Summary

Batten spacing is one of the few jobs on a pitched roof where getting it wrong is invisible until the first heavy rain — but it is the single biggest determinant of whether the roof keeps water out. Every tile manufacturer publishes a minimum headlap table indexed against pitch, and the batten gauge is derived from that. Roofers who set gauges from memory rather than the published tables end up either over-gauging (water ingress at low pitch) or under-gauging (wasted tiles and cut courses at the eaves).

BS 5534 was substantially revised in 2014 (and amended again in 2018) after several years of wind-uplift failures. The standard now treats batten spacing, fixing pattern, and underlay as a single integrated system. You cannot mix-and-match a manufacturer's lap with a non-compliant fixing pattern and expect the roof to perform.

The other common misconception is that "the steeper the roof, the safer you are." That is true for water shedding but not for wind uplift — steep roofs catch more wind. The headlap minimums in BS 5534 reflect water performance only; mechanical fixing requirements (BS 5534 Annex A wind calculation) are a separate calculation and apply at all pitches.

Key Facts

Standards and definitions

Headlap by tile family

Batten requirements

Quick Reference Table

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Tile type Min pitch Headlap at min pitch Gauge (approx)
Plain clay/concrete tile (265 mm) 35° 65 mm 100 mm
Plain tile at 40°+ 40° 65 mm 100 mm
Plain tile at 35° 35° 75 mm 95 mm
Marley Modern (interlocking) 17.5° 100 mm 338 mm
Marley Modern at 22.5°+ 22.5° 75 mm 343 mm
Redland Cambrian slate 17.5° 100 mm 300 mm
Sandtoft Double Roman 22.5° 75 mm 343 mm
Clay pantile 30° 75 mm 260 mm
Natural slate 500×250 25° 90 mm 205 mm
Natural slate 600×300 22.5° 100 mm 250 mm
Fibre cement slate 600×300 20° 100 mm 250 mm

Always verify exact gauge against the specific manufacturer's fixing instructions — the values above are typical, not authoritative.

Detailed Guidance

Calculating gauge from pitch

Single-lap (interlocking) tile gauge:

gauge = tile_length - headlap

For example, a Marley Modern is 420 mm long. At 22.5° pitch with 75 mm headlap, gauge = 420 − 75 = 345 mm.

Plain (double-lap) tile gauge:

gauge = (tile_length - headlap) / 2

For a 265 mm plain tile at 40° with 65 mm headlap, gauge = (265 − 65) / 2 = 100 mm.

Setting out from eaves to ridge

Measure the rafter length from the top of the fascia (or top of tilting fillet) to the top of the ridge board. Subtract the eaves overhang (the distance the first batten sits forward of the wall plate — typically 38–50 mm so the first course oversails the gutter) and the ridge tile bedding margin (typically 60–80 mm, check the ridge tile spec).

Divide the remaining length by the maximum gauge from the manufacturer's table. Round up to the next whole number of courses. Recalculate the actual gauge: actual = (length / courses), rounded down. This will always be equal to or less than the maximum gauge, so headlap is preserved or increased — never less.

Worked example — Marley Modern at 30° pitch

The first batten goes at the eaves position, the next at 340 mm above it, and so on for 12 spacings. The top batten then sits within the ridge bedding margin.

Pitch bands and the BS 5534 minimums

Headlap requirements step up as pitch drops, in roughly these bands:

Pitch          | Headlap multiplier
60°+           | manufacturer minimum (typically 65-75 mm)
45-60°         | manufacturer minimum
30-45°         | manufacturer minimum
22.5-30°       | +10-15 mm above minimum
17.5-22.5°     | +25 mm above minimum
Below 17.5°    | NOT PERMITTED for most tiles

Some interlocking tiles (e.g. Redland Cambrian) are certified down to 15° but require specific underlay specifications and continuous support battens.

Exposure and the wind zone factor

BS 5534 splits Great Britain into wind speed zones. The Annex A wind uplift calculation determines whether tiles need every-course mechanical fixing, perimeter-only fixing, or every-other-course fixing. Sites above 100 m altitude, within 5 km of the coast, or on exposed hilltops generally require every-course fixing regardless of tile weight. Since 2015 every roof in the UK has had to comply with this — the old "fix every fifth course" rule of thumb is non-compliant.

Counter-battens and ventilation

On warm roofs and on roofs with breathable underlay where the manufacturer requires a drained and ventilated air space, 25 × 50 mm counter-battens are fixed up the line of each rafter before the cross battens go on. This adds 25 mm to the eaves overhang calculation. Counter-battens are mandatory under BS 5250 for some warm roof build-ups.

Common mistakes

Frequently Asked Questions

Can I use a tile below its minimum certified pitch?

No. The pitch limits in the manufacturer's BBA certificate or fixing instructions are the binding minimum. Going below them voids the certification, the warranty, and the building control sign-off. If you have a 12° pitch, you need a fully-supported metal roof, GRP, single-ply membrane, or a tile system certified to that pitch (rare).

What if my rafter length doesn't divide neatly by the maximum gauge?

That is the normal case. The setting-out procedure handles it: divide, round courses up, recalculate gauge down. The actual gauge is always slightly less than the maximum, giving a slightly larger headlap. Never round courses down — that gives less headlap than the minimum and is a code violation.

Are pressed steel battens or aluminium battens allowed under BS 5534?

Yes, where they carry independent third-party certification (BBA or equivalent) showing equivalent or better performance than BS 5534 graded timber battens. Steel battens are common on commercial and high-rise jobs but rarely seen on domestic work. They cost 3-4× the price of timber.

How do I gauge a roof when the rafter length is different on each side?

Each pitch is calculated separately. The ridge tiles span both pitches and accommodate small differences. If the differences are large (>50 mm), recheck the carpentry — rafters should have been cut to equal length unless the spans differ.

Does the underlay affect batten spacing?

Not directly, but breathable underlays require a 25 mm minimum unobstructed drainage gap above the felt. If you're laying counter-battens to create that gap, they must be tall enough (25 mm) and the cross battens above them must still meet the BS 5534 spacing rules. The underlay manufacturer's instructions may also require additional batten support at laps.

Regulations & Standards