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7.2.19 Fixing tiles and slates
Coverings shall be suitably fixed to protect the building from weather. Issues to be taken into account include:
- eaves, ridge and hip tiles
- verges
- mortar
- mansard roofs and dormers.
Careful setting out will improve the finished appearance of the roof, help avoid problems such as unequal overhangs, and reduce excessive tile cutting at abutments, chimneys and similar obstructions.
When installing coverings:
- clay tiles that do not meet the dimensional and geometric requirements given in BS EN 1304 should not be laid at pitches less than 40°
- joints between tiles and slates should be slightly open, which provides some flexibility in setting out and should help to avoid tile cutting (single lap interlocking tiles have a tolerance of approximately 3mm at the joint)
- double tiles, tile-and-a-half or half tiles can be used, when available from the manufacturer (to avoid the use of small sections of cut tiles). Alternatively, where the tile manufacturer provides guidance, small sections of single lap tile can be bonded to full tiles
- the bottom edges of double-lapped slate and plain tile roofs should be finished with an under-eaves course.
Table 21: Pitch, gauge and lap
| Type or tile | Gauge | Minimum headlap | Minimum permissible pitch (°) |
|---|---|---|---|
| Plain (double lap) | Maximum 1/3 length lap | 65mm generally for clay tiles 75mm in severe exposure conditions | 35 (clay) 35 (plain concrete) |
| Concrete (single lap interlocking) | Comply with the manufacturer’s recommendations | 75mm or to the manufacturer’s recommendations | 30⁽²⁾ |
| Slates (double lap) | Maximum 1/3 length lap | 54mm⁽¹⁾ minimum, increased with lower pitch and severe exposure conditions | 20 subject to headlap |
Notes
1. For pitches greater than 45° and less than 75° in sheltered and moderate exposure zones only.
2. For pitches below 30°, evidence shall be provided as to suitable performance.
When fixing coverings to a pitched roof:
- the fixing schedule should be produced by the tile manufacturer; fixings for single and double lap tiles should be in accordance with BS 5534 and BS EN 1994-1-4 (evidence of calculations in compliance with Technical Requirements R3 and R5 may be required)
- coverings should be fixed in accordance with the design and the manufacturer’s recommendations
- perimeter (see definitions) roof tiles or slates should be mechanically fixed using a minimum of two fixings (subject to meeting the wind loading recommendations), one of which can be a tile clip, adhesive (following manufacturers recommendations) or dry verge capping system where designed to resist uplift
- slates and tiles should generally be fixed using clout or slate nails, these should be either silicon bronze, phosphor bronze, aluminium to BS 1202-3 or copper to BS 1202-2, additionally tiles can also be fixed using stainless steel clout nails
- galvanized steel nails should not be used for slates and tiles
- fixings should be a minimum of 38mm long, and penetrate a minimum of 15mm into battens
- tile clips should be made of aluminium alloy or other alloy types, stainless steel, non-ferrous metals or polymer based materials and be of adequate durability and strength in accordance with BS 5534
- slates should be fixed in accordance with BS 5534, fully nailed over the whole roof, and nailed twice where centre nailed. Alternatively slate hooks maybe used where they can be shown to resist wind uplift.
Where slate hooks are used they should:
- meet the requirements of BS 5534
- have a minimum shank diameter of 2.7mm
- be stainless steel grade 316 to BS EN 10088-3
- be ‘nail-in’ type slate hooks and not ‘hook-over’ batten type
- have a crimped shank when used on roof pitches less than 30 degrees. Slate hooks should not be used on roof pitches below 25 degrees.
Where the hooked fixing method is used, slates at the perimeters of a roof eg eaves, valleys, verges, ridges, hips, abutments and penetrations, should be nailed (or nailed and hooked) to resist uplift and lateral drift.
Eaves, ridge and hip tiles#
At eaves:
- tiles should project a minimum of 50mm across the gutter
- when using natural or fibre cement slates or plain tiles, an under-eaves course should be used
- the height of the facia should maintain the tile pitch, in accordance with the tile manufacturer’s recommendations.
Where ridge tiles are mortar bedded:
- on duo-pitched roofs the underlay should be lapped over the ridge in accordance with Table 10
- on mono-pitched roofs the underlay should extend over the mono ridge by a minimum 100mm
- small openings above the top batten are permitted at ridges where required for ventilation of the roof void.
At hips:
- underlay should continue to form a 150mm minimum lap parallel with the hip rafter
- where wet bedded tiles are used, they should be supported at the base by a galvanized hip iron and project to the centre line of the gutter.
Ridge and hip tiles should be mechanically fixed with self-sealing non-ferrous fixings into timber battens, and have a nominal joint thickness of 10mm where wet bedded.
Wet bedded ‘baby’ hip/ridge tiles to low level roofs, such as those over porches and ground floor bay windows, may be bedded using mortar only, subject to self-weight being sufficient to resist the wind loads, in accordance with BS 5534 (Annex H). Where no wind uplift calculation is provided, baby hip/ridge tiles should be mechanically fixed, in accordance with manufacturer’s recommendations.
Where proprietary dry fixed, ridge and hip systems are used, they should conform to BS 8612 and be installed in accordance with manufacturers requirements.
Verges#
Where proprietary dry verge systems are used, they should conform to BS 8612 and be installed in accordance with manufacturers requirements.
Unless a proprietary dry verge system or cloaked verge is used, tiles should be bedded into a 100mm wide bed of mortar on an undercloak of fibre-cement board, plain tile or slate. Undercloaks should be a minimum 150mm wide and laid face down. Plain tiles should not be used as an undercloak below 30°pitch or on a bargeboard.
Undercloak should be:
- fixed in accordance with manufacturer’s recommendations
- installed to a true line
- installed at the correct level to ensure that the line of the tiling is maintained where it passes over the wall, and not tilt inwards
- bedded on roofing mortar and struck off flush with the external surface of the wall (alternatively, a suitable exterior grade bedding sealant should be used in accordance with the manufacturer’s recommendations)
- securely nailed to a true line where a bargeboard is used.
Where verge tiles and slates are wet bedded, pointing should be completed as soon as possible using the same mix.
Verge clips should be in full contact with the tile to resist uplift, nailed twice to battens and sized to ensure that they are in direct contact with the top surface of the verge tile.
Where plain tiles and slates are used at the verge:
- they should project 38-50mm beyond the gable wall or bargeboard
- cut plain tiles are not acceptable, and purpose-made plain tile-and-a-half tiles should be used, see Figure 66
- natural slate verges should be formed with full slates and either slate-and-a-half or half slates that are a minimum of 150mm wide.
Where interlocking tiles are used at the verge:
- they should project 30-60mm beyond the gable wall or bargeboard
- small sections (less than a half tile width) of cut interlocking tiles should be avoided. Where cut tiles (less than half a tile width) are used, these should be bonded to the adjacent tile in accordance with manufacturers recommendations.
Mortar#
When bedding tiles or slates in mortar:
- the mortar should be 1:3 cement:sand with plasticiser
- the mortar should be a mix based on sharp sand with soft sand added to achieve workability; the proportion of sharp sand should not be less than one third of the total sand content (proprietary mixes may be accepted by NHBC where they are shown to have similar strength, durability and workability)
- pointing should be completed as soon as possible using the same mix
- tiles should be wetted on their contact surface, and surface water allowed to drain away before fixing
- concealed or decorative dentil tiles should be fully bedded into joints in excess of 25mm thick.
Tiling and slating to mansard roofs and dormers#
When fixing tiling and slating to mansard roofs (75° or steeper) and dormers:
- all tiles and slates should be fixed in accordance with manufacturers requirements and BS 5534
- tiles and slates should be fully nailed; single lap tiles require additional tail clips, double lap tiles (nibbed) require two nails, fibre cement slates require additional disc rivets, slates should be centre nailed
- all tiling and slating should be laid over battens and counter battens, secured to the sheathing board in line with vertical supports
- batten and counter batten sizes should be in accordance with this chapter
- a suitable breather membrane/underlay should be provided in accordance with BS 5534
- the length of the top course should ensure that the minimum headlap is maintained
- the bottom edges (eave) should be finished with an under-course tile or slate, which extends a minimum 50mm below the tilting fillet
- the eave course should be supported by a tilting fillet or other proprietary product which substantially maintains the same plane as the main cladding
- at internal or external angles, purpose-made corner tiles or soakers should be used to form weathertight joints
- where pitched roofs abuts a dormer, abutments should be formed in accordance with Clause 7.2.20 and BS 5534
- at dormer cheeks, the tiles or slates should be specified to be cut close to the slope of the roof
- where air impermeable outer weatherproof coverings eg fibre cement slates are used, ventilation behind the weatherproof covering should be in accordance with manufacturers requirements.
Vertical tiling and slating to walls should conform to Chapter 6.9 ‘Curtain walling and cladding’.
Last updated: 8th February 2024