Pitched Roofing Guide: Tiles, Slates, Underlay, Battens and Specification Rules

Quick Answer: UK pitched roofs are governed by BS 5534:2014+A2:2018 (slating and tiling code of practice) and Building Regulations Part L (thermal) and Part C (moisture). Tile selection, batten size, fixing pattern and underlay all depend on roof pitch, exposure zone and tile/slate type. Minimum pitches range from 12.5° (low-pitch interlocking concrete tiles) to 35° (plain clay tiles); battens must be minimum 38 × 25 mm BS 5534-graded; nails must be 3.35 mm diameter copper or stainless. Get pitch and exposure right at quote stage — the wrong tile on the wrong pitch will leak before the final invoice clears.

Summary

Pitched roofing is the dominant UK roof form — over 80% of housing stock has a duo-pitch roof finished in concrete tiles, clay tiles or slates. The trade has been formalised heavily since the 2014 revision of BS 5534, which tightened fixing patterns, banned the use of mortar bedding alone for verges and ridges, and mandated mechanical fixings for ridge and hip tiles. Knowing the rules matters because Building Control inspectors and NHBC technical have both started enforcing them on routine work.

The job sits on five technical pillars: pitch (the angle the rafters create), tile choice (mass, profile, headlap), batten size and grade, underlay type and breathability, and the fixing schedule (how many tiles get nailed and clipped, calculated from BS 5534 Table 2 for the building's exposure zone). Get any one wrong and the roof leaks, lifts or fails Building Control.

A pitched-roof contractor pricing a re-roof needs to think about all five at quote stage. Substituting a "similar" tile that turns out to need a higher minimum pitch is the most common single quote-stage error. Specifying a non-breathable underlay over an unventilated cold roof is the second.

Key Facts

• BS 5534:2014+A2:2018 — code of practice for slating and tiling, the authoritative document
• Standard batten size — 38 × 25 mm (small tiles, slates), 50 × 25 mm (heavy tiles, large spans)
• Batten grade — must be BS 5534 graded, marked with a yellow/red end stripe
• Nail spec — 3.35 mm shank diameter minimum, copper or austenitic stainless steel
• Standard headlap (interlocking concrete tile) — 75 mm typical, can be 100 mm in higher exposure
• Plain tile (clay) — minimum 35° pitch, 65 mm headlap, double-lap construction
• Slate (natural) — minimum 25° pitch on standard slates, 100 mm headlap typical
• Underlay (Type LR, breathable) — replaces 1F bituminous on most modern roofs, allows vapour to escape
• Underlay (Type 1F bitumen) — only acceptable with continuous high-level ventilation
• Tile clip spec — every tile in single-storey buildings, edge tiles + every 5th tile in lower zones for two-storey
• Mortar bedding — only acceptable as an aesthetic finish; mechanical fixing required for hip, ridge and verge under BS 5534
• Dry-fix systems — clipped, screwed and gasketed; eliminate mortar at ridge, hip, verge
• Eaves overhang — 50 mm minimum into gutter, 75 mm typical
• Valley — 175 mm minimum lead width to each side of centre, or proprietary GRP/aluminium valley trough
• Ridge tile fixing — every ridge tile mechanically fixed (BS 5534 mandatory since 2014)
• Wind exposure zones — 1 (sheltered) to 5 (severe coastal/upland), determined by BRE Digest 346 and post code lookup
• Ventilation — at eaves and ridge, sized per BS 5250: 25 mm continuous opening at eaves + 5 mm at ridge typical for cold pitched roof

Quick Reference Table

Detailed Guidance

Setting the Pitch

The pitch is fixed by the rafters and determines what tile or slate is allowable. Below 22.5°, the only domestic options are low-pitch interlocking concrete tiles or modern profiled metal sheet (standing seam aluminium or zinc). Below 15°, the roof is effectively flat and falls under flat roofing rules (flat roof falls and drainage applies).

Critical pitches by tile family:

• 12.5° — minimum for "low-pitch" interlocking concrete tiles (specific products only, e.g. Marley Mendip Lo, Redland Cambrian)
• 17.5° — minimum for some interlocking clay tiles
• 22.5° — standard interlocking concrete and clay
• 25° — natural slate (and most cement fibre slates)
• 30° — pantiles, double Roman
• 35° — plain tiles (clay and concrete)

Picking a tile below its minimum is a guaranteed leak. The published minimum is the minimum at which the tile's headlap can drain water under wind-driven rain. Below it, the water simply runs uphill at the laps.

Battens: The Forgotten Spec

Battens hold the tiles. They must be:

• Strength-graded to BS 5534 — marked with a yellow or red stripe at the end. Untreated, ungraded battens are not acceptable on any roof since 2014.
• Section size — 38 × 25 mm minimum for small tiles (slate, plain), 50 × 25 mm for larger tiles or where rafter centres exceed 600 mm
• Treatment — preservative-treated to BS 8417 Use Class 2
• Joints — staggered, never on the same rafter as adjacent battens, supported on rafters at both ends
• Fixing — 65 mm minimum into rafter, with stainless or galvanised nails

Underlays: The Vapour Question

Underlay is the secondary barrier between tile and structure. The two families:

• Type 1F bitumen felt — non-breathable, cheap, traditional. Only acceptable on roofs with continuous high-level (ridge) and low-level (eaves) ventilation. Functions purely as a water shedder and wind layer.
• Type LR breathable membrane — synthetic non-woven, water-resistant from above, vapour-open from below. Used in unventilated and partially ventilated cold-roof and warm-roof builds. The default on most new builds and re-roofs.

The choice interacts with insulation position:

• Cold roof (insulation at ceiling level) — needs underlay AND eaves/ridge ventilation, regardless of underlay type
• Warm roof (insulation at rafter level) — usually paired with breathable underlay; vapour control layer (VCL) on warm side of insulation
• Hybrid — both — vapour control critical, mistakes here cause condensation between layers (interstitial condensation in modern roofs)

Fixing Patterns and Wind Zones

BS 5534 categorises UK postcodes into wind exposure zones 1 (sheltered) to 5 (severe). Each zone has a tile-by-tile fixing schedule:

• Zone 1–2 (low-rise inland) — perimeter tiles all fixed; field tiles every fifth tile clipped (interlocking) or every tile nailed (slate, plain)
• Zone 3 (most of the UK) — perimeter all fixed; field tiles minimum every third clipped/nailed
• Zone 4–5 (coastal, upland) — every tile clipped/nailed

Roof type matters too. Two-storey houses get standard fixing schedules; bungalows and tall single-storey get enhanced fixings. Buildings over 18 m height get a SE-designed fixing pattern.

Hip, Ridge, Verge: The Dry-Fix Era

Since 2014, all ridge, hip and verge tiles must be mechanically fixed (clipped or screwed) in addition to any mortar finish. Pure mortar bedding is not allowed. The compliant options:

• Dry-ridge system — proprietary roll, batten and clip system; ridge tiles screwed to a continuous batten through gasket strips. No mortar.
• Dry-verge system — preformed plastic or aluminium verge trim, clipped to tile edges
• Dry-hip system — galvanised hip iron or proprietary hip tray with mechanical fixings
• Mortar + clip hybrid — mortar bedding for aesthetic, with concealed clips behind. Acceptable on heritage where dry-fix is visually inappropriate.

Local Authority Building Control will increasingly reject roofs without dry-fix or hybrid mechanical fixing on inspection.

Valleys, Soakers, Step Flashings

Valleys are the most failure-prone detail on a pitched roof. Three options:

• Lead-lined valley — Code 5 minimum, 175 mm lead each side of centre, in 1.5 m maximum lengths to allow for thermal movement (see leadwork specification)
• GRP valley trough — preformed in 3 m lengths with lapped joints; cheaper than lead, simpler to fit
• Cut-mitre valley (close-cut) — interlocking tiles cut at angle, no trough; only acceptable on specific tile types and pitches

Soakers (lead pieces interlocking with each course of slate or tile against an abutment) are mandatory under BS 5534 wherever a roof meets a wall or chimney.

Cold vs Warm Roof Construction

A pitched roof can be insulated at three levels:

• Cold roof — insulation between/over ceiling joists. Loft is uninsulated and vented. Cheap, traditional, common on existing housing.
• Warm roof — insulation between/over rafters. Loft becomes habitable (or potentially habitable). VCL critical.
• Hybrid — partial insulation at ceiling + at rafter line. Risk of condensation in the void between if VCL is wrong.

For loft conversions, a warm-roof build is mandatory (loft conversion insulation rules cover U-value targets and detailing).

Frequently Asked Questions

Can I lay slate on a 22° pitch?

Standard slate sizes (400×200 mm) are designed for 25° minimum. At 22° you'd need to either increase the headlap to 130 mm and accept the cost in slate count, or use a specifically engineered low-pitch slate system. Don't simply lay standard slate at 22° — the manufacturer warranty won't cover it.

Are interlocking concrete tiles still acceptable on heritage work?

Aesthetically, no — most conservation areas and listed buildings require natural slate, plain clay tile or stone slate matching the original. Practically, modern smooth-finish "thin-leading-edge" concrete tiles can sometimes be approved on lesser-grade conservation work. Always check with the local Conservation Officer before quoting.

Why are some battens stamped red and others yellow?

The stripe colour indicates the strength grade — yellow is BS 5534 medium duty, red is BS 5534 high duty. Both are acceptable but high-duty battens are required where rafter centres exceed 600 mm or for heavy tiles.

What's the cheapest compliant re-roof?

Concrete interlocking tiles on Type LR breathable membrane with 38 × 25 mm graded battens, clipped per zone 3 fixing schedule, dry-ridge and dry-verge. Around £85–£120/m² fitted on a straightforward two-storey terrace, including strip-off and skip.

Do I need scaffold for a re-roof?

Yes — Working at Height Regulations 2005 require collective fall protection (scaffold or fall arrest system) for any work above 2 m. Mobile towers and ladders alone are not adequate. Roof access is the single biggest cost on small re-roof jobs. See roof safety, edge protection and scaffold for the WAH compliance rules.

Regulations & Standards

• BS 5534:2014+A2:2018 — slating and tiling code of practice (the document)

• BS 8000-6 — workmanship on building sites — slating and tiling

• BS 8417 — preservation of timber — for batten treatment

• Building Regulations Part L (2021) — thermal performance, U-value targets

• Building Regulations Part C — moisture resistance, ventilation paths

• BS 5250 — code of practice for control of condensation in buildings

• BRE Digest 346 — wind exposure zones and tile fixing

• NHBC Standards Part 7 — current technical guidance on roof construction

• BS 8000-4 — structural ironwork including verge and ridge fixings

• BS 5534 Slating and Tiling — British Standards Institution

• NFRC Technical Bulletins — National Federation of Roofing Contractors

• NHBC Standards Chapter 7 — current pitched roof technical guidance

• Marley / Redland Technical Manuals — manufacturer fixing specifications

• LABC Technical Guidance — local authority Building Control practitioner notes

• Approved Document L (2021) — current U-value requirements

• tile types and selection guide — detailed comparison of UK tile families

• pitched roof structural elements — rafters, purlins and trusses

• re-roofing scope and strip-off — when to recover vs replace

• leadwork on pitched roofs — flashings, valleys, soakers

• roof safety and edge protection — WAH-compliant access for re-roof work