Roofing and Cladding. ALTERNA NT-slate APPLICATION INSTRUCTIONS 11

Transcription

1 Roofing and Cladding ALTERNA NT-slate APPLICATION INSTRUCTIONS 11 DOUBLE COVER SLATE LAYING SYSTEM 1. GENERAL Throughout the world slates have been traditionally laid on millions of roofs in a double cover configuration. This method of weatherproofing a building can be used on roofs with a simple or complex geometry with a wide variety of finishes. This method of laying slates can be used on roof covering and wall cladding on new and refurbishment projects. 1 These application instructions replace all previous editions. ETERNIT reserves the right to change these instructions without prior notice. Readers should always make sure to consult the most recent version of this document. The instructions in this document are non-exhaustive. The guarantees are only applicable if the application instructions are followed. Ask advice from ETERNIT in case of different applications. ETERNIT, Technical Service Center 1/21

2 It is called "double cover" because over the entire roof area at least two slate thicknesses occur. (At end laps there are three layers of material). In general the slates should be installed in accordance with NBN which states the minimum roof pitch of 25 (measured on the slate surface) and provides guidance on the end lap of slates depending on the roof pitch. Slates are usually fixed to a roof having the following construction: An under-roof sheeting to protect against rain, fine snow or dust ingress as well as making the entire roof more windproof. This sheeting also makes the whole roof less vulnerable to storm damage. Wooden counterbattens are then fixed through to the rafters following the slope of the roof. Slate battens are secured horizontally to the roof, spaced a predetermined distance apart. Slates are fixed to these battens with special hook and where necessary two additional nails. This roofing method can be used regardless of the direction of the prevailing wind. Technical data The NBN B stipulates the following overlaps according to pitch and climatological exposure: Roof pitch Climatological exposure Vertical lap (*) a >= mm 30 >= a < 70 normal severe 90 mm 110 mm 25 >= a < 30 (**) 110 mm 130mm (*) The minimum slate size is a multiple of the overlap: - slate length = 3 x overlap - slate width = 2 x overlap (**) Note: An under-roof is strongly recommended in all other cases but is compulsory for all pitches between 25 and 30 with an overlap of 110 mm. ETERNIT, Technical Service Center 2/21

3 Fig. 1 shows the relationship between the pitch of the roof expressed in: - degrees ( ) - percent (%) - cm/m - roof surface slope length per meter horizontal projection Fig. 1 ETERNIT, Technical Service Center 3/21

4 The tables below give the necessary data for each slate size according to the overlap: Size 40 x 27 Overlap (mm) Number/m² 20,86 23,55 25,17 27,03 Batten gauge (mm) Weight/m² (kg) 17,9 20,3 21,6 23,2 Battens (m/m²) 5,71 6,45 6,90 7,41 Size 45 x 32 Overlap (mm) Number/m² 15,43 17,15 18,16 19,29 Batten gauge (mm) Weight/m² (kg) 17,6 19,6 20,7 22,0 Battens (m/m²) 5,00 5,56 5,88 6,25 Size 60 x 40 (*) Overlap (mm) Number/m² 9 9,71 10,10 10,53 Batten gauge (mm) Weight/m² (kg) 18,50 18,4 19,2 20,0 Battens (m/m²) 3,63 3,93 4,08 4,26 (*) must always be fixed with a stainless steel hook, diameter 3 mm. Size 60 x 32 Size 60 x 32 Overlap (mm) Number/m² 11,22 12,10 12,60 13,13 Batten gauge (mm) Weight/m² (kg) 18,29 19,73 20,54 21,41 Battens (m/m²) 3,63 3,93 4,08 4,26 ETERNIT, Technical Service Center 4/21

5 Installation instructions The slates are installed on a wooden support structure consisting of horizontal battens. Ideally, under-roof sheets are laid on the rafters and trusses before the counter battens are attached (Fig. 2). The lath wood quality and its permanent protection against attack by fungus and insects must comply with the local standards. Fig Lay lines 2. Battens 3. Counterbattens 4. Under-roof sheet 5. Eaves slate 6. Roof boards The minimum sizes of the battens are based on the centre to centre distance between support points: - spacing less than 400 mm : 19 mm x 38 mm - spacing 400 mm to 500 mm : 26 mm x 38 mm - spacing 500 mm to 600 mm : 32 mm x 38 mm Wood quality and treatment of the counterbattens is identical to that for the battens. Counterbattens are a minimum of 20 mm thick to allow any water ingress to run down the under-roof sheet and into the gutter. A roof board is placed at the foot of the roof, level with the ridge. It should be 4 mm thicker than the battens to compensate for the thickness of the missing slates. The maximum permitted overhang of the eaves slates over the edge of the first batten is 50 mm. The distance between the bottom edge of the roof board and the top edge of the following batten is therefore equal to a minimum of the batten distance + overlap - overhang. Horizontal lines are then marked on the roof or façade at distances equal to the batten gauge as set out in the tables above. The battens are placed on these lines over the whole surface. Any unevenness must first be removed in order to ensure the stress-free, solid fixing of the battens. ETERNIT, Technical Service Center 5/21

6 Once the battens are in place, vertical lines are marked on them, half a slate + 2 mm apart. The first row of slates are eaves slates whose length in a horizontal roof foot is equal to the batten gauge + the overlap. These slates must be secured by two nails. Hooks are fixed between the slates of the first eaves course to receive the next slate course. These hooks and slates are laid so that their bottom edge coincides with the lowest edge of the eaves slates. The top edge of this second course rests upon the next batten. The centres of the joints between the slates in this second course are set half a slate + 2 mm apart in relation to the first course. All other courses are laid in the same way as the second course. Fixing For the fixing of the slates copper or stainless steel hooks (Fig. 3 and Fig. 4) as well as copper nails (Fig. 5) are used. To fix the slate size 60x40, always a 3 mm thick stainless steel hook is used. They can be installed using a slater s hammer. Fig. 3 Fig. 4 Fig. 5 Photo 1. ETERNIT, Technical Service Center 6/21

7 2. DETAIL PRINCIPLES Eaves detailing The bottom edge of the roof finish has already been discussed (Fig. 2). Care must always be taken to ensure that the water discharges into the gutter and, more particularly, that any water ingress can run down the under-roof into the gutter. The gap between the under-roof and the outer roofing material must be closed by a special eaves closure. This prevents nest building and the accumulation of leaves in this space, which is likely to interfere with the water running down the under-roof. Ridge Photo 2. Eave The top-course slates are always held in place by two nails and a hook. The ridge can be covered with: - fibre cement accessories (half round ridge, roll top ridge, or internal socketed ridge) - lead flashing and rectangular slate finish (Strackort). Photo 3. Half round ridge Photo 4. Ridge with internal socket ETERNIT, Technical Service Center 7/21

8 After both roof slopes have been completely covered, the ridge cappings are fixed to a ridge rafter by means of two copper nails and a copper ridge clip. They are laid against the prevailing wind direction, with a minimum overlap of 70 mm. Fig. 6. Half round ridge Fig. 7. Roll top ridge Fig. 8. Ridge with internal socket Fig. 9. Ridge clip Type of ridge piece Total length (mm) Net covering length (mm) Number per m (pcs) Standard included angle Half round ,03 - Roll top , Internal socket , ETERNIT, Technical Service Center 8/21

9 For the ridge treatment with the lead flashing and slates (Strackort) a number of slates must be cut and drilled as shown in the drawing in Fig. 10. The subsequent installation steps are shown in Fig. 11. The Strackort slates are held in place by two nails and a copper hook that is first opened out and then closed back. 12,9 slates per linear meter are required for this ridge treatment. Fig. 10 Fig. 11: Installation sequence for Strackort ridge finishing. Photo 5. ETERNIT, Technical Service Center 9/21

10 Hip Fig. 12 Hips can be covered in exactly the same way as the ridges using fibre cement half round ridge, roll top ridge, internal socketed ridge, or the Strackort method. If the pitch of both roof slopes adjacent to the hip is the same, the hip can be finished with: - slant-cut slates (Fig. 13) - close mitred hip (Fig. 14) Fig. 13. Hip with slant cut slates 1. Counter batten 2. Batten 3.Lead flashing Photo 6. Hip with slant-cut slates Photo 7. Close mitred hip ETERNIT, Technical Service Center 10/21

11 Fig. 14. Close mitred hip 1. Roof board 2. Batten 3. Under roof 4. Counter batten 5. Lead flashing 6. Eaves closure ETERNIT, Technical Service Center 11/21

12 Valley gutter The valley gutter can be made in open or close mitred form. - Open valley gutter (Fig. 15) A zinc interior gutter is laid along the valley line under the under-roof sheeting of both slopes. Roof boards are placed on the counter battens along both sides of the valley. A metal or plastic gutter is then laid on this bed. The slates are cut parallel to the valley, but overlap the gutter edges by at least 80 mm. Fig. 15 Photo 8 1. Gutter 2. Under-roof 3. Roof boards - 4. Interior Gutter Fig. 16: Open valley gutter 1. Roof boards 2. Interior gutter 3. Under-roof 4. Gutter ETERNIT, Technical Service Center 12/21

13 - Close mitred valley gutter (Fig. 17) To provide a seal, a V-shaped zinc strip is fitted under the under-roof sheets along the centerline of the valley gutter. Two roof boards of the same thickness as the battens are placed either side of the valley. Full slates are cut obliquely to follow the line of the valley. The weather-seal is provided by the insertion of a lead soaker, with a developed width of minimum 200 mm, between the slates. Fig. 17 Photo 9 1. Roof boards 2. lnterior gutter 3. Under-roof 4. Lead slab Fig. 18. Lead slab for the close mitred gutter L = batten gauge O = overlap ETERNIT, Technical Service Center 13/21

14 Chimneys Any water running down the roof slope is collected in a V-shaped metal flashing and directed either side of the chimney. This metal flashing is extended upslope to where the under-roof sheet can overlap. The slate roofing is continued to the bottom of the chimney. The foot connection with the chimney is obtained using a metal flashing covering the slates with the same vertical overlap as the slates. The metal flashing is worked between the slates at the sides of the chimney. The slates cover this flashing at least 100 mm. A further metal profile is laid on the upper part of the chimney and covered by the slates. The metal parts on all sides of the chimney are then covered with another flashing cut into the joints of the brickwork. Photo 10. Photo 11. Photo 12. Verge At the verge full or half slates should always be used. The offcut slate pieces are worked further up into the courses. All slates or slates pieces along the verge must be held in place by two nails. Photo 13. Verge finishing ETERNIT, Technical Service Center 14/21

15 Some possible construction techniques for verges are: - verge with lead flashing (Fig. 19) - verge with metal profile (Fig. 20) - verge with cladding slates (Fig. 21) Fig. 19 Fig. 20 Fig 21 ETERNIT, Technical Service Center 15/21

16 Dormer windows Proprietary dormer windows are supplied with all necessary flashing pieces. The frame sill is connected to the slates by means of a metal flashing. The side slates (or part of slates) are then fixed; a metal flashing is inserted between each edge slate. Finally, the frame head is finished using a metal flashing delivered with the window. Any water running over the under-roof is sent over the V-shaped metal run-off plate along the side of the dormer window. This plate is fitted above the roof opening, where the under-roof sheets overlap. Fig 22 Photo 14. Dormer window ETERNIT, Technical Service Center 16/21

17 Abutment to brickwork Abutments are made in the same way as side connections on chimneys. Photo 15. Abutment to brickwork Ladder hooks Ladder hooks are always held in place by screws fixed in a rafter. Water tightness is ensured by means of an upper and lower lead flashing. Photo 16. Ladder hook ETERNIT, Technical Service Center 17/21

18 Gutter let into the roof slope Fig Eave closure 2. Zinc gutter 3. Patinized zinc Mansard Fig Under-roof 2. Zinc 3. Patinized zinc ETERNIT, Technical Service Center 18/21

19 Ventilators They are made of plastic and are used to allow the free passage of air through the roof. They are mostly used to ventilate bathrooms, kitchens,... This model is unsuitable for the removal of hot air or combustion gases. These parts are easily inserted into the slate roof. Photo 17. Universal ventilator slate ETERNIT, Technical Service Center 19/21

20 3. ROOF COMPOSITION Fig. 25 shows a general view of a roof composition. The roof shell made up of slates, battens & counter battens has already been dealt with in detail. We now turn to the under-roof, insulation and interior finish. We intend to show that the entire roof construction should be considered as a whole, with all components and materials being compatible with each other, as an incorrect construction in one part may create problems in other areas. Fig Under-roof 2. Thermal insulation 3. Air cavity 4. Wiring cavity 5. Interior finish Under-roof The under-roof is made of fibre cement sheets. See the chapter on Flat sheets for more detailed assembly instructions. Extensive tests at the University of Louvain have shown that a vapor permeable underlay, like fibre cement, is less vulnerable to condensation problems. If the underlay can absorb and transmit vapor through to the void below the slates, formed by the counterbattens/battens, it can be effectively removed from the roof construction (drained or evaporated). Other less permeable underlays may allow condensation to form on the underside and drip onto the insulation or build up in the roof construction. The unique combination of properties of fibre cement sheets makes it the ideal under-roof material. ETERNIT, Technical Service Center 20/21

21 Insulation It is generally recommended to install the insulation continuously. In other words, there should be no gaps or breaks between the interior finish and the insulation, the insulation and the under-roof, and under no circumstances at all between individual insulation sheets. These gaps cause air currents to circulate around the insulation sheets, causing considerable heat loss as well as carrying moisture into the under- roof. Interior finish The first and foremost requirement with regards to the interior finish is the air-tightness. It therefore follows that open joints and drill-holes are not permitted. If, however, ducts for cables etc. are foreseen, the interior finish must be split into an air barrier and a finish layer (Fig. 25). The wiring and any appliances can then be housed in the intermediate wiring cavity. The vapor barrier: WTCB Publication TV 134 expressly states that no specific requirements are laid down for roof vapor barrier in Climate Classes I to III provided the under-roof is constructed using fibre cement sheets (vapor permeable under roof sheets). A specific roof construction study is required in all cases for Climate Class IV (e.g., swimming pools, kitchens, bakeries,). ETERNIT nv, Roofing Division Kuiermansstraat 1, B-1880 Kapelle-op-den-Bos * info.dak@eternit.be website: RPR Brussels VAT BE ETERNIT, Technical Service Center 21/21