Roofing Battens: Sizes, Spacing, BS 5534 Compliance and What to Check on Site

Your roofer turns up with a stack of battens that look right. They're blue-tinted, roughly the right size, and they're going on the roof before you've had your morning coffee. Six months later, building control flags a problem: the battens aren't BS 5534 graded. The tile manufacturer's warranty is void. Your insurance won't cover a claim. And the only fix is to strip the entire roof, buy compliant battens, and start again. That scenario plays out more often than it should, and it's entirely preventable if you know what to look for when the battens arrive on site.

What they are and what they're for

Roofing battens are horizontal strips of treated softwood nailed across the rafters of a pitched roof. Tiles hang from them. Every tile on a pitched roof hooks over a batten via a small projection on the back of the tile called a nib. Without battens, there's nothing to hold your tiles in place.

They look like simple strips of wood, and in one sense they are. But they're structural. They carry the full dead load of the tiles (which can be 40 to 60 kg per square metre for concrete), plus snow loading, plus wind uplift forces that try to rip tiles off the roof. A batten that snaps underfoot during installation is a fall hazard. A batten that rots because it wasn't properly treated will sag under the tile weight within a few years, opening gaps for water to get in.

The governing standard is BS 5534:2014+A2:2018 (the UK code of practice for slating and tiling). It specifies that roofing battens must be machine-graded, preservative-treated to Use Class 2 under BS 8417, and indelibly stamped with the manufacturer's name, timber species code, "BS 5534," and the batten size. On-site grading is not permitted. You can't rip a larger piece of timber down to size and call it a roofing batten.

Types, sizes, and specifications

There are two standard sizes and the right one depends on your rafter spacing and tile type.

The 25mm dimension is the thickness (depth). It must never be less than 25mm, with a manufacturing tolerance of minus zero, plus 3mm. If you measure a delivered batten and it's 24mm thick, reject it.

The width (38mm or 50mm) determines how much bearing area the tile has and how much nail pull-out resistance the batten provides. At 600mm rafter centres (the standard for most trussed roofs), 38mm-wide battens don't have enough span strength. The batten flexes, tiles shift, and nail fixings loosen. That's why 50mm width is mandatory above 450mm centres.

There's one exception that catches people: natural slate. Even at 450mm rafter centres, slate requires 50mm-wide battens because the individual slates are heavier per fixing point than interlocking tiles.

And if anyone on your site needs to walk on the battens during installation (they will), only 50 x 25mm battens on rafters at 600mm centres or less qualify as safe footholds under HSE guidance. That's not optional. It's a safety requirement backed by NFRC Technical Bulletin 33.

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Treatment and marking

Every roofing batten must be pressure-treated with preservative to Use Class 2 (the standard for timber in persistent risk of wetting but not in ground contact). The treatment penetrates deep into the timber under vacuum and pressure. You can't replicate this at home with a tin of Cuprinol.

The colour of the treatment (commonly blue, red, or orange) tells you nothing reliable. Counterfeit battens have become a documented problem in the UK market. LABC, NFRC, and all major tile manufacturers have issued warnings. Some non-compliant products are deliberately coloured to look like treated, graded battens.

What you need to see on every batten is four indelible markings:

1. Manufacturer name
2. Timber species code (WPCA for spruce, PNSY for pine)
3. "BS 5534" (this confirms grading, not just treatment)
4. Size (e.g. 25 x 50)

What happens with non-compliant battens

The consequences stack up quickly. NHBC and LABC inspectors will reject battens that don't carry the BS 5534 mark. Tile manufacturers (Marley, Redland, Sandtoft) void their product warranties if tiles are installed on non-graded battens. Your building control sign-off is at risk. And because battens sit under every tile on your roof, the only remedy is a complete strip and re-batten, with all the scaffolding, labour, and tile-handling risk that entails.

Forum threads are littered with homeowners who discovered too late that their roofer used cheap, ungraded battens. The cost of replacement dwarfs the saving. Battens are one of the cheapest materials on any roof. Cutting corners here to save a trivial amount is reckless.

How to work with them

Calculating the gauge

The gauge is the centre-to-centre spacing between battens, and it's dictated by the tile. Every tile type has a maximum gauge (the largest spacing that still provides enough overlap to keep water out) and that figure comes from the tile manufacturer's data sheet.

The method is straightforward. Measure the tile's hanging length: from the underside of the nib (the hook that sits over the batten) to the bottom edge of the tile. Subtract the headlap (the amount the upper tile overlaps the lower one, typically 75mm or 100mm). The result is your maximum gauge.

A worked example: Marley Modern tiles with 75mm headlap have a maximum gauge of 345mm. At 100mm headlap, it drops to 320mm.

To set out battens on the roof, you work from both ends. The eaves batten position is set first (the tile must overhang the fascia by 45 to 55mm to direct water into the gutter). The top batten position is set so that ridge tiles overlap by at least 75mm. Then you divide the distance between the two into equal courses at or below the maximum gauge.

Fixing battens to rafters

Each batten is nailed to every rafter it crosses with a single 65mm x 3.35mm galvanised round wire nail, driven straight through the batten into the rafter. The nail must penetrate the rafter by at least 40mm. Nail-gun equivalents (63mm x 3.1mm minimum, ring-shank, galvanised) are also acceptable under BS 5534.

Battens must span at least three rafters. The minimum individual batten length is 1.2 metres. Joints must fall directly over a rafter, and for gauges above 200mm, no more than one in four battens should be jointed over the same rafter. Skew-nail each joint end to prevent the batten lifting.

Battens cannot be re-sawn or planed after treatment. Cutting to length is fine, but any cut ends that will be exposed at a verge (the edge of the roof at a gable) must be treated with end-grain preservative before tiling.

Installation sequence

The breathable roof membrane goes on first, draped over the rafters with 100mm horizontal laps (150mm at vertical end laps) and secured with counter battens or temporary fixings. Battens are then fixed on top of the membrane.

Start with the eaves batten. Position it so a sample tile overhangs the fascia by 50mm (or to the centre of the gutter, whichever is less). The eaves batten sits slightly higher than subsequent battens because of the tilting fillet or raised fascia detail that kicks the first course up to match the angle of the courses above.

Work upward to the ridge. The top batten position must allow ridge tiles to overlap the top course by at least 75mm. If you're using a dry ridge system, the ridge batten and batten straps go on before the ridge components.

Storage on site

Battens arrive in bundles and they warp quickly if stored badly. Lay them flat on bearers (timber blocks or bricks) to keep them off the ground and prevent sagging. Cover them to protect from rain. Battens saturated with water will shrink as they dry after installation, causing tile movement and gaps. BS 5534 requires moisture content at installation to be 22% or below.

Don't leave them standing upright against a wall. Don't leave them in a stack on wet ground. If you're taking delivery days before the roofer starts, store them in a garage or under a proper tarpaulin, not just a sheet of polythene that will pool water on top of the stack.

How much do you need

The calculation is simple once you know the gauge.

Step 1: Measure the rafter length (the sloped distance from eaves to ridge, in metres).

Step 2: Divide by the gauge (in metres). For 345mm gauge: rafter length / 0.345. Round up to a whole number and add 1 for the eaves batten.

Step 3: Multiply the number of rows by the roof length (the horizontal distance along the ridge, in metres). If you have two roof slopes, multiply by 2.

Step 4: Add 10% for waste (joints, cutting, and damaged battens).

Worked example for a 5m x 4m rear extension with a pitched roof at 35 degrees, using interlocking tiles at 345mm gauge:

• Rafter length: approximately 4.9m (4m horizontal span corrected for pitch)
• Batten rows: 4.9 / 0.345 = 14.2, round up to 15, plus 1 eaves batten = 16 rows
• Roof length: 5m, two slopes: 5 x 2 = 10m
• Total batten: 16 x 10 = 160 linear metres
• Plus 10% waste: 176 linear metres
• In 4.8m lengths: 176 / 4.8 = 36.7, round up to 37 lengths. Add 10% for offcuts and joints: 41 lengths.

That's a small fraction of your total roof cost, as the pricing section below shows.

Cost and where to buy

Roofing battens are cheap. The material cost for an entire extension roof is typically under two hundred pounds at trade prices. But the price varies depending on where you buy.

Specialist roofing suppliers (JJ Roofing Supplies, Roofing Superstore, Burton Roofing) are the cheapest source and the most reliable for BS 5534 compliance. Trade pricing from these suppliers sits in the lower half of the ranges above, and bulk orders above 600 metres bring it down further.

Builders' merchants (Travis Perkins, Jewson) carry roofing battens but pricing is inconsistent and you'll need a trade account for the best rates. Expect prices somewhere between specialist and retail depending on the branch and your account terms.

The DIY retail end of the market charges a premium. Wickes, for example, sells battens in packs of 8 x 3.6m at close to the top of the retail range shown above. That's nearly double the specialist price per metre. If your roofer is buying from Wickes, they're not buying many roofs.

Standard lengths are 3.6m and 4.8m. Longer lengths (5.1m, 5.4m) are available from some suppliers at a surcharge but aren't necessary for typical extension work.

Checking what arrives on site

This is what separates an informed homeowner from one who finds out too late. When battens are delivered, check five things:

The stamp. Every batten should have an indelible mark reading "BS 5534" along with the manufacturer name, species code, and size. Not just "BS 8417" (that's treatment only). Not just a colour tint. The actual words "BS 5534" stamped into the timber.

Documentation. Ask for the delivery note. It should state the supplier, origin, grade, size, and treatment type. NHBC inspectors will ask for this. Have it ready.

Thickness. Bring a tape measure. Spot-check five or six battens. The thickness must be 25mm minimum (tolerance is minus zero, plus 3mm). If any batten measures under 25mm, reject the delivery.

Visible defects. Look for rot, splits, insect damage, excessive knots, and resin pockets. A knot that runs across more than half the width of the batten weakens it. Wane (where the curved outer edge of the original log shows as bark or missing wood on the corner of the batten) reduces the bearing surface for nails.

Moisture. Battens should feel dry to the touch, not saturated. If they've been left out in the rain, they may be above the 22% moisture content limit. A moisture meter gives you the exact reading. Cheap pin-type meters cost around fifteen pounds from any tool supplier and take ten seconds to use.

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Alternatives

There aren't direct alternatives to roofing battens on a pitched tiled roof. If you have tiles, you have battens. The only decisions are size (covered above) and whether you also need counter battens.

Counter battens are vertical strips (typically the same cross-section as the roofing battens) fixed to the rafters before the horizontal tiling battens go on top. They create a ventilation channel between the membrane and the tiles. Standard concrete and clay tile roofs with a breathable membrane typically don't need counter battens. But if the roof has close-fitting coverings (timber shingles, for example) or if the tile manufacturer specifies them, they're required. Your roofer and the tile data sheet will confirm whether your roof needs them.

For flat roofs, battens aren't used at all. EPDM rubber membrane and GRP fibreglass systems use a different substrate entirely (typically timber decking boards).

Common mistakes

Wrong size for the rafter spacing. Using 38 x 25mm battens on 600mm rafter centres because they're cheaper. They'll sag, the nail fixings will weaken, and the tile warranty is void. Forum threads document roofers doing exactly this and homeowners having to insist on replacement.

Relying on colour to confirm compliance. The blue tint means the timber has been through a treatment process. It doesn't mean it's been graded. Counterfeit battens are a real problem. Check the stamp.

Stretching the gauge. Setting battens slightly further apart than the tile manufacturer's maximum to save a row of battens. The headlap reduces, water ingress risk increases, and building control will catch it with a tape measure.

Not treating cut ends. Every batten cut to length at a verge has an untreated end face exposed to weather. A brush application of end-grain preservative takes ten seconds and prevents rot starting at the most vulnerable point.

Storing battens flat on wet ground. Timber soaks up ground moisture and swells. After installation it shrinks, tiles move, gaps open. Bearers and a tarpaulin cost nothing.

DIY battens from ripped-down timber. Cutting your own from larger stock seems like a saving, but you can't replicate pressure treatment at home, you have no way of grading for knot defects, and building control won't accept them. The cost difference is negligible anyway.

Where you'll need this

• Roof covering - battens are fixed at gauge spacing to support tiles, laid after the breathable membrane and before any tiles go on

Roofing battens appear during the structure phase of any extension or renovation project that includes a pitched roof. They're installed once the roof structure (rafters, ridge board) is complete and the breathable membrane is in place, and they must be finished before tiling can begin.