Get the gauge wrong and the whole roof pays for it. Tiles that do not lap correctly, courses that run out at the ridge, water tracking behind the head of the tile, and a slope that fails to shed properly in driving rain. The setting out is one calculation that decides whether a pitched roof performs for decades or leaks in its first winter. It is also one of the most rushed steps on site.
This is a working guide to tile batten gauge, the standards that govern it, the safe system of work that goes with it, and the errors that keep turning up on remedial jobs.
What Batten Gauge Actually Means
Gauge is the centre to centre distance between consecutive battens. It is not the same as tile length, and it is not a fixed number for a given tile.
Gauge is derived from three things:
- The tile length or hanging length
- The minimum headlap required at the roof pitch and exposure
- The number of courses that fit between the eaves and the ridge
Single Lap Tiles
For interlocking single lap tiles, the basic relationship is:
Gauge = Tile length minus headlap
In practice the gauge is constrained by the manufacturer’s published maximum and minimum range, because the interlock controls the sidelap. A concrete interlocking tile with a 420mm length might carry a permitted gauge of 320mm to 345mm. You set out inside that window, never outside it.
Double Lap Tiles and Slates
For plain tiles and slates laid double lap:
Gauge = (Tile length minus headlap) divided by 2
A 265mm plain tile with a 65mm lap gives a 100mm gauge. BS 5534 recommends a 65mm minimum headlap for plain tiles on pitched roofs, with a maximum batten gauge of 100mm. Gauges below 88mm are not recommended, and the sidelap should be no less than one third of the tile width, typically 55mm.
Slates follow the same double lap principle, with lap driven by pitch and exposure.
The Standards Behind Roof Batten Spacing
The governing documents in the UK are:
- BS 5534:2014+A2:2018 — Slating and Tiling for Pitched Roofs and Vertical Cladding
- BS 8000-6:2023 — Workmanship on building sites, slating and tiling of roofs and claddings
- NFRC Technical Bulletin 33 — Graded Battens for Slating and Tiling
- BS 8612 — Dry fixed ridge, hip and verge systems
- HSG33 — HSE guidance, Health and Safety in Roof Work
One point worth being straight about. BS 5534 is a code of practice. Installing to it is not required by law, but its inclusion in a specification can be upheld in court, and following its guidance aids compliance with building regulations. In practice that distinction is academic. Building control, NHBC and every major warranty provider expect it, and a roof battened outside it will not pass.
Under Building Regulations, Approved Document A covers structure and Approved Document C (Site preparation and resistance to contaminants and moisture) carries requirement C2 / C4, resistance to weather and ground moisture. Wind uplift calculation sits under BS EN 1991-1-4 and BS 5534.
Getting the Batten Size Right First
Batten size depends on the covering as much as the rafter span. This is where the common site rule of thumb falls down.
Battens for single lap tiles fixed on rafters at centres up to 450mm should be 38 x 25mm. For rafter spacings up to 600mm centres they should be 50 x 25mm. Batten size for double lap tiles, on all rafter spacings, is 38mm x 25mm.
All natural slates require 50 x 25mm battens for all rafter centres. Fibre cement slates require 38 x 25mm for 450mm spans and 50 x 25mm for 600mm spans. Timber shingles and shakes need 38 x 25mm up to 450mm and 50 x 25mm for 600mm.
So a natural slate roof on 450mm centres still takes 50 x 25mm. The span alone does not tell you.
For spans greater than 600mm or other loading conditions, Annex F of BS 5534:2014+A2:2018 recommends that designs include structural calculations for strength and stiffness.
Checking Battens On Delivery
The NFRC has warned that high demand for treated timber has left an abundance of sub-standard battens in the UK market being marked, coloured and sold as BS 5534 compliant when they may be counterfeit. Colour proves nothing.
Check the thickness. BS 5534 states a batten should be 25mm thick with a tolerance of -0/+3mm, so anything under 25mm should not be used. Unequal thicknesses visible in a stack are a warning sign. Check the knots. The sum of a knot on both faces can be no more than the width of the batten, 38mm or 50mm depending on size. Dimensions are taken at a reference moisture content of 20%.
Store battens on sufficient bearers to prevent sagging or twisting.
Safety: Battens Are a Foothold, But Only Under Conditions
This matters before a single batten goes down.
The NFRC, working with the HSE, addressed this through HSG33. Graded roofing battens can be used as a foothold provided they are 50 x 25mm fixed to rafters at 600mm maximum spans, or 38 x 25mm where rafters are at 450mm maximum spans. Battens must meet the requirements of both BS 5534 and NFRC Technical Bulletin 33.
The safe system of work also requires that battens are at least 1.2m long so they span a minimum of three trusses, that they are fixed only with the recommended nails, that roofers never deliberately walk mid-span between trusses, and that they always walk on the rafter line when installing tiles and slates.
When using battens as footholds, the roofer’s weight must always be on or as close as possible to the rafter and batten junction where the fixings are, with the foot above the rafter wherever possible.
Using non-compliant battens creates a significant health and safety risk and contravenes HSG33. It may also leave the contractor stripping and re-roofing the property if the battens are proven substandard.
All of this sits alongside the Work at Height Regulations 2005 and CDM 2015 duties. Battens as a foothold are part of a system, not a substitute for edge protection or a properly planned access strategy.
Fixing Specification
Nails for fixing battens to rafters should be galvanised wire, 65mm long, with a diameter of at least 3.35mm, providing a minimum of 40mm penetration into the rafter. Compliant improved nails for nail guns should be no less than 63mm long with a diameter of 3.1mm.
Other requirements that bear directly on the work:
- Battens should be fixed to rafters at centres not more than 600mm apart unless determined by calculation, and should span at least three rafters.
- Battens must be at least 1.2m long to achieve that three rafter span.
- Nail to the centre of the rafter. Joints go directly over a rafter, square cut, tightly butted and skew nailed.
- A cut batten end should be preservative treated, with both mortar bedded and dry fix systems.
The Joint Rule Depends on Gauge
This one is regularly misquoted on site as a flat one in four.
For trussed rafter roofs where the batten gauge is more than 200mm, there should be no more than one joint in any four consecutive battens on the same rafter. Where the gauge is less than 200mm, there should be no more than three joints in any twelve consecutive battens on the same rafter.
Plain tiling at 100mm gauge falls under the second rule, not the first. Using a spread of batten lengths is a good way to meet both requirements, because it staggers the joints naturally.
Underlay Before Battens
The underlay goes on first and the battens hold it. Get the drape wrong and no amount of accurate setting out saves it.
A2:2018 introduced a maximum drape of 15mm. Drape between supports should be sufficient for free drainage, a nominal 10mm, but should not exceed 15mm in accordance with BS 5534.
Lay underlay starting at and parallel to the eaves, keeping tautness consistent. Roughly 15mm drape between rafters lets any water entering the batten cavity drain away to the gutter. Unsealed head laps should be at least 150mm over 15 degree pitch when unsupported, and 100mm when supported. Vertical side laps are a minimum of 100mm.
Underlays are classified by geographic wind zone and should only be used where the design wind pressure does not exceed the declared wind uplift resistance.
Counter Battens
If you are using a vapour permeable membrane with a close fitting roof covering such as shingles, it needs counter battening to allow ventilation of the batten space. The position of the first batten is then the batten gauge plus half the thickness of the batten.
Setting Out: The Hanging Length Method
Work from both ends inward. Never set out from the eaves alone and hope it lands.
Step One: Find the Hanging Length
Most manufacturers state the hanging length in their literature. To find it on site, turn the tile over and measure from the underside of the nib to the tail of the tile. Once established, place a tape or rule at least 50mm over the edge of the fascia board or leading edge, measured on the rake, and mark the hanging length onto the rafter. That datum point is the top edge of the eaves tile batten.
Set the first batten so the first course of tiles overhangs the gutter by 45 to 55mm, or into the centre of the gutter, whichever is the lesser distance. The overhang may need extending for wider gutters. Always check with an actual tile before moving on.
Step Two: Fix the Ridge
Leave enough room at the ridge for the top course tile, an additional tile batten, and an eaves or tops tile. The gap needed varies by manufacturer and by whether the tiles are clay or concrete.
Do not leave the ridge to be resolved at the end. That is how slopes get stripped back.
Step Three: Measure the Rake
Measure the true rafter length between those two fixed points. On the rake, not on the plan.
Measure at both verges and at the centre. Roofs are rarely square. Where the verges differ, set out to the shorter dimension and absorb the difference within tolerance.
Step Four: Divide and Check
- Divide the measured distance by the maximum permitted gauge
- Round up to a whole number of courses
- Divide the distance by that whole number to get the working gauge
- Confirm the result sits inside the permitted range
Worked example. Rafter length from top of eaves batten to top batten is 4,180mm. Tile permits 310mm to 345mm.
- 4,180 ÷ 345 = 12.11, so round up to 13 courses
- 4,180 ÷ 13 = 321.5mm
- 321.5mm sits inside the range, so the gauge is 321mm and the roof runs true
Had it landed at 355mm, add a course and recheck. Had it landed at 295mm, drop one.
Plain Tiles Need an Under-Eaves Batten
When setting out for plain tiles, the first course should be set at least 50mm over the leading edge, as with larger tiles. But an under-eaves batten must also be in place. To establish the position of both battens, check the hanging length of the standard tiles and of the eaves or tops tiles, and confirm the tails of the two align once laid.
Fixed Gauge Pantiles
For fixed gauge clay pantiles and similar products, check the recommended gauge with the manufacturer and lay a small trial area on temporary battens, or the first few courses, to confirm a good fit before battening the rest of the slope.
Marking Out on the Roof
Once the gauge is fixed, mark both verges. Use a gauge rod, a marked batten with the course positions transferred onto it, rather than running a tape cumulatively. Cumulative tape measuring accumulates error. A gauge rod does not.
Transfer the marks and chalk line across. On wide roofs, mark a third set at the centre and check the line runs true across all three. Where a hip or valley is involved, set out the main slope first and cut in afterwards. Ensure full support is provided to fix batten ends at hips and valleys.
Fix battens crown up where any bow exists, and drive nails square.
Common Roof Batten Spacing Errors
- Measuring on the plan instead of the rake. The most fundamental one. Plan dimensions are horizontal; rafter length is the hypotenuse. A 10m by 8m bungalow has an 80m² footprint, but at 40 degrees, the actual on-slope area is 104m².
- Stretching the gauge. It is bad practice, no matter how tempting, to exceed the maximum gauge, because this results in insufficient headlap, which may affect the weathering properties of the covering and void any manufacturer guarantees or warranties.
- Battening at max gauge and adjusting at the end. While technically not incorrect, this can result in poor diagonal alignment with profiled tiles, known as doglegs, and should be avoided where possible.
- Assuming both verges are equal. Measure both. On older properties and extensions the difference can be 30mm or more.
- Working to a remembered gauge. Tile ranges and fixing specifications get revised. Two visually similar tiles from the same manufacturer can carry different gauge ranges. Check the current data sheet.
- Applying the span rule to slate. Covered above. Slate takes 50 x 25mm regardless.
- Quoting the joint rule as a flat one in four. It depends on whether the gauge is above or below 200mm.
- Cumulative tape error. A 1mm error over 30 courses is 30mm at the ridge.
- Ignoring exposure when selecting headlap. Pitch alone does not fix lap. Exposure zone, altitude and topography all feed in.
For learners building their setting-out and carpentry knowledge, TradeFox offers guided trade simulations that can be repeated at their own pace. This gives learners a safe way to practise careful measurement, follow instructions, and develop more consistent working habits.
Verges, Ridges and Awkward Slopes
Under BS 8612, dry verges can no longer be installed with just a nail fixing into the end grain of the batten. Mechanical engagement must be achieved when fixing a dry verge to the batten, and a system with a batten end clip makes this easier.
All cut batten ends at the verge must be coated with a suitable timber treatment, and this applies to both mortar bedded verges and dry verge systems.
Where a roof has a change of pitch, a mansard or a dormer, set out each plane independently. Do not carry a gauge through a pitch change. Where courses must align across a dormer cheek, set out the main slope first and adjust the dormer to suit.
On low pitch roofs approaching the tile’s minimum permitted pitch, tolerance evaporates. Lap increases, gauge tightens, and there is no room to absorb an error.
Recording and Verifying
The fixing specification should be site-specific and documented: tile, pitch, exposure, gauge, headlap, sidelap, batten size, nail specification and fixing pattern. That is what building control or the warranty provider will ask to see.
Wind uplift calculations to BS EN 1991-1-4 and BS 5534 are complex to undertake, and designers are advised to obtain a full roofing fixing specification. Use the manufacturer’s specification tool rather than working it up from scratch.
Photograph the battened slope before the tiles go on, with a tape in shot showing the gauge. Two minutes, and it is the only evidence that exists once the roof is covered.
