces with a flame spread rating of not more than 25. Where noncombustible construction is required, combustible ceiling and wall finishes may be used, provided the flame spread ratings do not exceed 25 for the former and 150 for the latter. This rating must apply throughout the materials and not just for the surface. More restrictive ratings are required for exits and public corridors in noncombustible constructions.
When determined by the large tunnel test, untreated lumber varies from 60 to 215 and when treated with a fire retardant coating varies from 10 to 25. Untreated plywood varies from 100 for Douglas fir to 250 for thin prefinished decorative plywoods. Treated Douglas fir plywood varies from 10 to 25. Fire retardant coatings applied to Douglas fir can reduce its flame spread from 100 to between 10 and 35. Gypsum wallboard has a flame spread of 25 or less.
In the United Kingdom, the surface burning characteristics of a material are assessed by the surface spread of flame test. The British Standards Institution test (14) classifies materials in four grades, class I being the slowest and class 4 the most rapid burning Untreated lumber in its natural state and products made from it, such as plywood, particle board and fibre insulating board, achieve a class 3 or 4 grading in this test which renders them unsuitable for use in many situations covered by the British building regulations. The behaviour of timber can, however, be improved to class I by the application of fire retardant treatments, either as surface coatings or by impregnation. The permanence of the protection offered by either method, however, is questionable.
Sweden uses another test, the Swedish box test, on the basis of which surface finishes of walls and ceilings are classified as fireproof (class 1) or fire retardant (class 2). This box test is considered to offer advantages over open type tests by establishing more realistic conditions for evaluation purposes.
The variety of methods reflects the difficulties encountered in formulating test situations to simulate limiting or design conditions. Tests will continue to be improved and, it is hoped, agreed upon internationally as knowledge increases and the conditions existing during actual fires are more precisely defined.
RADIATION AND SPATIAL SEPARATION OF BUILDINGS
As noted, the Canadian Code requires a certain degree of fire resistance to provide structural integrity in the event of fire, and permits buildings up to a certain size to be of combustible construction. are also requirements in relation to the proximity of the building to the lot line that impose additional restrictions on exterior walls. These restrictions affect only the exterior walls and not the entire building.
Distances between buildings must be such as to ensure that a fire in one is unlikely to spread to an adjacent building. The principal cause of such fire spread is radiation. and it is now generally accepted that if radiation is to be controlled it must be reduced to a level that will prevent ignition of a building clad with combustible materials that is directly in its path. The hazard of radiation depends on the temperature of the fire, the size and shape of the radiating surface and the distance between the burning building and the one it threatens. There is conflict between the need or desire for windows, and the fact that the critical part of a building involving the transfer of radiation is the window.
Recognizing this, the Canadian Code has incorporated extensive tables to regulate the percentage of openings permitted in walls in relation to the distance from a property line. For buildings up to three storeys in height and not more than 6000 square feet on any floor, the percentage of openings shown in Table 2 may be used.
It will be noted that unprotected openings are not permitted in walls that are less than 4 feet from a property line. The Canadian Code contains several additional requirements that can affect the acceptability of wood construction as follows:
1. Where a detached, semidetached or row house is located less than 4 feet from a property line, the wall must have a fire resistance rating of at least 45 minutes. If the wall is less than 2 feet from the property line, it must have noncombustible cladding as well.2. For residential buildings other than detached, semi detached and row houses, the requirements are somewhat more restrictive, being related to the percentage of allowable openings for the various specified limiting distances as indicated below:
For permitted openings of 10 percent or less, the wall must be of noncombustible construction having at least a l-hour fire resistance rating.For openings of 11 to 25 percent, the wall may be of combustible construction having a 1-hour fire
resistance rating. resistance rating although noncombustible cladding is required.
For openings of 26 to 100 percent, the only restriction is that the wall shall have a 45-minute fire resistance rating.
For limiting distances greater than those shown in Table 2, there is no requirement for fire resistance or non-combustibility.
TABLE 2. - MAXIMUM PERCENTAGE OF UNPROTECTED OPENINGS IN EXTERIOR WALLS¹
|
Maximum area of building face³ |
Limiting distance² |
||||||||
|
Up to 4 ft |
4 ft |
6 ft |
8 ft |
10 ft |
15 ft |
20 ft |
30ft |
50 ft |
|
|
Percent |
|||||||||
|
Up to 300 sq ft |
0 |
12 |
17 |
25 |
35 |
68 |
100 |
- |
- |
|
300 to 399 sq ft |
0 |
11 |
15 |
21 |
29 |
54 |
89 |
100 |
- |
|
400 to 499 sq ft |
0 |
11 |
14 |
19 |
25 |
45 |
73 |
100 |
- |
|
500 to 999 sq ft |
0 |
9 |
10 |
14 |
17 |
28 |
43 |
88 |
100 |
|
Over 999 sq ft |
0 |
6 |
7 |
10 |
12 |
17 |
23 |
41 |
100 |
OURCE: National Building Code of Canada 1970.
¹Amount of openings shown in the table may be increased if the limiting distance does not exceed the square root of the total window area in the building face. -2 Limiting distance is measured at right angles from each building face toward a property line, or an assumed line between two buildings on the same property. or to a centre line of a street or lane.-3 The area of a building face is calculated as the total area of exterior wall facing in one direction on any side of a building measured from the finished ground level to the uppermost ceiling, except as follows: where a building is divided by fire separations into fire compartments, the area of exposing building face may be calculated for each fire compartment, provided such separations have not less than a 45-minute fire
SWEDISH APPROACH
Sweden has also applied basic theories of radiation to develop safe spatial separations to be applied to woodframe housing developments, which are being built in increasing numbers and to higher densities than in the past. The new Swedish regulations are intended to provide protection against conflagration by dividing building development into building groups and main building groups, separated by protective lanes and protective belts respectively. These should be wide enough to prevent pilot ignition from one side of the lane or belt to the other. The width of these lanes and belts is the spatial separation. The regulations establish a maximum size of building group and main building group based on consideration of such factors as first alarm response time, fire brigade capacity, the surface burning characteristics of the interior linings and grade slope within the development. The regulations also include diagrams which have been calculated to give the required spatial separations for a variety of construction conditions, including geometry of building face, percentage of window openings, type of exterior wall and interior lining.
Both the Canadian and Swedish approaches incorporate regulations that will permit the use of combustible construction and combustible cladding, subject to adequate spatial separations based on consideration of radiation hazard being provided between buildings. The objective in both cases is to provide protection of adjoining buildings until the fire department arrives, and the calculations must therefore assume a fire alarm response time.
The final section of this paper reviews the development of fire insurance practices and examines briefly their impact on the use of wood in construction.
HISTORY
Purcell and Thomson (24) point out that the great fire of London, which destroyed about 13 000 buildings over an area of 430 acres in 1666, emphasized the need for a fire insurance system and led directly to the establishment of the first fire insurance office in London in 1680. Early British companies subsequently extended their operations to the United States in 1735 and later to Canada, and the first purely Canadian company was organized in 1890.
Initially these companies did not fully appreciate the principle of "spread of risk" and were inclined to limit their insurance portfolios to one area only. This led to several financial failures when heavy property losses occurred. as in the great fire of New York City in 1835 and the Boston fire of 1872. Fire insurance companies in the United States and Canada are now required by law to hold specified amounts of capital in reserve, the amount being dependent on the volume of insurance underwritten by the company.
Historically, fire insurance companies tended to avoid the underwriting of wood-frame houses, and their rates on such houses have been traditionally higher than on masonry construction. This attitude is changing, and today in many areas of the United States and Canada there is little or no difference in fire insurance rates for masonry and woodframe housing. This has come about in the first instance from improved statistics on fire loss. As the supply of wood-frame housing increases in an area and the factors affecting potential loss are better understood, insurers have discovered that the effect on loss ratios of differences in construction between masonry and wood-frame housing is of much less significance than was previously assumed.
COMPARATIVE RATES
The average annual premium difference between masonry and frame dwellings on a $20000 fire insurance policy in the United States varies from $7 to $30. depending on the fire protection available. Specific rates show wider variation, ranging from no difference in some areas to slightly over $50 per year in so-called unprotected territory, which is defined as an area lacking in fire protection facilities. In Canada these differentials range from no difference to about $33 per year in unprotected territory. In western Canada, where masonry dwellings are relatively uncommon, there is usually no difference in premium rate between masonry and wood-frame dwellings or, at the most, only $3 yearly. In eastern Canada, where masonry and brick veneer construction are more common, the rate difference is more apparent but still not really significant. In Montreal, for example, the premium differential is only about $5 per year.
Insurance rates also vary regionally for each type of construction, based on loss statistics for the area. This can result in rate differentials for masonry construction being greater from one area to another than the rate differential for masonry and wood-frame construction in a single area.
The effect on- rates of using wood shingle roofs is also variable between localities and companies. This may range from no increase in premium where the roof is well maintained to between $2 and $5 per year in some areas of the United States, regardless of the total amount of the policy.
It seems evident that the rate differentials, once heavily weighted against timber construction, are being minimized as improved actuarial data on fire losses are obtained. In the main, the rate differentials in North America are not great enough to be an important competitive factor in the choice between wood-frame and masonry housing, although there are still areas where better statistical information is needed to secure a more uniform and equitable basis for the determination of premiums.
FIRE LIMITS
It is appropriate here to consider briefly the controversial concept of fire limits as a means of fire protection, since these have been instigated mainly by fire insurance interests. Fire limits are widely applied in the United States but are not used to any great extent in Europe. In concept they are a form of zoning aimed at prohibiting certain types of construction in specific areas within a city. In effect, their adoption has led to the virtual prohibition of wood-frame construction in mercantile or high value districts. The proponents of fire limits claim that they permit the application of more restrictive fire safety requirements to designated areas within a city without the need for these same requirements to be applied elsewhere. The purpose of fire zones is to prevent a conflagration arising from rapid spread of fire between buildings.
In certain modern building codes, including the National Building Code of Canada, the concept of fire limits has been rejected and the problem dealt with in other ways, mainly through the incorporation of spatial separations between buildings, which are related in turn to the percentage of unprotected openings and the type of exterior wall construction. The assumption is that, providing these fire separation requirements are enforced, a conflagration hazard will not develop and the need for additional controls through the creation of fire zones will not exist.
It would appear that this modern code approach should be encouraged and fire limits discouraged as a means of controlling fire spread, if wood-frame construction is not to be unduly restricted in its application.
There is clear evidence that the enactment of building legislation can lead to the development of building regulations that can markedly affect the application of timber in building construction. Under some building codes it can be difficult and even impossible to use wood or wood-based products to their full potential. Many of these difficulties can be avoided and others reduced if building regulations are based on full consideration of current technology, prepared by those with the necessary technical expertise, and designed to permit flexibility in application.
It is important to distinguish clearly between building legislation and planning legislation. The former should be restricted to structural safety, fire protection and health aspects of building, and should not include planning matters such as zoning, density and height limitations, except where these relate directly to safety considerations. In addition, there is much merit in segregating the building regulations which are the technical instruments for implementing the Building Act, and which must be capable of regular amendment, from those requirements which represent law and which can be expected to remain unchanged for relatively longer periods of time.
The development of uniform building regulations for application over a wide geographical area is considered advantageous because it facilitates:
the work of builders and designers who operate in more than one area;
the marketing of manufactured products on a national scale;
the development of training courses to meet the needs of the building industry;
the development of standard testing, evaluation and certification procedures on a national basis.
A useful mechanism in the promotion of uniform building regulations has been the development of "model" codes. These are prepared as advisory documents and offered for adoption to appropriate authorities. A major strength of this approach is its ability to apply a broad range of expertise to the preparation and regular updating of the code. The application of uniform regulations over a broad geographical area is achieved by drafting the regulations so that the specific requirements which vary with climate are related to the basic climatic data for each locality. Condensed versions of these model codes can meet the needs of most smaller communities, and merit consideration for the developing countries.
Regulations written in specification form, stating the kinds of materials and the manner in which they may be used, have been a prime cause of restriction on the introduction of new or nontraditional materials or methods of construction. Modern thinking is that building control should be phrased so that the designer and builder are given freedom to use any material or design technique they wish, provided the completed building affords the necessary protection to the occupants with respect to structural sufficiency. fire prevention and health. Many current codes attempt to achieve this by incorporating an escape clause which specifically empowers the authority having jurisdiction to accept new methods and materials where their suitability has been established by test or experience or through accepted engineering analysis. In practice, this clause is difficult to implement since its application generally depends on the availability of adequate performance criteria against which to assess the proposed construction, and there are practical difficulties in the development of such criteria. Nevertheless, there is a strong interest in the performance approach as one of the most suitable ways of satisfying the basic principle that no form of construction should be excluded as long as it meets the intent of the code.
A technique for applying the performance approach that offers particular advantage to developing countries is to frame the regulations in functional or performance terms and provide practical guidance on how the result can be achieved through the development of deemed-to-satisfy clauses. This allows traditional methods and materials to be used without being mandatory, and permits the assessment of new or nontraditional forms of construction against performance criteria as and where appropriate.
Some form of central or national evaluation scheme can facilitate the acceptance of new forms of construction and help to ensure uniformity and application of the regulations in various areas. The national system known as Agrément is one example and the central evaluation services provided by the model code groups in the United States are another. These systems are of most value when used in association with nationally accepted building regulations and building standards. They must be evaluated, however, in terms of their added cost and the loss of flexibility that is inherent in the traditional system of operation.
An examination of specific building code requirements indicates that restrictions on the use of wood arise chiefly from clauses designed to regulate structural stability, durability and fire safety. There are few unnecessary restrictions on the structural use of timber in the national codes of those countries which have a long tradition of timber construction. It is significant, however, that in such countries there exists an extensive background of research in timber, a large body of technical knowledge-much of which has been incorporated in codes of practice and standards, and a system of quality control of lumber grades through a national system of grade marking, all of which form a vital part of the regulatory aspects.
Correspondingly, durability requirements in codes do not need to place onerous restrictions on the use of timber, providing the characteristics and relative durabilities of the local species are documented.
The matter of fire safety, and uncertainty as to the behaviour of timber in fire situations, are by far the most important factors leading to building regulations which do discriminate against the use of timber. The problem arises primarily through concern over the combustible nature of wood, combined with an approach which places heavy emphasis on combustibility as a measure of the hazards involved and tends to ignore more recent studies relating to the performance of structural systems exposed to fire.
Design for fire safety is still far from being on the same rational basis as that of structural design; nevertheless, fire research during the last decade has done much to improve basic knowledge in this field. Such studies have permitted a more rational approach in modern codes which in turn permit much greater freedom in the use of timber and timber products than was possible under earlier regulations. Although this paper has discussed these developments chiefly with reference to Canada, similar approaches to the framing of fire regulations will be found in the national codes of other countries, including Sweden and the United Kingdom.
Regulations which rely on a scientific approach, based on functional requirements wherever possible, are required if the arbitrary restrictions imposed on timber by the older specification codes are to be avoided. An important related factor is the development and acceptance of standard test methods as a means of assessing the fire protection aspects of construction. There is an increasing measure of international agreement on such tests, assisted greatly by the work of the International Standards Organization, but much still needs to be done in certain areas. Flame spread tests, for example, vary widely between countries and because of this no comparison of the legislative requirements in the different countries is yet possible.
Interaction between building code committees and national building research studies has proved a valuable stimulant to code improvement. In general, countries with more developed timber industries, longer traditions of timber building and national building and timber research programmes, have exhibited more permissive attitudes in the regulation of timber construction than those with more limited resources or experience. The importance of such experience is reflected in the attitudes of fire insurance companies which initially tended to avoid the underwriting of wood-frame houses but more recently, on the basis of improved statistical information, have established annual premium rates which differentiate little between masonry and frame dwellings.
A fitting conclusion to this review is Bonaldi's statement in the final paragraph of his paper (20):" Developing countries can gain much from the mistakes and experience of other countries. They should start with good legislation followed by sound codes, both based on modern philosophy and prepared by experts only, in daily contact with the design and construction of buildings and with the help of sound research."
|
Building bylaw |
A legal rule or set of rules concerning building safety which derives its authority from superior legislation such as an enabling Act. |
|
Building regulations (or building code) |
Written statements, either legal or other wise used voluntarily or by force of law or other authority to control building in the field of safety. Building regulations may include codes, bylaws, standards, etc. |
|
Deemed-to-satisfy |
Refers to materials or methods of construction which may be used to meet the requirements of particular regulations but which are not in themselves mandatory. |
|
Specification |
A concise statement of requirements regarding a particular product, material or process. |
|
Standard |
The result of a particular standardization effort by a recognized authority. It generally takes the form of a document containing a set of conditions to be ful filled and may be considered as a " specification" for recurrent use. |
(1) SCOTLAND, LAWS, STATUTES, ETC. 1959 Building (Scotland) Act 1959. London, HMSO.
(2) SCOTLAND. LAWS, STATUTES, ETC. 1963 Building standards (Scotland) regulations 1963. London, HMSO.
(3) NATIONAL RESEARCH COUNCIL, CANADA. ASSOCIATE COMMITTEE ON THE NATIONAL BUILDING CODE. 1970 National Building Code of Canada 1970. 5th ed. Ottawa. NRC 11246.
(4) GARSTON, ENGLAND. BUILDING RESEARCH STATION. 1963 Model regulations for small buildings: tropical building legislation. London, HMSO.
(5) CANADIAN STANDARDS ASSOCIATION. Code of recommended practice for engineering design in timber. Ontario.
(6) BRITISH STANDARDS INSTITUTION. Code of practice for the structural use of timber. London.
(7) DOBSON, D.E. 1968 Building regulations: a review of the position in some western countries. Pretoria, National Building Research Institute. CSIR Research Report 269.
(8) CANADIAN STANDARDS ASSOCIATION. 1960 Determination of non combustibility of building materials. Ontario. B 54.1.
(9) AMERICAN SOCIETY FOR TESTING AND MATERIALS. Non-combustibility of elementary materials. Philadelphia, Pennsylvania. E 136.
(10) CANADIAN STANDARDS ASSOCIATION. 1964 Methods of fire tests of walls, partitions, floors, roofs, ceilings, columns, beams and girders. Ontario. B 54.3.
(11) CANADIAN STANDARDS ASSOCIATION. Standard methods of fire tests of door assemblies. Ontario. B 54.2.
(12) NATIONAL RESEARCH COUNCIL, CANADA. ASSOCIATE COMMITTEE ON THE NATIONAL BUILDING CODE. 1954 Fire resistance ratings. Appendix 4-1-B to the National Building Code. Ottawa.
(13) AMERICAN SOCIETY FOR TESTING AND MATERIALS. 1968 Test for surface burning characteristics of building materials. Philadelphia, Pennsylvania. E 84.
(14) BRITISH STANDARDS INSTITUTION. 1953 Fire tests on building materials and structures. London. B.S. 476, Part 1.
(15) CIBULA, E. 1970 Systems of building control. London, HMSO. Building Research Station. Current Paper 31/70.
(16) DALDY, A.F. 1969 Scope of building legislation. London, HMSO. Building Research Station. Current Paper 20/69.
(17) HONEY, C.R. 1970 International comparison of building regulations: the content and arrangement of regulating documents. London, HMSO. Building Research Station. Current Paper 37/70.
(18) LEGGET, R.F. & HUTCHEON, N.B. 1967 Performance concept in buildings. St. Joseph, Michigan, American Society for Testing and Materials. Special Technical Publication NO. 423. (NRC 9593)
(19) LEVIS, E. 1968 Statutory controls: effect on timber design in the U.K. and abroad. Paper read at the Conference of Municipal Building Surveyors held by the Incorporated Association of Architects and Surveyors, London, 1968.
BACKGROUND PAPERS
(20) BONALDI, R.J. 1971 A study of basic legislation and code approaches to the use of wood in housing in developing countries. WCH/71/4b/5.
(21) HANSEN, A.T. 1971 The National Building Code of Canada and the use of wood in housing with special reference to fire safety. WCH/71/4b/3.
(22) DOBSON, D.E. 1971 Timber housing and building regulations: the approach in developing and developed countries. WCH/71/4b/4.
(23) ODEEN, K. 1971 Combustibles in building and how they are regulated in Scandinavia (with special reference to wood and wood products). WCH/71/4b/2.
(24) PURCELL, F.X. & THOMSON, C.R. 1971 Fire insurance practices. WCH/71/4b/6.
1. The Consultation suggested that the control of building construction has three facets-tradition, law and science. Both tradition and science, as well as written regulations, play their part in building control.
2. The Consultation recognized that building codes can be important instruments in establishing standards of safety with respect to fire, health and structure; however, such codes should be prepared with full consideration of the life style, level of technology and economic position within each country, and should always be firmly based on the results of research in building science. It is essential that codes be sufficiently flexible in form and application so as not to hinder the introduction and use of materials or systems of construction that can be shown to be satisfactory.
3. The Consultation considered that the ultimate solution to the flexibility problem was through the development of building codes based on performance and it recommended that governments and other code-writing bodies be encouraged to work toward this ideal. It noted that the preparation of such codes would be greatly assisted through the pooling of knowledge and the sharing of technical expertise relating to the performance concept in the most embracing sense. However, it also noted that the practical difficulties associated with the development and use of a code based completely on performance would force most countries to place greater reliance on documents of a specification type until adequate test procedures and technical expertise had been developed.
4. The Consultation recommended that governments and other code-writing bodies when developing performance requirements should also develop detailed technical solutions to meet these requirements. These technical solutions can be in the form of standards, specifications or codes of practice which can serve as deemed-to-satisfy documents indicating the various practical methods of complying with the performance requirements.
5. The Consultation proposed that the appropriate international agencies sponsor the preparation of model codes for application in developing countries with simliar levels of social and technical development. Such codes can malice provisions for differing climatic conditions by relating the appropriate code requirements to supplementary climate data for each area. The development of a common code for Scandinavia, due to be promulgated in 1975, and the work of the United Nations Economic Commission for Africa in developing a small code for houses, were cited as examples of the type of action required.
6. The Consultation was informed that the United Nations Economic Commission for Europe (ECE) was examining the question of harmonizing building regulations and that the subject would be one of the main items at the next seminar of the ECE Committee on Housing, Building and Planning to be held in London, England, in 1973. It suggested that this ECE study might serve as a valuable basis for harmonization of building regulations on a worldwide basis. The Consultation recommended that its own report be brought to the attention of the ECE committee.
7. Noting the importance of ensuring that a building code reflects the most recent developments in research and technology, the Consultation recommended that all code-writing bodies provide for revision of their published codes on a regular basis. Revision should be at least every five years and there should be provision for issuing revisions at more frequent intervals where these are justified by technical developments. It was important that revisions be well publicized in advance of being promulgated to facilitate their proper application. To retain flexibility in the adoption of model codes by individual countries, a mechanism for revision must be available to them; wherever possible such revisions should be coordinated between users of the model code.
8. The Consultation recognized the importance of participation of all segments of the building industry in the preparation and revision of codes.
9. The need for training of personnel in all phases of code administration and application was emphasized, and the Consultation urged international agencies, in cooperation with national governments, to explore ways and means for furthering the training of persons in these relevant code aspects.
10. Recognizing that building codes are traditionally established to protect the safety of the public in regard to structure, fire and health, the Consultation agreed that such codes should provide the miminum construction requirements consistent with this purpose. It emphasized that the performance level must be established with due consideration to the social, technical and economic standards of each country or region in which the code is to be applied.
11. The Consultation strongly recommended that government bodies and private agencies, such as insurance companies, which are concerned with fire, arrange for the collection and reporting of comparative statistical information on property and life losses in building fires, and their causes. Such statistics should provide information on cause and frequency of fire in buildings of various types of construction and in different geographic areas. It recognized that these statistics were needed to establish the relative hazards of different forms of construction.
12. Noting that in countries with long traditions of wood construction, and with detailed records of fire losses and good fire-fighting methods, the insurance premiums for wood buildings indicate only minor differences from those for other types of construction, the Consultation recommended that statistical information on property losses in developing countries be applied to the determination of insurance rates for wood construction and in this way provide the basis by which to reduce wide differences in such rates where these occur.
13. The Consultation recognized the merits of a uniform system among those countries using a common model code for obtaining interpretations and evaluations of construction materials, and methods in relation to their use, under the provisions of a building code. The Consultation also noted that the International Council for Building Research Studies and Documentation (CIB), the American Society for Testing and Materials (ASTM) and the Reunion internationale des laboratoires d'essais et des recherches sur les matériaux et les constructions (RILEM) were holding a joint conference in the United States, in May 1972, on evaluation techniques in relation to performance concept, and recommended that the relevant sections of its own report be referred to the organizers of that meeting.
