BS-8297-1995.pdf

BRITISH STANDARD BS 8297:1995 Code of practice for Design and installation of non-loadbearing precast concrete cladding Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 05:40:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 8297:1995 This British Standard, having been prepared under the direction of the Technical Committee B/209, General Building Codes, was published under the authority of the Standards Board and comes into effect on 15 January 1995 © BSI 02-1999 First published as CP 297, July 1972 First published as BS 8297 January 1995 The following BSI references relate to the work on this standard: Committee reference B/209/22 Draft for comment 92/14042 DC ISBN 0 580 23146 1 Committees responsible for this British Standard The preparation of this British Standard was entrusted by Technical Committee B/209, General Building Codes, to Subcommittee B/209/22, Concrete Cladding, upon which the following bodies were represented: Building Employers Confederation Chartered Institute of Building Chartered Institution of Building Services Engineers Department of the Environment (Construction Directorate) Local Authority Organizations National Council of Building Material Producers National House-building Council Royal Institute of British Architects Royal Institution of Chartered Surveyors The following bodies were also represented in the drafting of the standard, through subcommittees and panels: Association of Consulting Engineers British Adhesives and Sealants Association British Non-ferrous Metals Federation British Precast Concrete Federation Ltd. Department of the Environment (Building Research Establishment) District Surveyors Association Federation of Civil Engineering Contractors Institute of Clerks of Works of Great Britain Inc. Institution of Civil Engineers Institution of Structural Engineers Amendments issued since publication Amd. No.DateComments Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 05:40:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 8297:1995 © BSI 02-1999i Contents Page Committees responsible Inside front cover Foreword iii Section 1. General 1.1Scope 1 1.2References1 1.3Definitions1 1.4Exchange of information and time schedules2 Section 2. Materials and components 2.1 Materials for precast concrete4 2.2 Fixings4 2.3 Jointing and pointing materials5 2.4 Flashings, weatherings and cavity trays6 2.5 Coating agents6 Section 3. Design considerations 3.1 General7 3.2 Cladding units7 3.3 Cavities25 3.4 Cavity barriers to resist spread of fire26 3.5 Weathering and water run-off26 3.6 Flashings and weatherings26 3.7 Accommodation of dimensional changes26 3.8 Atmospheric pollution29 3.9 Frost action30 3.10 Staining30 3.11 Compatibility30 3.12 Signs30 Section 4. Workmanship 4.1 Supervision31 4.2 Production31 4.3 Workmanship on site32 4.4 Erection32 4.5 Protection34 4.6 Site repairs34 4.7 Cleaning on completion of work34 Section 5. Inspection and testing 5.1General36 5.2Testing authority36 5.3Test specimens36 5.4Required information36 5.5Reporting36 5.6Test sequence37 5.7Design test pressures37 5.8Air permeability tests37 5.9Water penetration tests37 5.10 Wind resistance tests37 5.11 Optional loading procedures38 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 05:40:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 8297:1995 ii © BSI 02-1999 Page Section 6. Maintenance 6.1General 39 6.2Granite39 6.3Marble39 6.4Slate and quartzite39 6.5Limestone and sandstone39 6.6Clay bricks39 6.7Concrete finishes and cast stone39 Annex A (informative) Subjects covered in BS 8200 Code of practice for the design of non-loadbearing external vertical enclosures of buildings41 Annex B (normative) Water penetration test by dynamic pressure41 Annex C (normative) Thermal cycling regime42 Figure 1 Assumptions for design of units and corbels/brackets10 Figure 2 Corbel and nib details11 Figure 3 Jointing profiles with sealants15 Figure 4 Open drained joint with plain baffle16 Figure 5 Structural support angle18 Figure 6 Restraint fixings19 Figure 7 Restraint fixing at bottom of panel19 Figure 8 Restraint fixing at head of panel20 Figure 9 Projection showing loadbearing and restraint fixings20 Figure 10 Typical details of fixing pins for granite faced concrete units25 Table 1 Flashings, weatherings and cavity trays 6 Table 2 Thickness of cover for mixes and strengths of concrete9 Table 3 Minimum thickness of fire-resisting wall units9 Table 4 Specified minimum mechanical properties in BS 970-1 and BS 1449-221 Table 5 Mechanical properties of austenitic stainless steel fasteners to BS 610521 Table 6 Working stresses for stainless steel bolts in clearance holes21 Table 7 Origins of movement in structures27 Table 8 Coefficients of thermal expansion of buildings materials28 Table 9 Extreme temperatures of UK structures28 Table 10 Rate of shrinkage of concrete (as a percentage of its potential)29 Table 11 Permissible deviations31 Table 12 Test pressures37 List of references44 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 05:40:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 8297:1995 © BSI 02-1999iii Foreword This British Standard has been prepared under the direction of Technical Committee B/209, General Building Codes. It supersedes CP 297:1972 which is withdrawn. With framed structures, where the loads are carried by the frame and not by the external walling, the materials or combinations of materials used to cover the structural framework are referred to as the cladding. Cladding, in the form described in this standard, requires care to ensure secure fixing and to prevent or control the ingress of water. Adequate precautions have also to be taken to provide for permanent and temporary movements of the structure due to shrinkage and elastic deformation under load. Movement due to temperature and other factors has also to be taken into account. This standard describes the provisions necessary for the cladding to perform its function satisfactorily. It gives the minimum standards needed and the materials and methods most frequently used. Assessed capability. Users of this British Standard are advised to consider the desirability of assessment and registration of a suppliers quality systems against the appropriate Part of BS 5750 by a third party certification body. Enquiries as to the availability of third party certification schemes will be forwarded by BSI to the Association of Certification Bodies. If a third party certification scheme does not already exist, users should consider approaching an appropriate body from the list of Association members. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 46, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 05:40:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 05:40:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 8297:1995 © BSI 02-19991 Section 1. General 1.1 Scope This British Standard gives recommendations for the design and installation of precast concrete cladding in the form of: a) units supported by and fixed to a structural frame or wall; b) units used as permanent formwork in part or in whole. The cladding can be self-finished or may carry integral factory cast-in finishes, such as natural stone, bricks, tiles and mosaics. The standard includes precast cladding using specially formulated and designed mixes to provide special finishes in terms of colour and texture. The finishes include reconstructed stone. Loadbearing cladding and glass reinforced cement units are not covered by this standard. 1.2 References 1.2.1 Normative references This British Standard incorporates, by dated or undated reference, provisions from other publications. These normative references are made at the appropriate places in the text and the cited publications are listed on page 44. For dated references, only the edition cited applies; any subsequent amendments to or revisions of the cited publication apply to this British Standard only when incorporated in the reference by amendment or revision. For undated references, the latest edition of the cited publication applies, together with any amendments. 1.2.2 Informative references This British Standard refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on the page 46, but reference should be made to the latest editions. 1.3 Definitions For the purposes of this British Standard the definitions given in BS 6100 apply, except as otherwise defined in this clause. Other terms which are particularly relevant are also defined. 1.3.1 back-up material material inserted in a joint which limits the depth of the sealant applied and which determines the back profile of the sealant 1.3.2 baffle1) flexible preformed section designed to be fitted in grooves between the adjacent units to minimize direct entry of rain into an open joint 1.3.3 bimetallic corrosion corrosion caused by contact between dissimilar metals in the presence of an electrolyte, such as water 1.3.4 cavity barrier construction provided to close a concealed space against penetration of smoke or flame, or provided to restrict the movement of smoke or flame within such a space 1.3.5 cladding1) form of building covering that supports only its own weight and environmental forces that may act upon it 1.3.6 composite unit cladding unit having a facing of materials other than concrete 1.3.7 Fixings 1.3.7.1 loadbearing fixing fixing designed to support the dead weight of one or more cladding units and to transfer this load directly to the structure 1.3.7.2 location fixing1) temporary fixing whose sole purpose is to assist in the alignment of the cladding units 1.3.7.3 restraint fixing 1) fixing designed to tie cladding units to their backing or to one another 1.3.8 Joints 1.3.8.1 compression joint1) joint designed specifically to accommodate partial closure resulting from vertical shortening of the structure relative to the cladding 1) Definition differs from that given in BS 6100. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 05:40:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 8297:1995 2 © BSI 02-1999 1.3.8.2 filled joint joint that makes use of a jointing product to fill a gap between the adjacent components 1.3.8.3 movement joint2) joint that permits movement between adjacent parts 1.3.8.4 open joint2) completed joint taking the form of an intentional open gap between adjacent units or between a unit and the structure NOTEA baffle strip may be located in vertical open joints. 1.3.9 sealant2) material which, applied in an unformed state to a joint, seals it by adhering to appropriate surfaces within the joint 1.3.10 gasket2) flexible, generally elastic, preformed material that constitutes a seal when compressed, and that resists the passage of water and air 1.4 Exchange of information and time schedules 1.4.1 General Before tenders are invited a cladding specialist should be consulted to discuss practical time scales, availability and suitability of materials, etc. This is especially important for contracts with large quantities of special aggregates or finishes. The information needed in order to schedule the work satisfactorily, obtain an accurate price, minimize supply and production difficulties, and ensure safe and practical site fixing, is given in 1.4.2, 1.4.3 and 1.4.4. 1.4.2 Initial feasibility planning The information needed at the feasibility planning stage includes: a) total areas to be clad and their locations on the buildings; b) aesthetic and/or visual effect required, in terms of colour; jointing pattern, surface finish and durability; c) limitations on the use of the materials; d) functions of the cladding, and the type of structure to which it is to be fixed; e) variations in colour, tone and markings that can occur in the selected materials; f) approximate time between placing the order and commencing on site; g) approximate duration of the cladding work on site, taking account of the work of other trades. 1.4.3 At tender stage 1.4.3.1 Design and performance specification Cladding specialists invited to tender should be provided with the following information: a) conditions regarding the building site and site access, and any particular restrictions on the site of units or of deliveries, the time of deliveries or on storage, handling, or distributing facilities, including maximum crane capacities at different radii; b) programme and/or bar chart defining sequence and duration of site fixing, or an invitation to present recommendations; c) sufficiently explicit drawings to show the basic construction requirements, including the relationship between the structural frame and the frame of the cladding units, unit thicknesses, jointing (including movement joints) and any special cladding or labours; d) building tolerance(s) allowed in the structure; e) type(s) of materials and finishes, and any demands on matching or selection, or limits on variations in appearance; f) type of pointing, where applicable; g) type of sealant; h) method of fixing to be used, or an invitation to present a suitable method; i) any requirements for the routine, or special, testing of components, before or after erection, or for sample areas or mock-up panels and whether tested units should be retained or placed on the building; j) criteria for the acceptance or rejection of individual units and fixings. 1.4.3.2 Facilities and materials required on site To prevent misunderstanding, particularly when tenders are being called, it should be made clear whether or not the following will be provided and by whom: a) tower, or mobile crane, for offloading, distributing and raising cladding to fixing positions at each level, and elevation; 2) Definition differs from that given in BS 6100. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 05:40:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 8297:1995 © BSI 02-19993 b) hard and level access road on to site and to hoisting positions all suitable for passage and working of delivery vehicles and mobile cranes; c) safe storage areas, with firm level access, for us