GENERAL
Cross-reference
General: Read with A90 General technical requirements.
Preservative treatment: Read with Z12 Preservative and fire retardant treatment. Mortar: Read with Z21 Mortars.
PRODUCTS
Fibre cement slates
Standard: To BS EN 492.
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Type: NT (nonasbestos).Battens, counterbattens, ridge/ hip fixing battens and verge battens
Timber: To BS 5534, clause 4.12.1.
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Permissible characteristics and defects limits: Not to exceed limits in BS 5534, annex C.•
Moisture content at time of fixing and covering: 22% (maximum).Preservative treatment: To British Wood Preserving and Damp-proofing Association Commodity Specification C8.
Fasteners
Nails:
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Aluminium nails: To BS 1202-3.•
Copper nails: To BS 1202-2.•
Steel nails: To BS EN 10230-1 as appropriate for specified type.Hip irons
Standard: To BS 5534 , clause 4.16.1.
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Material: Galvanized steel.Mortar bedding and pointing
Mortar: 1:3 cement:sand.
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Plasticizing admixtures: Permitted.•
Bond strength: Provide resistance to uplift to BS 5534.Slating underlay
Reinforced bitumen sheet: To BS 5534, Annex A. Breathable membrane: Agrément certified.
EXECUTION
Slating generally
Standard: To applicable parts of BS 5534.
General: Fix slating and accessories to make the whole sound and weathertight at earliest opportunity. Setting out: To true lines and regular appearance, with neat fit at edges, junctions and features. Fixings for slating accessories: As recommended by slate or accessory manufacturer.
Gutters and pipes: Keep free of debris. Clean out at completion.
Removing existing slating
General: Carefully remove slates, battens, underlay, etc. with minimum disturbance of adjacent retained slating. Undamaged slates: Set aside for reuse.
Underlay
Handling: Do not tear or puncture. Laying: Maintain consistent tautness.
Vertical laps: 100 mm wide (minimum), coinciding with supports and securely fixed.
Fixing: Fix with galvanized steel, copper or aluminium 20 x 3 mm extra large clout head nails. At penetrations of pipes and components: Select from:
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Proprietary underlay seals or•
Cut underlay accurately to give a watertight fit. Ventilation paths: Do not obstruct.Counterbattens
Fixing:
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On rigid sarking: Through rigid sarking into rafters at 300 mm (maximum) centres.•
On rafters: Into rafters at 300 mm (maximum) centres.Battens
Setting out: Align parallel to ridge in straight horizontal lines to gauge of the tile. Align on adjacent areas. Batten length (minimum): Sufficient to span over three supports.
Joints in length: Square cut, butt centrally on supports. Joints must not occur more than once in any group of four battens on any one support.
Unsupported underlay laps between battens: Provide additional battens. Fixing: Each batten to each support. Splay fix at joints in length.
Slate fixing
Setting out: Lay slates to a half lap bond with not more than 5 mm gaps. Align tails.
Ends of courses: Use extra width slates to maintain bond and to ensure that cut slates are as large as possible. Do not use half slates.
Extra width slates: Use additional fixings as recommended by slate manufacturer.
Top courses: Cut top two slate courses as necessary to maintain gauge. Head-nail top course. Fixings for slates: Nails/ Rivets recommended by slate manufacturer.
Mortar bedding and pointing
Weather: Do not use in wet or frosty conditions or when imminent.
Preparation of slates and accessories to be bedded or pointed: Coat relevant surfaces with a suitable bonding agent. Preparation of concrete and clay tile accessories to be bedded: Wet and drain surface water before fixing.
Appearance: Finish neatly as work proceeds and remove residue.
Roof slating edges, junctions and features generally
Fittings and accessories: Proprietary, not improvised.
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Exposed fittings and accessories: Match slate colour and finish. Cut slates: Only where necessary, to give straight, clean edges. Flashings: Fix with or immediately after slating. Dress down neatly.Fire separating walls
Separating wall: Completely fill space between top of wall and underside of tiles with mineral wool quilt to provide fire stopping. Boxed eaves: Completely seal air paths in plane of separating wall with wire reinforced mineral wool, 50 mm thick (minimum), fixed to rafters. Cut carefully to shape to provide fire stopping.
Integrated grilles/ trays for ventilated eaves
Execution: Fix to carry underlay, form drip into gutter and provide free passage of air over insulation.
Undercourse and first course slates: Fix with tails projecting 50 mm over gutter or to centre of gutter, whichever dimension is the lesser.
Separated grilles/ trays for ventilated eaves
Execution: Fix to carry underlay, form drip into gutter and provide free passage of air over insulation.
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Underlay support: Continuous to prevent water retaining troughs.•
Gutter: Dress underlay or underlay support tray to form drip into gutter.Undercourse and first course tiles: Fix with tails projecting 50 mm over gutter or to centre of gutter, whichever dimension is the lesser.
Unventilated eaves
Gutter: Dress underlay or underlay support tray to form drip into gutter. Underlay support: Continuous to prevent water retaining troughs.
Undercourse and first course slates: Fix with tails projecting 50 mm over gutter or to centre of gutter, whichever dimension is the lesser.
Dry (closed) verge
Underlay: Carry over full width of verge. Project 30 mm to turn down behind closer. Slating battens: Carry over underlay to abut verge roof batten.
Verge roof batten for closer fixing: 38 x 19 mm (minimum).
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Position: From eaves to ridge.Verge edge batten for deep closer side fixing (not required for standard closed verge): 38 x 32 mm (minimum).
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Position: From eaves to ridge.Dry (closed) verge with undercloak
Underlay: Carry 50 mm onto outer leaf of gable wall and bed on mortar. Undercloak: Fibre cement slate or sheet.
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Position: Over underlay, level with underside of tiling battens, sloping towards verge.•
Bedding: On mortar identical to that used in gable walling. Slating battens: Carry over undercloak to abut verge roof batten. Verge roof batten for closer fixing: 38 x 19 mm (minimum).•
Position: From eaves to ridge.Verge edge batten for deep closer side fixing (not required for standard closed verge): 38 x 19 mm (minimum).
Mortar bedded verge with bedded undercloak
Underlay: Carry 50 mm onto outer leaf of gable wall and bed on mortar. Undercloak: Fibre cement slate or sheet.
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Position: Over underlay, level with underside of slating battens, sloping towards verge.•
Projection beyond face of wall: 38–50mm.•
Bedding: On mortar identical to that used in gable walling.Slating battens: Carry onto undercloak and finish 100 mm from verge edge. Verge closure battens: Fix between ends of slating battens.
Verge slates:
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Bedding: Flush with undercloak on 75 mm wide bed of mortar.•
Pointing: Struck weathered profile, 5 mm back from verge slates.•
Fixing: Do not displace or crack mortar.Mortar bedded verge with nailed undercloak
Underlay: Carry over full width of verge. Undercloak: Fibre cement slate or sheet.
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Position: Over underlay, level with underside of slating battens, sloping towards verge.•
Projection beyond face of wall: 38–50mm.•
Fixing: Nailed.Slating battens: Carry onto undercloak and finish 100 mm from verge edge. Verge closure battens: Fix between ends of slating battens.
Verge slates:
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Bedding: Flush with undercloak on 75 mm wide bed of mortar.•
Pointing: Struck weathered profile, 5 mm back from verge slates.•
Fixing: Do not displace or crack mortar.Hips
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Underlay: Lay courses over hip. Overlap 150 mm (minimum). Dry capped hips:•
Roof slates: Cut and fix closely at hip.•
Dry hip cappings: Shape bottom hip cappings neatly to align with corner of eaves. Mitred hips:•
Laying: Cut double width slates and fix to form a straight, close mitred junction.•
Soakers: Interleave with mitred slates. Fix by turning down over head of mitred slates. Mortar bedded hips:•
Slates: Cut and fix closely at junction.•
Bedding: Continuous to edges, solid to joints, in mortar.•
Fixing: Where rigid masonry walls support or abut hip, secure hip tiles within 900 mm of such walls to hip rafters or supplementary hip battens with nails/ wire ties or screws.•
Bottom hip tiles: Shape neatly to align with corner of eaves and fill ends with mortar and slips of tile finished flush.•
Hip irons: Fix to hip rafter or hip batten with two (minimum) zinc coated steel screws.Valleys
GRP valleys:
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Underlay: Lay as recommended by GRP valley manufacturer.•
Roof slates: Cut double width slates adjacent to valley to fit neatly. Metal valleys:•
Underlay: Cut to rake. Dress over tilting fillets to lap onto metal valley. Do not lay under metal.•
Roof slates: Cut double width slates adjacent to valley to fit neatly. Mitred valleys:•
Underlay: Lay strips 600 mm wide (minimum) centred on valleys. Overlap with general roof underlay.•
Mitred slates: Cut double width slates and fix to form a straight, close mitred junction.•
Soakers: Interleave with mitred slates. Fix by turning down over head of mitred slates.Abutments
Underlay: Turn up 100 mm (minimum) at abutments. Side abutment:
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Abutment slates: Cut as necessary. Fix close to abutments.•
Soakers: Interleave with abutment slates. Fix by turning down over head of abutment slates. Top edge abutments:•
Top course slates: Fix close to abutments.Dry capped ridge
Underlay:
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Sealed ridge: Lay courses over ridge. Overlap: 150 mm (minimum).•
Ventilated ridge: Provide air gap at apex.Top slating battens: Position and fix to suit fixing of ridge cappings. Dry ridge cappings:
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Fixing: Screw to top slating battens.•
Joints in length: Face away from prevailing wind. Apply sealant strip.Mortar bedded tile ridge
Underlay: Lay courses over ridge. Overlap: 150 mm (minimum). Ridge tiles:
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Bedding: In mortar continuous to edges, solid to joints.•
Fixing: Where rigid masonry walls support or abut ridge, secure ridge tiles within 900 mm of such walls to ridge boards or supplementary ridge battens with nails/ wire ties or screws.•
Gable end ridge tiles: Fill ends with mortar and slips of tiles finished flush.Dry capped mono-ridge
Underlay:
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Sealed ridge: Lay 100 mm (minimum) over mono-ridge.•
Ventilated ridge: Provide air gap at apex.Top slating battens: Position and fix to suit fixing of mono-ridge cappings. Dry mono-ridge cappings:
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Fixing: Screw to top slating battens.•
Joints in length: Apply sealant strip.Mortar bedded tile mono-ridge
Underlay: Lay 100 mm (minimum) over mono-ridge. Mono-ridge tiles:
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Bedding: In mortar continuous to sloping edges, solid to joints.•
Fixing: Secure vertical faces to ridge fixing battens with screws/ nails.•
Gable end mono-ridge tiles: Fill ends with mortar finished flush.Vertical slating edges/ junctions
Bottom edges:
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Slating base work: Fix timber tilting fillet to support bottom course of slates in correct vertical plane. Fix flashing to tilting fillet.•
Underlay: Dress over flashing.•
Undercourse and bottom course slates: Fix with tails neatly aligned. Top edges:•
Top slate courses: Fix under abutment and make weathertight with flashings dressed down 150 mm (minimum). Side abutments:•
Slating base work: Chase abutment wall and insert stepped flashing.Flashing: Return 75 mm (minimum) behind slating, overlapping underlay and battens. Turn back to form a vertical welt.