south african national standard - thatch regulations€¦ · this standard covers the design of the...

ISBN 978-0-626-32636-4 SANS 10407:2016Edition 2.1

SOUTH AFRICAN NATIONAL STANDARD

Thatched roof construction

WARNING This document references other

documents normatively.

Published by SABS Standards Division 1 Dr Lategan Road Groenkloof Private Bag X191 Pretoria 0001Tel: +27 12 428 7911 Fax: +27 12 344 1568 www.sabs.co.za SABS

Licensed exclusively to FIDDLER™ ROOFING PRODUCTS.Copying and network storage prohibited.

SANS 10407:2016 Edition 2.1

Table of changes

Change No. Date Scope

Amdt 1 2016 Amended to modify the design requirements for poles.

Foreword

This South African standard was approved by National Committee SABS/TC 098/SC 04, Structural and geo-technical design standards – Design of timber structures, in accordance with procedures of the SABS Standards Division, in compliance with annex 3 of the WTO/TBT agreement.

This document was approved for publication in October 2016.

This document supersedes SANS 10407:2015 (edition 2).

A vertical line in the margin shows where the text has been technically modified by amendment No. 1.

This document is referenced in the Local Government: Municipal Systems Act, 2000 (Act No. 32 of 2000).

Annex A forms an integral part of this document. Annex B is for information only.

Compliance with this document cannot confer immunity from legal obligations.

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Contents

Page Foreword 1 Scope .................................................................................................................................. 3 2 Normative references .......................................................................................................... 3 3 Definitions ........................................................................................................................... 4 4 Requirements ...................................................................................................................... 5 5 Structural design ................................................................................................................. 13 6 Chimneys ............................................................................................................................ 17 7 Accuracy ............................................................................................................................. 17 8 Fire safety ........................................................................................................................... 17 9 Quality assessment of a roof ................................................................................................ 17 Annex A (normative) Thatching grass and reed types and their locations ............................ 18 Annex B (informative) Servicing of thatch roofs ..................................................................... 20 Bibliography ........................................................................................................................... 23

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Thatched roof construction

1 Scope This standard covers the design of the supporting roofing structure and installation of thatch on roofing structures. NOTE SANS 10400-L covers the design of roof structures, SANS 10400-T covers fire protection requirements, and SANS 10400-V covers chimney requirements. SANS 2001-CT2 covers the construction of the structural timberwork in the roof.

2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. 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. SANS 457-3, Wooden poles, droppers, guardrail posts and spacer blocks – Part 3: Hardwood species. SANS 820, Mild steel nails. SANS 1083, Aggregates from natural sources – Aggregates for concrete. SANS 1288, Preservative-treated timber. SANS 1707-2, Sawn eucalyptus timber – Part 2: Brandering and battens. SANS 1783-4, Sawn softwood timber – Part 4: Brandering and battens. SANS 2001-CT2, Construction works – Part CT2: Structural timberwork (roofing). SANS 10005, The preservative treatment of timber. SANS 10155, Accuracy in buildings. SANS 10183-1, Adhesives for wood – Part 1: Terminology. SANS 10183-2, Adhesives for wood – Part 2: Requirements for structural applications.

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SANS 10400-B, The application of the National Building Regulations – Part B: Structural design. SANS 10400-K, The application of the National Building Regulations – Part K: Walls. SANS 10400-L, The application of the National Building Regulations – Part L: Roofs. SANS 10400-T, The application of the National Building Regulations – Part T: Fire protection. SANS 10400-V, The application of the National Building Regulations – Part V: Space heating. SANS 50197-1/EN 197-1, Cement – Part 1: Composition, specifications and conformity criteria for common cements.

3 Definitions For the purposes of this document, the following definitions apply. 3.1 acceptable acceptable to the authority administering this standard, or to the parties concluding the purchase contract, as relevant 3.2 batten small sawn square or rectangular timber member, fixed parallel to the line of the eaves, at right angles to the rafters, and onto which thatch is fixed 3.3 butt end lower, cut end of a stem 3.4 competent person person who, by virtue of the possession of a recognized relevant professional qualification, or who, by applicable knowledge, training and experience, has successfully demonstrated the ability to solve or resolve problems relating to the subject matter 3.5 deviation difference between the actual (i.e. measured) dimension or position and the specified dimension or position 3.6 dress action of tapping the butt ends of thatch or thatching reed upwards with a leggatt to produce the correct surface slope 3.7 lath small round timber member, fixed parallel to the line of the eaves, at right angles to the rafters, and onto which thatch is fixed 3.8 leggatt wooden tool, shaped like a bat with a grooved or drilled-out surface, used to dress the thatch or thatching reed stems into place

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3.9 overlay over thatch second layer of thatch over original layer 3.10 specification data data, provisions and variations that are in accordance with SANS 2001-CT2, and applicable to a particular contract or works 3.11 spray layer layer immediately above the thatching battens or laths, where the underside will often be exposed in a room 3.12 suitable capable of fulfilling or having fulfilled the intended function, or fit for its intended purpose 3.13 supporting wall structural wall wall that functions as a load-bearing wall suitable to support a thatched roof 3.14 sway rod that is parallel to the lath in the thatch layer tie and binds material to the lath to secure the thatch 4 Requirements 4.1 Materials 4.1.1 Thatching grass and reeds 4.1.1.1 General 4.1.1.1.1 Thatching materials, unless otherwise specified in the specification data given in SANS 2001-CT2 for thatching types in locations, shall comply with the list of most commonly used grasses and reeds in South Africa and their geographical locations, as given in annex A. 4.1.1.1.2 Thatching materials shall be of a type that has a history of successful use as a roof covering in the relevant geographical locations. 4.1.1.1.3 Thatching materials shall be harvested at the time when growth has stopped or the seed has ripened and dispersed. 4.1.1.1.4 Any application to the thatch and all fire retardant systems used shall not affect the lifespan of the thatching material nor change the nature of the material prematurely. 4.1.1.1.5 Thatching materials shall be stored such that a) the stem surface is not physically damaged, b) the bundles are clear of the ground, and c) the bundles are not unduly exposed to moisture and the sun.

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4.1.1.2 Thatching grass 4.1.1.2.1 Common or fine thatching grass (Hyperenia hirta and Hyperenia filipendula) for use shall a) have a cut length of not less than 0,8 m (measured from the butt end, and including the tips of

seed ends), b) have a minimum diameter and maximum diameter at the butt end of 1,2 mm and 2,5 mm,

respectively, c) be suitably straight (cut above the first node), d) be free of loose material, e) be workable, f) not be cut in the growing season, g) be fully grown and matured, and h) be free of seed when cut. 4.1.1.2.2 Yellow and red Tamboekie (measuring a minimum of 1,0 m), or coarse thatching grass (Hyperthelia dissoluta) shall a) have a cut length that is not less than 1,0 m (measured from the butt end, and including tips of

seed ends), and b) comply with the requirements given in 4.1.1.2.1(b) to 4.1.1.2.1(h) (inclusive). 4.1.1.3 Cape reed Thatching reed (Thamnochortus species) shall a) have a minimum cutting length of 1,0 m (measured from the butt end, and including tips of seed

ends), b) have a minimum diameter of 1,2 mm and a maximum diameter of 5 mm at the butt end, c) be acceptably straight, d) be workable, e) not be cut in the growing season (to ensure that the nodes are tight), f) be mature and ligneous, g) be free of sand and silt, and h) be sun-dried for at least 7 d before bundling.

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4.1.1.4 Water reed Water reed (Phragmites australis or Phragmites communis) shall a) have a minimum length and maximum length of 1,5 m and 1,8 m, respectively (measured from

the butt end, and including tips of seed ends), b) have a minimum diameter of 3 mm and a maximum diameter of 7 mm at the butt end, c) be suitably straight, d) have a taper towards the plume, e) be workable, f) have no secondary growth, g) not be cut in the growing season (to ensure that the nodes are tight), h) be mature, and i) be free of sand and silt. 4.1.2 Timber 4.1.2.1 General 4.1.2.1.1 Pressure treated timber should preferably be machined prior to treatment. Where pressure treated timber used out of ground contact is fabricated (for example, cross-cut to length, or otherwise machined), exposed surfaces of untreated heartwood shall be liberally coated with the same or similarly suitable remedial or supplemental brush-on preservative. 4.1.2.1.2 In the case of hardwood poles treated with waterborne preservatives for example copper-chromium-arsenic (CCA), the binding or anti-split nail plates as given in SANS 457-3 shall be re-applied to the cut and exposed ends following the application of the remedial preservative to prevent the development of post treatment end checks. 4.1.2.1.3 The timber poles specified shall meet the material requirements given in SANS 457-2 or SANS 457-3, as relevant. Timber shall be treated in accordance with SANS 10005. Laths and battens shall meet the requirements given in SANS 1288, SANS 1707-2 and SANS 1783-4, as relevant. 4.1.2.2 Rafter poles Poles for use as structural elements shall have a diameter of at least 100 mm, measured at the thin ends. 4.1.2.3 Upright columns Upright columns shall be spaced at no more than 3,5 m apart. 4.1.2.4 Battens and laths 4.1.2.4.1 Battens or laths shall be continuous over at least three rafters (i.e. a spacing of two rafters), and shall be fixed to every rafter that is crossed. Battens shall be nailed to rafters with 75 mm wire nails. Care shall be taken not to split any of the members during the nailing process.

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4.1.2.4.2 The ends of battens shall be sawn square and butt-jointed centrally over the rafter member. Joints in battens shall be arranged so that not more than one batten in any three is joined on any one rafter. 4.1.2.4.3 The battens shall have a minimum nominal diameter of 38 mm × 38 mm or 38 mm × 50 mm and the laths shall have a minimum top diameter of 25 mm, and be spaced in accordance with the requirements for the respective types of thatching material used (see table 1). 4.1.2.4.4 The bow between battens shall not exceed 30 mm. 4.1.2.4.5 Battens shall be fixed to a spacing tolerance of ± 25 mm.

Table 1 — Batten or lath spacing

1 2 3

Batten or lath position Minimum length of thatch or reed Maximum batten centres

mm mm

Second from the bottoma – 200

Third from the bottomb – 200

Second from the top (ridge) – 150

All other battens and lathsb 800, 1 200, 1 500 200, 300, 350

a The maximum batten centre is measured from the end of the rafter. b The maximum batten centre is determined by dividing the length of the thatch by four.

4.1.3 Nails Nails shall a) be round nails that comply with SANS 820, and b) have a minimum diameter of 2,8 mm. 4.1.4 Pole cradle (hanger) Pole cradles or similar connectors shall be approved by the competent person as being able to carry the loads acting on them. 4.1.5 Sway Sways, if used, shall consist of either a) galvanized wire with a minimum diameter of 3,15 mm, or b) Cape reed in bundles of at least 10 mm. 4.2 Thatch layers 4.2.1 Thickness of thatch layers The thickness of the finished layer for the respective thatching materials shall be in accordance with the requirements given in table 2.

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4.2.2 Servicing of a thatch roof The thickness of a second layer termed as either an overlay or an over thatch, shall be in accordance with table 2 (see columns 2, 3 and 5 of table 2). If a second layer is found it shall first be removed before the overlay or over thatch is applied (i.e. there shall never be more than two layers of thatch on the roof structure). NOTE Annex B gives further information on the servicing of thatch roofs.

Table 2 — Material provisions at time of construction

1 2 3 4 5 6

Species

Cover over sways/ binding

Stem/butt diameter

Thickness of thatch

layer

Minimum mass of thatch

layer/m2

Minimum design mass

of thatch layer

min. mm mm mm kg kg

Common or fine thatching grass (Hyparrhenia hirta and Hyparrhenia filipendula)

70 1,2 to 2,5 175 45 105

Yellow and red (Tamboekie) or coarse thatching grass (Hyperthelia dissoluta)

80 2,5 to 5 200 55 120

Thatching reed (Thamnochortus species)

80 1,2 to 5 180 72 120

Water reed (Phragmites australis or Phragmites communis)

100 1 to 7 300 70 125

4.2.3 Thatch cover over sways The thatch cover over the sways depends on the type of material used and the thickness of the layer, and should be at least 40 % of the thickness of the specific layer. The minimum cover, however, shall not be less than that given in table 2. 4.3 Laying 4.3.1 Thatching shall commence from a verge at the bottom of the roof and shall be laid parallel to the rafters or trusses. 4.3.2 The thatching bundles at the end of the hip plane shall run parallel to the hip rafters. The full thickness of the thatch shall be maintained around the bend of the hip. 4.3.3 Unless otherwise specified in the specification data, the thickness and minimum mass per square metre of the finished layer for the respective thatching materials shall be in accordance with the requirements given in table 2. 4.4 Binding 4.4.1 The binding or fastening of the thatch onto the battens shall be in accordance with the method of thatching agreed upon, and not be spaced more than 110 mm apart.

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4.4.2 The materials used shall be tar-treated sisal twine, stainless steel or galvanized wire, with a diameter of between 0,9 mm and 1,2 mm. 4.5 Valleys 4.5.1 Thatch valleys shall be formed by gradually orientating the thatching bundles in each layer from the normal vertical alignment direction to one that is parallel to the valley. Additional material shall be laid in the valley to provide extra thickness to prevent water penetration into the thatch layer and to provide a gradual sweep rather than a sharp bend. 4.5.2 Valley liners are permissible, using 0,5 mm galvanized sheeting, 0,7 mm aluminium sheeting, or 0,5 mm copper valley liners. 4.6 Ridges 4.6.1 General 4.6.1.1 The ridge construction shall be as specified in the scope of work. 4.6.1.2 Ridges shall be of an acceptable material for ridge construction works. They shall not include material that leaves a void below the ridge and the top of the apex of the thatch layer (see figure 1 and figure 2). 4.6.1.3 The bundles of ridging grass or reed shall be bent over the ridge and securely anchored onto the opposite two topmost battens on both sides of the ridge with sways, using the same method of binding or fastening used on the rest of the roof. 4.6.2 Sand-cement ridges 4.6.2.1 The sand-cement ridge capping shall be a minimum of 40 mm thick (one part common cement to four parts of sand), and shall a) extend at least 750 mm from the ridge down each side of the thatching, b) be laid on a single polyolefin membrane layer, c) be reinforced with a galvanized metal lath or galvanized wire mesh, with a cover to the lath not

less than 20 mm, and d) be suitably shaped and thickened at the ridge as shown in figure 2. 4.6.2.2 Lapping of joints in the polyolefin membrane shall not be less than 200 mm. 4.6.2.3 The materials in sand-cement ridges shall comprise a) common cement that complies with SANS 50197-1, b) sand that complies with the relevant requirements given in SANS 1083, c) galvanized wire mesh with a thickness not less than 0,8 mm and an opening that does not

exceed 25 mm, d) polyolefin membranes that have a thickness of not less than 250 µm, and that comply with the

relevant requirements given in SANS 10183-1 and SANS 10183-2, for a type C sheeting, and e) potable water.

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Figure 1 — Typical sand and cement ridge construction 4.6.3 Fibreglass ridge installation 4.6.3.1 Ridgepole construction shall be either single ridge or double ridge. 4.6.3.2 On both ridge constructions, the last two laths shall be spaced at 150 mm above the last line of thatch. This line shall also be stitched down to secure the thatch in two places. The last line of thatch shall be fixed with a 3,15 mm galvanized wire sway. Where the 3,15 mm wire joins, allow wires to overlap by at least 200 mm. 4.6.3.3 The last line shall not be cut. The top ends of the grass shall be folded over the ridgepole and fixed to the opposite side, covering the thatch on the hip end of the roof. The lath that was installed 300 mm above the last line of thatch shall be used to stitch down the opposite last layer of thatch. This shall be done from both sides of the roof. 4.6.3.4 The thatch on the hip end of the roof shall be folded over the ridge pole and tied to the ridge pole, and be stitched to the pole by means of a hook needle. 4.6.3.5 After the completion of the requirements given in 4.6.3.2 to 4.6.3.4, all the thatch shall be stitched to the ridgepole with a hook needle. NOTE This process is necessary to ensure that the last line of thatch does not slip out under the fibreglass ridging. This process will also prevent birds from pulling out the thatch. 4.6.3.6 Two holes, each of 2 mm diameter, shall be punched or drilled into the bottom 50 mm reinforced part of the fibreglass ridging. The holes in the ridge shall not be spaced further than 200 mm apart. NOTE 1,5 mm galvanized wire should be threaded through the two holes while the ridging is still on the ground.

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4.6.3.7 Before the ridge is installed, the thatch and twine fixings shall be re-checked to ensure that they are tight, and that the last lines of thatch are straight and in place. 4.6.3.8 In areas where birds are a problem, bird mesh with a hole diameter of no more than 25 mm shall be placed over the last line of thatch and shall extend at least 900 mm from the centre of the ridge down to the overhang. This bird mesh should also be stitched to the ridgepole to hold it in place, before installing the fibreglass ridge over. 4.6.3.9 Ridging should be used in sections that are as long as possible, to reduce the use of joins. Fibreglass ridging can be made in lengths of up to 9 m. 4.6.3.10 The ridging can now be fitted to the roof, and the following shall be taken into consideration when fitting the ridges: a) Ridging shall be placed loosely in its correct position and shall be tightly stuffed with loose

bundles of grass. b) Care shall be taken to ensure that the ridging fits tightly to the top ridge pole, as this would

eliminate any further voids. c) After the ridge has been stuffed, the ridge can be pulled down onto the thatch. Every third wire

shall be pulled tight and tied to the last lath. The wire shall be stitched through the thatch at an angle to eliminate water from following the fixing through the thatch. By fixing it to the last lath, it ensures that the fixing is under the fibreglass ridging and cannot be affected by water.

d) Gable-end covering shall be purpose made, and shall enclose and protect the last two lines of

thatch. These two lines of thatch shall also be double stitched and preferably be covered with bird mesh under the fibreglass covering. When the ridge is aligned and level, the remaining wire fixings can be tied down. The fixings shall then be covered with a small piece of chopped strand matt and resin from a supplied join kit, to avoid the formation of rust.

4.6.3.11 Where the fibreglass ridging joins it shall overlap a minimum of 75 mm. 4.6.3.12 The joins shall be aligned by the thatcher. If the thatcher has ensured that the top of the ridging fits snugly to the ridgepole, the ridging will align automatically as it will follow the contour of the roof structure. 4.6.3.13 The area where the ridging is joined shall be sanded lightly to assist with bonding. 4.6.3.14 Resin shall be applied to the joining area and a layer of chopped strand matt shall be placed over the resin. A second layer of resin shall be applied to the chopped strand matt. 4.6.3.15 All ridging shall be covered with an acrylic based waterproof paint and this paint shall be re-applied to the areas which have been joined. If the join is still visible it can be sanded and the water based acrylic paint can be re-applied. 4.6.3.16 Fibre glass ridging shall have a girth of not less than 1 500 mm. 4.6.4 Grass ridges The bundles of ridging grass shall be bent over the ridge and securely anchored onto the two topmost battens with sways and a suitable method of binding or fastening.

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Figure 2 — Typical fibreglass ridge construction

5 Structural design 5.1 General Structural design shall be in accordance with SANS 10400-L. 5.2 Slope 5.2.1 Roofing, in terms of slope design, shall be in accordance with SANS 10400-L. 5.2.2 The design of the roof shall be such that it allows for the free drainage of water. 5.2.3 Care shall be taken to ensure that an individual stem has a downward gradient. 5.3 Design requirements 5.3.1 The design of the roof supporting structure shall be a) a rational design, in accordance with SANS 10400-B, or b) in accordance with the deemed-to-satisfy requirements given in 5.3.2 to 5.3.11 (inclusive) for

pole structures, and the requirements given in SANS 10400-L. 5.3.2 Thatched roofs constructed of poles shall a) be of gable-to-gable construction, b) be without any hips, valleys or dormer windows, c) have a pitch of 45°, and d) have a clear span that does not exceed 6 m. The construction shall be in accordance with figure 3, figure 4 and table 2, and shall be constructed in accordance with the requirements given in this standard. 5.3.3 Poles shall comply with the requirements given in SANS 457-2 (softwoods), or SANS 457-3 (hardwoods), and shall be treated in accordance with the requirements given in SANS 10005. Poles which have cracked or split pole ends within one pole diameter location of a bolt position shall not be incorporated into such structures.

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5.3.4 When poles are re-shaped or re-sawn to a different length, the end grain of the exposed ends shall be remedially treated (see 4.1.2). A new anti-split nail plate complying with the material requirements given in SANS 457-3, and that covers at least 60 % of the surface area of the pole end, shall be nailed to the end to prevent and minimize excessive cracking. Amdt 1 5.3.5 Laths used in thatched roof construction shall a) have a minimum diameter of 25 mm, b) comply with the preservative-treatment requirements given in SANS 1288, and c) be spaced in accordance with the requirements given in this standard. 5.3.6 Pole rafters shall have a clear span in accordance with table 3. 5.3.7 Pole trusses and rafters shall be tied down to the supporting walls and columns by means of galvanized steel wires, which are built into the walls in accordance with the requirements given in SANS 10400-K. 5.3.8 All poles shall be measured at the thin end. 5.3.9 Upright pole columns shall be spaced at no more than 3,5 m centres, and not be less than 175 mm in diameter. 5.3.10 Pole ring beams shall be placed on top of upright columns and not bolted to the side of columns. 5.3.11 No ring beam shall be less than 150 mm in diameter. 5.3.12 The sizes of members for thatched roofs constructed of poles shall be in accordance with table 4.

Table 3 — Maximum clear spans for gum pole rafters

1 2 3 4

Type of roof covering Diameter of pole

Maximum clear span

m

Rafter spacing

mm 750 mm 900 mm

Tiled roofs that have a pitch of less than 26°

100 to 125 2,7 2,5

125 to 150 3,5 3,3

150 to 175 4,4 4,1

Sheeted roofs that have a pitch of less than 26°

100 to 125 3,8 3,5

125 to 150 4,8 4,5

150 to 175 5,8 5,5

The maximum mass of the tiles or slates, including battens or purlins, shall not exceed 65 kg/m2.

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Dimensions in millimetres

Key M Member

Figure 3 — Elevation of truss for thatch roofing in gable-to-gable rectangular buildings that have a clear span that does not exceed 6,0 m

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Dimensions in millimetres

Key M Member T Truss R Rafter NOTE The diameter of the pole is 100 mm to 125 mm.

Figure 4 — Plan of truss for thatch roofing in gable-to-gable rectangular buildings that have a clear span that does not exceed 6,0 m

Table 4 — Sizes of members for thatched roofs constructed of poles

1 2

Member Size

mm

Rafters 100 to 125 for truss clear spans ≤ 6 m

Ridge brace 100 to 125

Ridge collar 100 to 125

King post 100 to 125

Bottom chord 125 to 150 (tie beam)

Rafter brace 125 to 150

NOTE Pitch = 45°.

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6 Chimneys The design and construction of chimneys shall be in accordance with SANS 10400-V.

7 Accuracy The degree of accuracy, when erecting the pole structures, shall be in accordance with SANS 10155, and the following provisions: a) the maximum vertical deviation of the king post shall be 10 mm/1 000 mm height; b) the maximum horizontal deviation of tie-beams and rafters shall be 50 mm/1 000 mm; c) the maximum deviation of poles measured in the central position between the connections shall

not exceed 25 mm; and d) bolt-end distances and spacing shall be in accordance with the provisions of 7(c).

8 Fire safety Fire safety shall be in accordance with SANS 10400-T.

9 Quality assessment of a roof A competent person shall inspect and assess the roof after erection to ascertain whether it is acceptable in terms of aesthetics, workmanship and structure, and in accordance with good practice, as well as the requirements given in this standard.

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Annex A (normative)

Thatching grass and reed types and their locations

A.1 General A.1.1 The Southern African grasses that are commonly used and their geographical locations are listed in table A.1.

Table A.1 — Grass types

1 2 3

Scientific name Common name Geographical location

Hyparrhenia hirta Common thatching grass South Africa (widespread) Natal Berg area

Hyperthelia dissoluta Yellow thatching grass or Tamboekie coarse thatching grassa

Limpopo Province, Northern KwaZulu-Natal, Swaziland

Hyparrhenia dregeana – Natal Midlands and Berg area

Hyparrhenia filipendula Fine thatching grass KwaZulu-Natal, Zululand and coastal regions, Gauteng and Mpumalanga

Thamnochortus insignis Cape thatching reed or Dekriet Albertinia and Riversdale districts of Cape Province

Thamnochortus erectus Cape summer reed Cape coastal regions

Thamnochortus specigerus Dekriet or thatch reed Cape coastal regions

Chondropetalum tectorum Western Cape thatching reed Cape area (widespread)

Phragmites australis Norfolk reed or swamp grass, Umhlanga grass

South Africa (widespread)

a Tamboekie grass is used in rural areas for thatching. Coarse varieties where the stalks are thicker than 4 mm in diameter are not, however, considered suitable for thatching.

A.1.2 Thatch grass is usually cut from mid-June to August, after growth has stopped and the first hard frost has killed the leaves. In areas where no frost occurs, grass is usually cut when the grass plumes no longer have seed. A.1.3 Harvested thatching material is round in bundles of diameter as given in table 1. The thatching material shall be vigorously shaken to dislodge all loose material and, if necessary, combed with a side-rake or sickle to remove leaves from the stems and to clear superfluous weed growth. Thereafter, the material shall be bundled and tied for transporting. A.1.4 The diameter of bundles shall meet the provisions given in table A.2.

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Table A.2 — Bundle provisions at time of construction

1 2 3

Species

Diameter of the

bundle

Approximate mass of the

bundle

mm kg

Common or fine thatching grass (Hyparrhenia hirta and Hyparrhenia filipendula)

125 0,8 to 0,9

Yellow and red (Tamboekie) or coarse thatching grass (Hyperthelia dissoluta)

125 1,3 to 1,5

Thatching reed (Thamnochortus species)

75 1,1 to 1,3

Water reed (Phragmites australis or Phragmites communis)

200 4,5 to 5,4

A.2 Preparation before thatching A.2.1 Thatch or thatching reed used in a spray layer shall be combed with a suitable comb to ensure that the stalks are clean before installation. NOTE A comb may be made by driving 75 mm wire nails into a horizontal pole. Bundles of thatch or thatching reed should be placed on top of the comb and pressed down so that the stalks are separated by the nails. The bundle should then be pulled through the comb from the top to the bottom end. A.2.2 Each bundle of thatching or thatching reed shall be butted against a butting board or level ground to ensure that the butt end is even and all sharp ends are blunted before installation.

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Annex B (informative)

Servicing of thatch roofs

B.1 An unqualified thatcher should not comb a roof. The user needs to understand the technical detail of a thatch roof before allowing an unqualified thatcher to comb a roof. Every combing process unless properly done, reduces the cover over the sway (i.e. the functional thickness of a roof and therefore the lifespan of the roof). For functional thickness see figure B.1.

B.2 The correct procedure is to inspect the general length of the thatch or reed; if found long enough, the next step is to pull down the thatch layers (see figure B.1).

B.3 The binding twine then needs to be tightened on the underside of the roof (see figure B.2). Only then can the combing process begin. NOTE It is advisable that this process be successfully completed and that no shortcuts are taken.

Figure B.1 — Thatching roof thickness

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B.4 Figure B.2(a) shows the incorrect thickness of the thatch which shortens the lifespan of a thatched roof. Figure B.2(b) shows the correct thickness of the thatch which ensures a longer lifespan for a thatched roof. The lifespan of the roof has a direct bearing on the length of the stem below the twine.

Drg.942a

a) Thickness of the thatch fora shortened life span

b) Thickness of the thatch fora longer life span

Figure B.2 — Lifespan of a thatched roof

B.5 The lifespan of a thatched roof can be controlled during the thatching process by ensuring that the correct thickness is maintained. When using common thatching grass, care should be taken when exceeding a thickness of 300 mm as it could be prone to wind damage.

B.6 Figure B.3(a) shows the method of pulling down the thatch layers. Figure B.3(b) shows the method of tightening the twine after the pulling down of the outer layer of bundles.

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Drg.942b

a) Pulling down of the thatch layersof a thatched roof

b) Twine tightening on a thatched roof

Figure B.3 — Thatching maintenance

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Bibliography BOU/E9806:1998, A guide to good thatching practice. Published by the Division of Building and Construction Technology, CSIR, P.O. Box 395, Pretoria, 0001. SANS 10142-1, The wiring of premises – Part 1: Low-voltage installations. SANS 10160 (all parts), Basis of structural design and actions for buildings and industrial structures. SANS 10163-1, The structural use of timber – Part 1: Limit-states design. SANS 10163-2 (SABS 0163-2), The structural use of timber – Part 2: Allowable stress design. SANS 10313, Protection against lightning – Physical damage to structures and life hazard. SANS 62305-3/IEC 62305-3, Protection against lightning – Part 3: Physical damage to structures and life hazard.

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