SOUTH AFRICAN NATIONAL STANDARD Construction works Part ... · ISBN 978-0-626-22646-6 SANS 2001-CT2:2009 Edition 1.1 SOUTH AFRICAN NATIONAL STANDARD Construction works Part CT2: Structural

ISBN 978-0-626-22646-6 SANS 2001-CT2:2009Edition 1.1

SOUTH AFRICAN NATIONAL STANDARD

Construction works

Part CT2: Structural timberwork (roofing)

SANS 2001-CT2:2009 Edition 1.1 Table of changes Change No. Date Scope

Amdt 1 2009 Amended to update referenced standards. Acknowledgement The SABS Standards Division wishes to acknowledge the input of the Joint Structural Division of the South African Institution of Civil Engineering and the Institution of Structural Engineers in the development of this part of SANS 2001. Foreword This South African standard was approved by National Committee SABS SC 59D, Construction standards – Timber structures, in accordance with procedures of the SABS Standards Division, in compliance with annex 3 of the WTO/TBT agreement. This part of SANS 2001 was published in April 2009. This document supersedes SANS 2001-CT2:2007 (edition 1). A vertical line in the margin shows where the text has been technically modified by amendment No.1. SANS 2001 consists of a number of parts in various stages of preparation, under the general title Construction works. Annexes A and B form an integral part of this part of SANS 2001. Annex C is for information only. Introduction The different parts of SANS 2001 each address a specific component of construction works. The prime purpose in the production of these standards is to create a set of standards that are generally applicable to construction works, and which can be readily modified to make them applicable to particular works. The SANS 2001 family of standards provides technical descriptions of the standard of materials and workmanship that will be used in the works that are executed or in the performance of the works when completed (or both). These standards do not make reference to the actions of those responsible for executing the works or the parties to a contract, i.e. to the constraints relating to the manner in which contract work is to be performed. Neither do they deal with the commercial arrangements of such contracts. These standards are suitable for use in any “in-house” construction work or in all types of engineering and construction works contracts, for example, design by employer, design and build, develop and construct, construction management or management contracts. Standard requirements pertaining to the manner in which works are constructed can be found in the SANS 1921 family of standards.

SANS 2001-CT2:2009 Edition 1.1

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Construction works Part CT2: Structural timberwork (roofing) 1 Scope This part of SANS 2001 covers the construction of timber roof assemblies in buildings. It includes a) the manufacture of bolted trusses that are designed in accordance with the requirements of

SANS 10400, b) the erection of prefabricated timber trusses, c) the erection of rafters and purlin rafters, d) the fixing of purlins and battens, and e) the fixing of brandering to roofing members to support ceilings that comprise gypsum

plasterboard, fibre-cement board or similar boards. NOTE 1 Annex A provides guidance to those responsible for compiling procurement documents which make reference to this part of SANS 2001. NOTE 2 This part of SANS 2001 enables timber roof assemblies designed in accordance with the requirements of SANS 10400 to be constructed in accordance with the requirements of the National Building Regulations. Appropriate modifications might be necessary to make this part of SANS 2001 applicable to the installation of timber roof assemblies designed in accordance with the structural design requirements of SANS 10400 and the guidance given in SANS 10243. 2 Normative references The following referenced documents are indispensable for the application of this document. All normative documents are subject to revision and, since any reference to a normative document is deemed to be a reference to the latest edition of that document, parties to agreements based on this document are encouraged to take steps to ensure the use of the most recent editions of the normative documents indicated below. Information on currently valid national and international standards can be obtained from the SABS Standards Division. SANS 457-2, Wooden poles, droppers, guardrail posts and spacer blocks – Part 2: Softwood species.


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SANS 457-3 (SABS 457-3), Wooden poles, droppers, guardrail posts and spacer blocks – Part 3: Hardwood species. SANS 820, Mild steel nails. SANS 1288 (SABS 1288), Preservative-treated timber. SANS 1348, Polyvinyl acetate dispersion adhesives for wood. SANS 1349, Phenolic, aminoplastic and one-part polyurethane resin adhesives for the laminating and finger-jointing of timber, and for furniture and joinery. SANS 1460, Laminated timber (glulam). SANS 1700-7-1/ISO 4014, Fasteners – Part 7: External drive hexagon bolts and screws – Section 1: Hexagon head bolts – Product grades A and B. SANS 1700-7-2/ISO 4015, Fasteners – Part 7: External drive hexagon bolts and screws – Section 2: Hexagon head bolts – Product grade B – Reduced shank (shank diameter equal to pitch diameter). SANS 1700-7-3/ISO 4016, Fasteners – Part 7: External drive hexagon bolts and screws – Section 3: Hexagon head bolts – Product grade C. SANS 1700-14-1/ISO 4032, Fasteners – Part 14: Hexagon nuts – Section 1: Hexagon nuts, style 1 – Product grades A and B. SANS 1700-14-2/ISO 4033, Fasteners – Part 14: Hexagon nuts – Section 2: Hexagon nuts, style 2 – Product grades A and B. SANS 1700-14-3/ISO 4034, Fasteners – Part 14: Hexagon nuts – Section 3: Hexagon nuts – Product grade C. SANS 1700-14-4/ISO 4035, Fasteners – Part 14: Hexagon nuts – Section 4: Hexagon thin nuts (chamfered) – Product grades A and B. SANS 1707-2, Sawn eucalyptus timber – Part 2: Brandering and battens. Amdt 1 SANS 1783-1, Sawn softwood timber – Part 1: General requirements. SANS 1783-2, Sawn softwood timber – Part 2: Stress-graded structural timber and timber for frame wall construction. SANS 1783-4, Sawn softwood timber – Part 4: Brandering and battens. SANS 10005, The preservative treatment of timber. SANS 10096, The manufacture of finger-jointed structural timber. SANS 10243, The manufacture and erection of timber trusses. SANS 10400 (SABS 0400), The application of the National Building Regulations. SANS 10403, Formatting and compilation of construction procurement documents.


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3 Definitions For the purposes of this document, the definitions given in SANS 10403 and the following apply. 3.1 accredited certification body certification body that has been accredited by a government-endorsed accreditation body 3.2 accredited testing laboratory laboratory that has been accredited by the South African National Accreditation System 3.3 batten small section timber member, fixed parallel to the line of the eaves, at right angles to the rafters, and onto which tiles or slates are fixed 3.4 bearing structural support, usually a wall, positioned under the top chord or bottom chord or between the end points of a roof truss, beam or rafter 3.5 bottom chord tie beam horizontal or inclined member that establishes the lower edge of a truss 3.6 brandering small section timber member which is usually fixed to the underside of a truss chord to support a fixed ceiling 3.7 chord main member that forms the outline of a truss 3.8 connector device that is capable of transmitting loads from one member to another 3.9 moisture content mass of water in a sample of timber, expressed as grams of moisture per kilogram of oven-dried mass of the sample 3.10 nail plate steel plate punched to form a nail pattern integral with the plate, and which is used as a structural connector 3.11 permissible deviation pd specified limit(s) of deviation within which a dimension or position lies


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3.12 purlin horizontal member attached to, and placed perpendicular to, the rafter in order to support roof sheeting materials 3.13 rafter top chord horizontal or inclined member that establishes the upper edge of a truss 3.14 roof assembly building cover and its supporting structure, including any ceiling attached to such structure 3.15 softwood timber timber derived from trees of the genus Pinus grown in South Africa and which has been appropriately graded with respect to its intended use 3.16 specification data data, provisions and variations that make this part of SANS 2001 applicable to a particular contract or works (see annex A) 3.17 suitable capable of fulfilling or having fulfilled the intended function, or fit for its intended purpose 3.18 truss triangulated combination of members and joints which, when fitted together, form a rigid structural component capable of withstanding loads 3.19 wall plate timber strip, laid on top of walls to level the underside of beams and trusses 3.20 web member that joins the top chords and bottom chords to form triangular patterns 4 Requirements 4.1 Materials 4.1.1 Prefabricated roof trusses 4.1.1.1 Prefabricated trusses shall be designed and manufactured in accordance with the relevant requirements of SANS 10400 and SANS 10243. 4.1.1.2 Trusses shall be transported singly or banded together in bundles. When banding is used, care shall be taken to avoid damage by badly positioned or excessively tight banding. Undue sagging or flexing of single units or bundles shall be avoided and particular care shall be taken, when using mechanical handling equipment, to avoid damage by impact or rough handling.


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4.1.2 Softwood roofing timber 4.1.2.1 Softwood roofing timber shall comply with the requirements of either SANS 1460 or SANS 1783-2, and shall be of the grade and type shown in the construction drawings or specified in the specification data (see annex A). 4.1.2.2 All timber shall be ordered in the dimensions in which it will be used and shall not be sawn into smaller cross-sectional sizes. NOTE Sawing timber lengthways into smaller sizes contravenes the grading rules and invalidates the grading. 4.1.2.3 Finger-jointing of timber shall be in accordance with SANS 10096 and shall be marked accordingly. The adhesive used shall be a resorcinol type or a phenol-resorcinol type or another composition that complies with SANS 1348 or SANS 1349, as appropriate. NOTE Short lengths of timber may be converted into longer lengths in this way. 4.1.2.4 The moisture content of the timber shall not exceed 17 %. NOTE Timber is normally kiln-dried to approximately 12 % moisture content. However, timber which has been treated against biological attack using a water-borne preservative might have a moisture content well in excess of 17 % until sufficient time has elapsed to allow the timber to dry out naturally (10 d to 14 d). Excessive moisture content can be ascertained by using a moisture meter (properly calibrated) or, in extreme cases, the timber will feel damp to the touch. The accuracy of moisture meters can be affected in cases where the timber has been treated. 4.1.2.5 Unless otherwise specified in the specification data, softwood timber within the magisterial districts identified in annex B shall be treated against the effects of rot, fungus and insect attack in accordance with the requirements of SANS 10005 and SANS 1288. The cut areas of treated timber shall be thoroughly brushed with two coats of a preservative that belongs to the same class as that used in the original impregnation. During transport and installation, impregnated timber shall be protected and so handled that the impregnated shell is not broken through, and the timber is not damaged in any way that might reduce the effectiveness of the preservative. NOTE SANS 10400 requires that softwood within the municipal boundaries identified in annex B be treated. 4.1.3 Roofing poles 4.1.3.1 Roofing poles shall comply with the requirements of either SANS 457-2 (softwood) or SANS 457-3 (hardwood) and shall be of the diameter shown in the construction drawings or specified in the specification data. 4.1.3.2 All roofing poles shall be treated in accordance with the requirements of SANS 10005. 4.1.4 Battens and brandering Battens and brandering shall comply with the requirements of either SANS 1783-4 or SANS 1707-2. Amdt 1


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4.1.5 Connectors 4.1.5.1 Nails 4.1.5.1.1 Nails shall comply with the requirements of SANS 820 and shall have the dimensions given in tables 1 and 2, as appropriate. 4.1.5.1.2 In areas within 1 km from the coastline or shoreline of large expanses of salt water and within 3 km of industries that discharge atmospheric pollutants which are corrosive (for example, Mpumalanga escarpment), nails shall be corrosion treated by means of hot-dip galvanizing or sherardizing.

Table 1 — Ordinary wire nails

Dimensions in millimetres

1 2 3

Length D H 63 75 90

2,72 to 3,25 3,05 to 3,65 3,90 to 4,10

5,9 to 7,0 6,3 to 7,7 7,8 to 9,0

100 150 175 200

3,90 to 5,15 5,45 to 7,25 6,95 to 7,25 6,95 to 7,25

7,8 to 10,7 10,4 to 15,2 13,2 to 15,2 13,2 to 15,2

Table 2 — Clout nails


1 2 3

Length D H 32 and greater 2,72 to 2,88 8,2 to 9,1


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4.1.5.2 Nuts, bolts and threaded rods 4.1.5.2.1 Nuts shall comply with the requirements of SANS 1700-14-1, SANS 1700-14-2, SANS 1700-14-3 or SANS 1700-14-4. 4.1.5.2.2 Bolts shall comply with the requirements of SANS 1700-7-1, SANS 1700-7-2 or SANS 1700-7-3, and shall have a shank that is 20 mm longer than the total thickness of the timber which is to be bolted together. NOTE Cup-head bolts or carriage bolts have square shanks which might damage the timber. 4.1.5.2.3 Where bolts cannot be used, galvanized threaded rods with a yield stress equivalent to that of the bolts specified in 4.1.5.2.2, shall be used. 4.1.5.3 Washers Washers shall have the dimensions given in table 3.

Table 3 — Washer sizes


1 2 3

Washer size Bolt diameter Square Round

Up to 8 25 × 25 × 2,4 25 × 2,4

Up to 12 36 × 36 × 6 36 × 3,6

Up to 20 60 × 60 × 6 60 × 6

Exceeding 20 75 × 75 × 6 75 × 6 4.1.5.4 Nail plates, toothed connectors, split rings and shear plates Nail plates, toothed connectors, split rings and shear plates shall comply with the requirements of SANS 10243. 4.1.5.5 Hangers and hurricane clips 4.1.5.5.1 Unless otherwise specified in the specification data, metal punched plate hangers and hurricane clips shall have a zinc galvanized coating of 275 g/m2, or have an equivalent corrosion resistance, and shall bear a mark which readily identifies the manufacturer or supplier. 4.1.5.5.2 Unless otherwise specified in the specification data, hangers and hurricane clips shall be tested by an accredited testing laboratory to demonstrate that, when bolted or nailed through predrilled or prepunched holes into structural softwood (pine) members, they can transfer, across the joint, a permissible load of not less than the following without slippage occurring: a) hurricane clips: 1,2 kN b) hangers: 4,0 kN


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4.1.5.6 Masonry anchors Unless otherwise specified in the specification data, metal masonry anchors shall be of the expanding type, be corrosion resistant and have a diameter and length of not less than 10 mm and 45 mm, respectively, and shall be installed in accordance with the manufacturer’s instructions. Such anchors, when embedded in grade 20 concrete for standard test purposes, shall have a safe working load in shear of not less than 2,5 kN certified by the manufacturer. Such certification shall be substantiated by test report certificates from an accredited certification body. 4.1.5.7 Special connectors Special connectors shall be in accordance with the requirements specified in the scope of work. NOTE Pole cradles, which are used to affix a horizontal pole against a masonry or concrete wall, are, in terms of this part of SANS 2001, special connectors. 4.2 Drawings Unless reference is made, in the specification data, to applicable national standards for the design and detailing of roof assemblies, drawings of the roof assembly shall be provided showing all member sizes and connection details in sufficient detail to enable the roof to be constructed and, where required, permanently braced. 4.3 Jointing of timber members 4.3.1 General 4.3.1.1 All joints shall be close-fitting and members shall not have to be forced into position as a result of warp (bow, twist, spring or cup). 4.3.1.2 Trusses shall be assembled in plane, and in such a way as to avoid damage to any of the members. 4.3.2 Bolted and nailed connections 4.3.2.1 Unless skew nailing is required, nails shall be driven in at right angles to the grain of the timber and to such a depth that the heads are flush with the timber surface. Where skew nailing is required, the skew nail shall not be closer than 30 mm from the edge of the member through which it is driven. 4.3.2.2 In hardwood, nails shall be driven into predrilled holes that have a diameter of between 0,5 and 0,8 times the nail diameter. 4.3.2.3 Hurricane clips and hangers shall either be nailed in each hole with 32 mm long wire clout nails, or be bolted with a single bolt that has a diameter of 8 mm for hurricane clips or 12 mm for hangers. NOTE 75 mm nails should not be used for hurricane clips and hangers, as these might cause excessive damage to the fibres of the timber. 4.3.2.4 Holes drilled through timbers to accommodate bolts shall not have a diameter that exceeds the bolt diameter by more than 1 mm.


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4.3.2.5 Holes shall be drilled at right angles to the joints. Where timber-to-timber connections are to be made, the components shall be clamped together before drilling. NOTE The use of templates for marking the positions of bolts is recommended. 4.3.2.6 All bolts used to connect structural members shall be installed with washers under both the head and the nut. Nuts shall be tightened so that the washers just bite into the surface of the timber. Bolts shall be of sufficient length so as to allow at least one full thread to project from the nut when tightened. 4.3.2.7 In pole members, bolts shall not be installed within one pole diameter of a cracked or split end. Nails shall not be placed in cracks in pole members. 4.3.2.8 Nuts shall be so tightened that the members fit closely. If necessary, nails shall be tightened again after the timber has reached its equilibrium moisture content. 4.3.2.9 Bolts and nails in members other than poles shall not be located closer to the edge of members than the distances shown in figure 1. Bolts and nails in poles shall be located along the centre line of the poles. 4.3.2.10 Nails and bolts shall be spaced at least 20 mm and 50 mm, respectively, away from each other. 4.3.3 Nail-plate connectors 4.3.3.1 Nail-plate connectors shall be as specified in the specification data, and be pressed into timber using either a mechanical pressing device or a carpenter’s hammer, depending upon their design. 4.3.3.2 When making nail-plated trusses, timber that has defects, such as wane and dead knots in the connector plate contact area, shall not be used unless the size of the connector plate is increased by 25 mm in both the length and the breadth of the original nail-plate dimensions to compensate for the nails that have become ineffective at that defect in the member. 4.3.3.3 The average gap between any two adjacent members in nail-plated connections shall not exceed 1,5 mm. 4.3.3.4 The difference in thickness between adjacent members shall not exceed 1,0 mm. 4.3.3.5 Nail-plate connectors shall be evenly embedded to ensure full penetration of all teeth without damage to the timber or fastener. 4.3.3.6 Nail-plate connectors, when fixed, shall not project beyond the outer edge of the members which they join together. The lower edge of any nail-plate connector located over a point of support to a trussed rafter shall be at least 5 mm away from the lower edge of the member in contact with the support. 4.3.4 Toothed connectors, split rings and shear plates Toothed connectors, split rings and shear plates shall be installed in accordance with the requirements of SANS 10243.


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a) Minimum nail spacing

b) Minimum bolt spacing

Figure 1 — Nail and bolt spacing in joints between timber members 4.4 Installation of masonry anchors Masonry anchors shall be installed in accordance with the manufacturer’s instructions. 4.5 Reshaping and resawing of members 4.5.1 When treated softwood members are reshaped or resawn, the end grain of the exposed ends shall be painted with a suitable timber preservative. 4.5.2 When poles are reshaped or resawn to a different length, the end grain of the exposed ends shall, a) in the case of softwood poles, be painted with a suitable timber preservative, and b) in the case of hardwood poles, be treated with a class W preservative and be provided with a

new nail plate that covers at least 35 % of the surface area of the end.


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4.6 Installation of roof trusses, rafters and purlin beams 4.6.1 General 4.6.1.1 Trusses, rafters and purlin beams shall, unless otherwise specified in the scope of work, be supported on a) wall plates, in accordance with the requirements of table 4, or similar flat bearing surfaces which

are levelled and positioned so as to ensure that the ends of such members are vertically aligned, or

b) hangers, twice bolted to walls with masonry anchors. 4.6.1.2 Where ends are not built into walls or supported by hangers, the ends shall be skew nailed into such bearings on each side by means of two 100 mm long ordinary wire nails. Nails shall preferably not be driven through nail plates. 4.6.1.3 Hangers shall either be nailed in each hole with 32 mm long clout wire nails or be bolted with a single 12 mm diameter bolt. 4.6.1.4 Site alterations to trusses or rafters may only be made if such alterations do not compromise their design intent or performance in use (or both). NOTE A competent person, as defined in SANS 10400, should review the suitability of site alterations to trusses or rafters. 4.6.1.5 Unless otherwise specified in the scope of work, all rafters and roof trusses shall be tied down to the supporting walls by means of the roof anchorages which are built into the supporting walls or columns. Galvanized steel straps shall be nailed to the roofing members by means of not less than eight clout nails (see figure 2). Galvanized steel wires shall be tied together. 4.6.1.6 Trusses and rafters shall not be overstressed during transportation, storage and erection. Impregnated timber shall be protected, as necessary, and shall be so handled that the impregnated shell is not broken through and the wood is not damaged in any way that might reduce the effectiveness of the preservative. NOTE For more information on the storage of timber members and trusses on site, see annex C.

Table 4 — Wall plate sizes

1 2

Truss support span S Cross section of plate

m mm

S < 10 38 × 76

10 < S < 15 38 × 114

S > 15 38 × 152


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NOTE A double strand of 2,4 mm diameter galvanized steel wire may be used in place of hoop-iron straps in light roofs where the trusses are at centres that do not exceed 750 mm and in all heavy roofs (see SANS 10400). a Four 32 mm clout nails (min.) (for a heavy tiled roof) or eight 32 mm clout nails (min.) (for a light sheeted

roof) or three 75 mm nails.

Figure 2 — Holding-down detail 4.6.2 Erection of trusses 4.6.2.1 Preparatory work 4.6.2.1.1 Before trusses are erected, the area to receive trusses shall be checked to ensure that the wall plates are level and that the holding-down wires or the hoop-iron strap has been built into the supporting structure at the correct centres. 4.6.2.1.2 The positions of the trusses on the wall plates shall be marked in accordance with the drawings and the specified truss centres. Trusses adjacent to a gable shall be positioned between 50 mm and 100 mm from the inside of the gable wall. NOTE A gap of between 50 mm and 100 mm facilitates the plastering of the inside of the gable wall at ceiling level. 4.6.2.2 Lifting of trusses 4.6.2.2.1 Wherever possible, trusses shall be handled and lifted in an upright or vertical position. If the trusses are to be moved horizontally, suitable intermediate support shall be provided to prevent lateral distortion of the trusses, which can lead to possible damage. NOTE Timber trusses, correctly aligned in their upright position and properly supported by bracing, purlins or roof sheeting, are very strong structural components. They can, however, be easily damaged when subjected to excessive lateral bending due to improper handling and lifting.


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4.6.2.2.2 When trusses are lifted by hand, care shall be taken to prevent excessive lateral bending when sliding them over walls and when tipping them upright on the walls (see figure 3). Where cranes are used, the following rigging shall be used to lift single trusses and groups of trusses into position: a) for trusses that have a span of up to 6 m, a single pick-up point shall be used to pick up not more

than three trusses as shown in figure 4; b) for trusses that have a span of between 6 m and 9 m, two belt slings with hooks or a looped sling

shall be used such that the distance between slings is approximately half the length of the truss and the angle between the two slings is less than 60° as shown in figures 5 and 6;

c) for trusses that have a span of between 9 m and 18 m, a spreader bar that is sufficiently rigid so

as not to bend sideways when the truss is lifted, and is between two-thirds and three-quarters the length of the truss, shall be used with slings at suitable intervals as shown in figures 7 and 8; and

d) for trusses that have a span of between 18 m and 30 m, an inflexible "strongback" secured to the

truss at intervals of 3 m or less, that has a length of at least two-thirds of the truss span, shall be used as shown in figures 9 and 10.

4.6.2.2.3 When using rigging, care shall be taken not to damage the timber and connectors at the pick-up points. NOTE Canvas slings are preferable to chain slings. 4.6.2.2.4 Multiple trusses that comprise identical trusses joined side by side should preferably be assembled on the ground to form a complete unit. Where a multiple truss is too heavy to lift or handle, it may be assembled in situ. 4.6.2.2.5 Once trusses have been lifted into position, they shall be checked for any damage that might have occurred during the lifting and handling operations. A damaged truss shall be removed or repaired so that the truss as erected does not compromise its design intent or performance in use (or both). NOTE A competent person, as defined in SANS 10400, should assess any damage to the trusses and review the suitability of the repairs. 4.6.2.3 Temporary bracing 4.6.2.3.1 The first truss shall be lifted into position onto the wall plates and temporarily braced to the ground or wall plate (see figure 11) with grade 5 timber that has a minimum size of 76 mm × 38 mm or poles with a diameter of not less than 100 mm, or supported against the gable end so that the truss is both straight and vertically plumb. Thereafter, the next few trusses may be lifted into position at their correct spacing and fixed in position with temporary runners and bracing (see figure 12). 4.6.2.3.2 The erected trusses shall be lined up, levelled, plumbed and straightened before the installation of the permanent web and rafter bracing. Thereafter, the remainder of the trusses may be erected, ensuring that temporary bracing and runners are fixed as the erection of trusses proceeds.


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4.6.2.3.3 If it is necessary to insert wedges or packs between the wall plate and the bottom chord, wedges shall be installed from both sides. Where required, packs or wedges should be made of rectangular blocks of timber at least the same width as the wall plate. NOTE The diagonal members brace the truss against lateral movement so that it does not change its shape. Bracing ensures that ● trusses erected correctly will remain vertical, ● the top and bottom chords will remain straight, ● truss spacing will remain constant, and ● compression members do not buckle. 4.6.2.4 Permanent bracing Upon completion, all trusses shall be checked for straightness, plumbness and that they are level, and shall be adjusted, as necessary, on the wall plate. The remainder of the permanent bracing shall be fixed. 4.6.3 Erection of rafters and purlin beams Rafters and purlin rafters or purlin beams (or both) shall be erected straight and plumb at the required slope (see figure 13). Where 50 mm × 228 mm rafters are used, the timber shall be free from any serious warping which might affect the straightness and plumbness of the rafters when fixed in position. 4.7 Installation of battens and purlins 4.7.1 Battens and purlins shall be continuous over at least three rafters (i.e. two rafter spacings) and shall be fixed to every rafter that they cross. Battens of size 38 mm × 38 mm shall be nailed to rafters with 75 mm wire nails, and battens of size 38 mm × 50 mm shall be set on edge with 90 mm wire nails. Purlins shall be fixed to rafters in accordance with figure 14. Care shall be taken not to split any of the members during the nailing process. 4.7.2 The ends of battens and purlins shall be sawn square and butt-jointed centrally over the rafter member so as to provide suitable bearing and fixing. Alternatively, battens may be spliced in close proximity to rafters by means of nailed splices or connector plates, as shown in figure 15. 4.7.3 Joints in battens shall be arranged so that not more than one batten in any three is joined (spliced) on any one rafter (see figure 16(c)). 4.7.4 Purlins shall be spliced in accordance with figure 16. Splices shall be located in close proximity to rafters and shall be staggered so that there is not more than one splice in three consecutive purlins. Purlins and rafter splices shall not be located within 1,5 m from the gable ends. 4.8 Ceiling assembly Brandering of size 38 mm × 38 mm required to support gypsum plasterboard, fibre-cement board or similar board shall be securely spiked to the supporting timbers with 75 mm wire nails at centres that do not exceed 450 mm. Cross brandering shall be cut in between the longitudinal brandering and skew nailed to the same, using 75 mm wire nails at centres that do not exceed 900 mm.


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Figure 3 — Lifting trusses by hand

Figure 4 — Rigging for triangular trusses that have a span of up to 6 m

Figure 5 — Rigging for parallel chord trusses that have a span of up to 9 m


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Figure 6 — Rigging for triangular trusses that have a span of up to 9 m

Figure 7 — Hoisting parallel chord trusses that have a span of 9 m to 18 m


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Figure 8— Support for a triangular truss that has a span of 9 m to 18 m

Figure 9 — Attachment of strongback to a parallel chord that has a span of 18 m to 30 m


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Figure 10 — Attachment of strongback to triangular trusses that have a span of 18 m to 30 m

Figure 11 — First truss in position


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a) Installation of first permanent vertical cross bracing

b) Replacement of temporary bracing

c) Spacing of bracing

Figure 12 — Temporary bracing of trusses


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Figure 13 — Typical arrangement of purlin rafter/beam

a) Tied connection b) Hurricane clip connection NOTE For aesthetic purposes, the hurricane clip connections are usually used at eaves overhangs whilst wireis often used for connections hidden by ceilings.

Figure 14 — Purlin to rafter connection detail


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a) Batten splice (general practice) b) Nailed timber splice

c) Connector plate splice a Joints in battens shall be staggered so that not more than one in three is spliced on any one rafter.

Figure 15 — Splicing of battens


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a) Block purlin splice

NOTE Fix hurricane clips on one side only.

b) Plated purlin splice

Splices shall not be within 1,5 m of the gable ends and shall be staggered so that not more than one in three is spliced on any one rafter.

c) Purlin splices between trusses

Figure 16 — Typical layout of purlin splices


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5 Compliance with the requirements 5.1 Determination of moisture content The moisture content of all timber except poles, where it is a requirement of the specification data that the moisture content be measured, shall be determined in accordance with the relevant methods given in SANS 1783-1. Tests to determine the moisture content of poles shall be carried out in accordance with the relevant methods given in SANS 457-2 or SANS 457-3. 5.2 Permissible deviations 5.2.1 The permissible deviations (pd) in individual timber members and in trusses shall be in accordance with tables 5 and 6. 5.2.2 The bow between purlins or battens shall not exceed Lp/100 or 30 mm maximum, where Lp is the purlin/batten spacing, in millimetres. 5.2.3 Battens shall be aligned to within a tolerance of ± 10 mm in 4 m and shall be fixed to a spacing tolerance of ± 5 mm. 5.2.4 Rafters, purlin beams and purlins shall be spaced within a tolerance of ± 30 mm.

Table 5 — Permissible deviations of timber members

1 2

Description Permissible deviation Spring 5 mm per 3 m length Bow 10 mm per 3 m length Twist 1 mm per 25 mm width per 3 m length

Table 6 — Permissible deviations in trusses

1 2

Permissible deviation Description mm

a) Overall horizontal dimensions ± 15 b) Overall vertical dimensions ± 25 c) Difference between overall vertical and horizontal dimensions of similar trusses in a continuous roof

10

d) Deviation of erected truss apex from the vertical for rise of • 1 m • 2 m • 3 m • 4 m or more

10 15 20 25

e) Bow after erection ± 10


26

Annex A (normative)

Preparation of specification data associated with this part of SANS 2001 for inclusion in the scope of work

Specification data form an essential part of this part of SANS 2001; without such data, requirements are incomplete. The format for the specification data has been developed to be compatible with the requirements in table D.1 of SANS 10403:2003. The specification data should be incorporated in the scope of work as shown in table A.1.

Table A.1 — Incorporating this part of SANS 2001 in the scope of work

1 2 3

TOPIC ASPECT COMMENTARY DESCRIPTION OF THE WORKS CONSTRUCTION Works specifications Applicable part(s) of

SANS 2001 The following parts of SANS 2001 and associated specification data are applicable:

1) SANS 2001 ….. 2) SANS 2001 ….. The associated specification data are as follows:

Essential data: The requirements for .….…. are ….….

Specification data pertaining to SANS 2001 …..

The requirements for …..…. are ….….

Variations: 1) 2)

Additional clauses: 1)

Applicable national and international standards

Particular/generic specifications


27

Develop the specification data based on the contents of table A.2.

Table A.2 — Specification data associated with this part of SANS 2001

1 2 3 Guidance notes Specification data associated with this

part of SANS 2001 Clause number Consideration

Essential data 4.1.2.1 Omit if shown in the drawings. Laminated/softwood timber joists shall be

grade …….... and have a cross section of ......……

Alternatively, state that laminated/softwood roofing timbers shall be of the type and cross section given in a stated standard.

All softwood timber shall be treated against the effects of rot, fungus and insect attack.

4.1.2.5 Omit if softwood timber shall only be treated in the specified magisterial districts.

Roofing poles shall comply with 4.1.3.1 Omit if shown in the drawings. SANS 457-2 (softwood) or SANS 457-3 (hardwood).

Alternatively, state that laminated/softwood roofing timbers shall be of the type and cross section given in a stated standard.

Metal punched plate hangers and hurricane clips shall …..

4.1.5.5.1 Amend requirements for hangers and clips if requirements of 4.1.5.5.1 are unsuitable. Omit if requirements of 4.1.5.5.1 are suitable.

Certification of safe working loads shall be tested by ...…

4.1.5.5.2 Omit if certification is done by accredited testing laboratory. Identify other suitable testing bodies.

Metal masonry anchors shall be of the expanding type, be corrosion resistant and have a diameter and length of not less than …….......

4.1.5.6 The masonry anchors as specified in 4.1.5.6 have sufficient strength to support roofs where no access is provided other than that necessary for cleaning and repair, and which have a span that does not exceed 8 m.

Amend the specifications where design requires greater strength to support long span joists.

The roof trusses and bracing details shall be in accordance with the requirements of .........

4.2

or

Omit if prefabricated trusses shall be used or if trusses that are outside the scope of a national standard shall be fabricated.

Softwood rafters in accordance with the requirements of ………… shall be placed at centres that do not exceed .......……. m

Alternatively, select appropriate option and reference standard.

or The standard bracing details for trusses contained in ……… shall be used.

Nail plates shall be installed by means of a mechanical pressing device/carpenter’s hammer.

4.3.3.1 Select the means by which the nail plates shall be installed. A carpenter’s hammer shall be used to apply nail plates applied to the ends of cut poles.

The moisture content of 10 % of all timber brought to the site shall be confirmed.

5.1 Omit if not a requirement.

Variations State variations, if any. Additional clauses State additional requirements, if any.


28

Annex B (normative)

Areas that fall within municipal boundaries

where softwood timber shall be treated

Figure B.1 — Section of KwaZulu-Natal Province (new municipal boundaries)

SAN

S 2001-CT2:2009

Edition 1.1

29

Figure B.2 — Section of Western Cape Province (new municipal boundaries)

SAN

S 2001-CT2:2009

Edition 1.1

30

Figure B.3 — Section of Eastern Cape Province (new municipal boundaries)


31

Figure B.4 — Section of Northern Cape Province (new municipal boundaries)


32

Annex C (informative)

Storage of timber members and trusses on site

C.1 SANS 1921-1 establishes general performance requirements for the storage and protection of materials on site, namely that materials shall be stored and protected in such a manner that any deterioration, distortion, damage or contamination does not impair their performance when incorporated into the works. C.2 Timber elements should be so stored that they are not a) exposed to climatic conditions more severe than those to be encountered in the finished

structure, or b) subjected to prolonged exposure to the weather or to conditions conducive to fungal or insect

attack, or c) crushed or otherwise damaged. C.3 Trusses should be so stored that they are not in contact with the ground, and in such a way that they retain their manufactured shape. Trusses should preferably be stored vertically, on beams located at the points of support assumed in the design, and with suitable props to maintain them in the vertical position. When stored horizontally, they should be supported on bearers located at every joint and stacked neatly on top of each other. C.4 If trusses are covered for prolonged periods to protect them from the weather, the covering material should also provide for ventilation to the timber.

Bibliography SANS 1921-1, Construction and management requirements for works contracts – Part 1: General engineering and construction works.

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Documents

SOUTH AFRICAN NATIONAL STANDARD Construction works Part ... · ISBN 978-0-626-22646-6 SANS 2001-CT2:2009 Edition 1.1 SOUTH AFRICAN NATIONAL STANDARD Construction works Part CT2: Structural