Reference Standards

Appendix 7:

Reference Standards

The following are building standards, relevant to timber frame construction and are referenced in the TGDs: Loading: BS 6399: Loading for Buildings Part 1: 1984, Code of Practice for Dead and Imposed Loads AMD 4949 (Superseded by: Part 1 1996, Code of Practice for Dead and Imposed Loads) BS 6399: Part 2: 1988, Code of practice for imposed roof loads (Superseded by BS 6399: Part 2: 1997, Code of practice for imposed roof loads AMD 13392) BS 6399: Design Loading for Buildings Part 3: 1988, Code of Practice for Imposed Roof Loads AMD 6033 CP3: Chapter V: Part 2: 1972, Wind Loads (Superseded by BS 6399: Part 2: Code of practice for wind loads) Foundations: BS 8004: 1986,Code of practice for foundations Structural work on timber: IS 193: 1986, Timber trussed rafters for roofs SR 11: 1988, Structural timber for domestic construction (Superseded by IS 444: 1998, Use of structural timber in buildings) BS 5268: Structural Use of Timber Part 2: 1991, Code of Practice for Permissible Stress Design, Materials and Workmanship AMD 8597 (Superseded by Part 2: 2002, Code of Practice for Permissible Stress Design, Materials and Workmanship) BS 5268: Structural Use of Timber Part 6: Code of Practice for Timber Frame Walls, Section 6.1: 1988, Dwellings not exceeding three storeys AMD 6743 (Superseded by Part 6: Code of Practice for Timber Frame Walls, Section 6.1: 1996, Dwellings not exceeding four storeys AMD 9256 IS 96: 1976 - Moisture content of timber for building This specification relates to the limiting values of the moisture content of hardwood and softwood timber for housing and general building purposes. IS 127: 1990 - Specification for stress grading of softwood timber This standard specifies two methods of grading softwood for structural use, namely, visual stress grading and mechanical stress grading.

Timber must be marked with the appropriate stamp

designating the strength class, the grading standard (IS 127), a means of identifying the company, the certification body (NSAI) and the design standard (IS 444). Appendices

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IS 193: 1986 - Timber trussed rafters for roofs This specification covers the requirement for materials, design, fabrication and erection of fink and non-fink timber trusses for roofs. The truss is assumed to be fabricated from timber of a specified species and grade using metal plate connectors as the jointing method. IS 444: 1998 - The structural use of timber in buildings This Irish standard covers the use of structural softwood timber in buildings. For the purposes of the design of timber members, values of permissible stresses and moduli of elasticity for different strength classes are specified for the various domestic and imported species of timber. Design information is also given on the requirements for floor and ceiling joists, rafters, studding and purlins, and for these members, permissible span tables are given which specify the maximum spans for specified loadings, cross-sections and strength classes.

The moisture content

requirements of timber are also covered. IS 444 assumes that the environmental conditions are such that the average moisture content of softwood timber will not exceed 20% and that at the time of construction, the moisture content of the timber will have no greater value than 24%. IS EN 335: 1993 - Durability of wood and wood-based products This code of practice defines five hazard classes which represent the different service situations to which wood and wood-based products can be exposed, and indicates the biological agencies relevant to each situation. IS EN 336: 1995 - Structural timber - coniferous and poplar - sizes, permissible deviations This standards specifies permitted deviations (due to variability in sawing and machining) from target sawn and prepared thicknesses, and widths and lengths for structural timber of coniferous species.

It also specifies the moisture content to be used as a reference point for the

measurement of sizes, and gives average values for changes in size due to changes in moisture content. It is applicable to sawn and prepared square-edged timber with parallel edges having sawn thicknesses or widths in the range 24 mm to 300 mm. IS EN 338 :1995 - Structural timber - Strength Classes This standard establishes a system of strength classes for general use in structural codes. It gives characteristic strength and stiffness properties and density values for each class and the rules for the allocation of timber populations (i.e. combinations of species, source and grade) to the classes. This standard applies to all softwood and hardwood timber for structural use. IS EN 385: 1995 - Finger jointed structural timber - Performance requirements and minimum production requirements Appendices

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This standard specifies requirements for bonded finger joints and minimum requirements for the manufacture of cut, interlocking, bonded finger joints in structural timber members. Requirements are given for timber, adhesive, moisture content, cutting, bending and preservative treatments and flame-retardant treatments. This standard is only applicable to finger joints between timber members of the same species type. Although most finger joints are produced in coniferous species this standard also applies to broad-leaved species where information is available to enable them to be satisfactorily bonded. IS EN 518: 1995 - Structural timber - Grading - Requirements for visual strength grading standards This standard identifies the characteristics for which, as a minimum, limits shall be given in visual grading rules. This standard applies to both softwood rules and hardwood rules and covers visual sawn timber of all species likely to be used for load-bearing structural purposes. IS EN 519: 1995 - Structural timber - Grading - Requirements for machine strength graded timber and grading machines This standard specifies the requirements for assessing and operating machine strength grading systems, to strength grade structural timber, and laminates for glue laminated structures.

In

addition, guidance is given for the degree of quality control necessary to ensure the reliability of timber graded by strength grading machines. These are given for both ‘machine controlled’ and ‘output controlled systems for grading timber. IS EN 1912: 1998 - Structural timber - Strength classes - Assignment of visual grades and species This European Standard lists visual strength grades, species and source of timber, and specifies the strength classes from ISEN 338, to which they are assigned. BS 5268: Structural use of timber BS 5268: Part 2: 2002, Code of practice for permissible stress design, materials and workmanship Provides guidance on the structural use of timber, glued laminated timber, plywood, and other recommendations on quality, grade panel products in load-bearing members. It includes stresses and modification factors applicable to these materials when used as simple members, or as parts of built-up components, or as parts of structure incorporating other materials. It also gives recommendations for the design of nailed, screwed, bolted, dowelled, connected and glued joints. Appendices

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In addition, it provides recommendations for a method of test to assess the adequacy of structural assembles, and it includes general advice on workmanship, various treatments that can be applied, inspection and maintenance. It does not, and it is not intended to, deal comprehensively with all aspects of timber construction. In particular, it does not cover well-tried and traditional methods of timber construction, which have been employed successfully over a long period. BS 5268: Part 3: 1998, Core of practice for trussed rafter roofs This part of BS 5268 provides guidance on the design, fabrication and use of trussed rafters for roofs. Guidance is provided on structural analysis methods, engineering design criteria and design by testing. Performance requirements for floor bracing are given together with standard bracing arrangements for domestic scale roofs. Production requirements for truss manufacture, along with guidance on their handling, storage and erection are also given. BS 5268: Part 4: Fire resistance of timber structures, Section 4.1: 1978, Recommendations for calculating fire resistance of timber member This section of BS 5268 gives recommendations for assessing the fire resistance of flexural tension and compression members of solid or glued laminated timber and their joints. BS 5268: Section 4.2: 1990, Recommendations for calculating fire resistance of timber stud walls and joisted floor constructions This section of Part 4 of BS 5268 gives recommendations for calculating the fire resistance of timber frame walls and partitions and joisted floors as an alternative to testing. The recommendations are applicable to single and double-leaf walls and partitions; and to floors in which the joists are fully or partly concealed. This Section of BS 5268: Part 4 is limited to constructions having a fire resistance of 1 hour or less. BS 5268: Part 5: 1989, Code of practice for the preservative treatment of structural timber This part of BS 5268 gives recommendations for preservative treatment of timbers to be used for structural purposes in the United Kingdom to protect them from degradation by wood-destroying organisms. It does not cover the remedial treatment of existing timber in old buildings, nor does it deal with the protection of timber against fire, or with preserving the appearance of timber against weathering or staining. BS 5268: Part 6: Code of practice for timber frame walls Section 6.1: 1990, Dwellings not exceeding four storeys This section of BS 5268 gives recommendations for the design, testing, fabrication and erection

Appendices

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of timber frame walls for dwellings not exceeding four storeys and consisting of timber frame walls, with studs not exceeding 610 mm centres and one or both faces of the studs being partly or wholly connected to sheathing, lining, or other forms of bracing. BS 5268: Section 6.2: 2001, Buildings other than dwellings not exceeding four storeys This section of BS 5268 gives recommendations for the design, testing, fabrication and erection of timber frame walls for buildings other than dwellings not exceeding four storeys in height and where the following conditions apply: The maximum overall height of any building is 15 m. The maximum panel height in a single storey building is 6.2 m. The maximum panel height in buildings of more than one storey is 4.8 m. BS 5268: Part 7: Recommendations for the calculation basis for span tables Part 7.1: 1989 Domestic floor joists Part 7.2: 1989 Joists for flat roofs Part 7.3: 1989 Ceiling joists Part 7.4: 1989 Ceiling binders Part 7.5: 1990 Domestic rafters Part 7.6: 1990 Purlins supporting rafters Part 7.7: 1990 Purlins supporting sheeting or decking Eurocode 5 – Design of timber structures ENV 1995-1-1: 1993, General rules and rules for building Eurocode 5 uses limit state principles as the basis of design. A range of partial factors and characteristic values for loads and material properties are used in contrast with the permissible stress values and working loads adopted by BS 5268 and IS 444. Limit states are states beyond which the structure no longer satisfies the design performance requirements. These requirements are that: No relevant limit state is exceeded. All relevant design situations and factored load cases shall be considered. Possible deviations from assumed load directions and positions shall be considered. Ultimate limit states are those associated with collapse, or with other forms of structural failure that may endanger the safety of people: Appendices

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Loss of equilibrium of the structure or any part of it. Failure by excessive deformation, rupture or loss of stability. Serviceability limit states correspond to states beyond which specified service criteria are no longer met: Deformations or deflections that affect the appearance or use of a structure, or cause damage to finishes or non-structural elements. Vibration causing discomfort, damage to building or contents, or limiting functional effectiveness. ETAG 007 Guideline for European Technical Approval of Timber Frame Building Kits Compliance with ETAG 007 will ultimately enable the manufacturer to ‘CE’ mark their product which empowers the manufacturer to legally market their product throughout the EC. ETAG 007 covers industrially prepared timber frame kits, marketed as a building, which are made of predesigned and prefabricated components. This ETAG covers manufacturers of the complete house kit, i.e. manufacturers who operate a ‘one stop shop’ service. It should be noted that over 90% of timber frame production in the UK and Ireland is in the form of open panels and, as such, is not covered by this ETAG. However, a house kit manufacturer is required to comply with the procedures of the member state, e.g. the design process and approval of detailed plans, etc. Furthermore, the house kit manufacturer is required to conform with the Building Regulations of the member state. The ETAG does not, in any way, supersede or negate the Building Regulations or construction requirements of the member state. This guideline sets out the minimum performance requirements for the following: Timber frame kits used in building construction The verification methods used to examine the performance of the kits The methods used to evaluate the performance for their intended use The presumed conditions for the design and erection of the kits

Appendices

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These minimum requirements comprise the entire external envelope including all necessary thermal insulation and the internal linings in so far as they are necessary for the satisfaction of the essential requirements applied to the building. Components such as windows, roofing materials, internal linings and cladding materials shall always be assessed and specified for the fitness for use with the timber frame kit. The connections and detailing of the interface between such components and the kit shall always form part of the kit description. However, it is not a requirement for the manufacturer to supply these components as part of the kit. Although some components may be prepared in different factories, only the final kit may be CE marked by the manufacturer, should they be deemed by an appropriate approval body to have met the requirements of ETAG 007. Verification of the performance of timber frame building kits requires an assessment of many construction details with respect to air tightness, thermal efficiency, fire resistance and acoustic performance. Furthermore, durability and strength must also be assessed. While this appears to be an exhaustive approach, relevant standardised verification methods may not be available or judged to be necessary, since the performance of many construction details has been proven acceptable by long term experience or has been deemed acceptable following appraisal by an appropriate approval body of the member state. According to ETAG 007, the minimum content of the timber frame kit to be assessed includes: All structural elements necessary for the stability of the building including walls, floors, roof structures, their connections, and the connections of the building to the substructure. All components of the external envelope, including all necessary thermal insulation, internal linings, fire protection, vapour control provisions and external waterproofing. All components of the internal walls including acoustic insulation, internal linings and fire protection. Preparatory measures for the installation of plumbing, heating, cooling, ventilation and electrical services. The ETAG also insists that components such as windows, external doors, brick cladding, internal linings and roofing, which are essential for the performance of the external envelope, shall always be specified and assessed as a condition for the fitness of use of the kit even though they may not be delivered by the kit supplier. The connections and detailing of the interface between such components and the kit should always be part of the timber frame kit description.

Appendices

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Timber frame kits are assumed to have a minimum working life of 50 years for load-bearing structure and for non-accessible components and materials, and a minimum 25 years for repairable or replaceable components and materials like claddings, roofing materials, exterior trims and integrated components like windows and doors, provided that the kit is subject to appropriate use and maintenance. With regard to water tightness ETAG 007 recommends that the external envelope be designed according to the ‘two-stage principle’, that is, a ventilated and drained cavity between the inner structural and outer weathering leaf. The assessment of the resistance against driving rain into the external envelope is to be based on present design and engineering knowledge.

Where this

knowledge does not apply it is a requirement to test the external envelope performance according to a series of laboratory tests. ETAG 007 also provides guidance regarding assessment of a complete timber frame house kit with respect to: Safety in case of fire Hygiene, health and environment Safety in use Protection against noise Energy economy and heat retention Aspects of durability, serviceability and identification

Appendices

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