Choosing between tiles and slates is rarely just an aesthetic call. Coverage rates, weight, fixing schedules and ventilation strategy all interact — get one wrong and you’ll be back on the roof within a decade. This guide works through each factor using the figures roofing contractors and building inspectors actually use.
Tiles and Slates Per m² by Type
Coverage is driven by the minimum headlap — the amount of each unit hidden beneath the one above — which in turn depends on roof pitch and exposure zone. The table below shows typical ranges for the main product families at a 35° pitch in a sheltered location; reduce headlap (and raise coverage) only with manufacturer approval and within BS 5534 limits.
| Product type | Units/m² (approx.) | Weight (kg/m²) | Min pitch | Typical batten gauge (mm) |
|---|---|---|---|---|
| Concrete interlocking plain tile | 9–12 | 40–50 | 17.5° | 90–100 |
| Concrete double-roman / pantile | 9–11 | 40–45 | 12.5° | 300–345 |
| Clay plain tile (267 × 165 mm) | 60–65 | 65–70 | 35° | 90–100 |
| Clay single-camber machine-made | 14–16 | 30–40 | 15° | 280–340 |
| Natural Welsh slate (600 × 300 mm) | 16–18 | 30–35 | 25° | 255–275 |
| Natural Spanish slate (500 × 250 mm) | 22–28 | 25–30 | 20° | 185–215 |
| Fibre-cement slate (600 × 300 mm) | 16–18 | 14–18 | 20° | 255–275 |
| Reconstituted stone slate | 14–22 | 45–70 | 22.5° | Varies |
Gauge = (exposed length) = (slate/tile length − headlap) ÷ 2 for slates; for single-lap tiles it equals the full exposed height. Always take batten gauge from the manufacturer’s technical data sheet verified against BS 5534 Section 6.
Nailing and Clipping: BS 5534 Requirements
BS 5534:2014+A2:2018 (Slating and tiling for pitched roofs and vertical cladding) is the current governing standard. The headline change since the 2014 revision — reinforced in the 2018 amendment — is that every tile or slate must be mechanically fixed unless a wind uplift calculation demonstrates otherwise. In practice that means:
For tiles: either a nail through the nibs plus a clip, or a purpose-made interlocking clip system. Head-nailing alone is acceptable only where uplift loads are demonstrably low. The standard distinguishes between course-nail-and-clip (every tile) and tail-nail (plain tiles nailed at the tail rather than the head) depending on product geometry.
For slates: two copper, aluminium or stainless-steel nails per slate, minimum 3.35 mm diameter, driven into 38 × 25 mm (min.) treated softwood battens. Single-nail fixing is not compliant except on purpose-designed single-nail slates with proprietary clips.
Nail penetration into the batten must be at least 25 mm; through-fix into rafter is required where battens cannot provide adequate embedment.
BS 5534 Annex A provides wind uplift calculation methodology by exposure zone (mapped against BS EN 1991-1-4 UK National Annex). Most of coastal Wales, Scotland, Northern Ireland and exposed upland England fall into Zone D/E where additional mechanical fixing (clips at every course) is mandatory.
Practical costs for fixings per 100 m² roof:
- Annular-ring shank nails (stainless, 3.35 mm × 30 mm, 1,500-pack): £25–£40
- Aluminium or stainless tile clips (bag of 250): £18–£30
- Copper nails for natural slate (1 kg, approx. 500 nails): £12–£20
Dry Verge and Dry Ridge Systems
Traditional mortar at verges and ridges is now considered a liability: cement joints crack within 10–15 years, admit water, and can dislodge without warning. Dry-fix systems, mandated on new-build by many warranty providers (NHBC Technical Standards, Chapter 7.2) and strongly recommended on replacement work, eliminate mortar entirely.
Dry verge: Plastic (uPVC or polypropylene) capping units click onto a continuous under-tile support tray fixed to a barge board or fascia. They interlock along the slope to prevent wind-driven rain ingress. Avoid purely push-fit systems in severe exposure; specify mechanically fixed units with stainless screws. Material cost: £4–£8 per linear metre.
Dry ridge: A flexible roll underlay bedded onto the ridge tiles, held by a continuous aluminium or uPVC ridge carrier and stainless screws into the ridge board. Each ridge tile is individually secured. The carrier also provides 5–10 mm equivalent ventilation opening, satisfying Part L requirements when used as part of a ventilated cold roof. Material cost including carrier, clips and roll: £12–£20 per linear metre.
Eaves and Ridge Ventilation
Building Regulations Approved Document C and Part L both reference BS 5250:2021 (Management of moisture in buildings) on ventilation requirements. For a cold pitched roof (insulation at ceiling level):
- Eaves: minimum 25 mm continuous free air path, typically provided by over-fascia vents or ventilated soffit panels. The “50 mm eaves ventilation” commonly specified means 25 mm equivalent open area across the roof width.
- Ridge: corresponding outlet is required at or near the ridge — minimum 5 mm continuous equivalent open area per pitch. Dry ridge systems, high-level tile vents at 1–1.5 m spacing, or a purpose-made ridge vent tile all satisfy this.
- Counter-batten air path: where a breather membrane sits directly on rafters, 38 mm counter-battens above the membrane maintain the 25 mm cross-ventilated air space.
For warm roofs (insulation between and/or above rafters), ventilation to the roof void is not required but vapour control on the warm side of the insulation becomes essential.
Ventilation tile or vent unit rates: clay or concrete in-line vent tiles £8–£18 each; over-fascia vent strips (1.2 m length) £4–£8; high-level tile vents (150 × 150 mm equivalent area) £12–£25 each.
Material Cost Summary
| Material | Supply cost (£/m², 2026) | Notes |
|---|---|---|
| Concrete interlocking tiles | £8–£16 | Budget to mid-range; includes clips |
| Clay plain tiles | £22–£45 | Handmade clay at top end |
| Natural Welsh slate | £30–£60 | Source and grade dependent |
| Natural Spanish/Portuguese slate | £18–£35 | S1 grade preferred for UK exposure |
| Fibre-cement slate | £10–£18 | 40-year BBA-certified products |
| Reconstituted stone slate | £25–£55 | Region-specific aesthetics |
These are material-only supply costs; add roofing labour at £18–£28/m² for tile work and £22–£35/m² for natural slate on typical domestic projects. Scaffolding and associated costs are additional.
Relevant Standards and Guidance
- BS 5534:2014+A2:2018 — primary standard for all slating and tiling
- BS 8612:2018 — dry-fixed ridge, hip and verge systems
- BS 5250:2021 — moisture management including roof ventilation
- NHBC Standards Chapter 7.2 — pitched roofs (warranties require BS 5534 compliance)
- Approved Document C — site preparation and resistance to moisture
- Approved Document L (2021 edition) — conservation of fuel and power, thermal performance
When specifying any roofing system, the wind uplift calculation to BS 5534 Annex A should be carried out or confirmed by the roofing contractor and retained as part of the building file — increasingly expected by building control bodies and warranty inspectors.
