Roof battens are the horizontal softwood members fixed across the rafters to which tiles or slates are nailed. They look simple but are precisely specified items: the wrong size, grade or spacing can lead to structural failure under wind uplift, premature decay, or tiles slipping out of gauge. Since the 2014 revision of BS 5534, grading requirements have become mandatory rather than advisory.
BS 5534 Grading Requirements
BS 5534:2014 (Code of Practice for Slating and Tiling) requires battens to be:
- Graded: visually or machine graded to BS EN 14081 or BS 5756. The grading mark must be visible on each length, or the supplier must provide a declaration of conformity.
- Regularised or sawn: smooth enough on bearing faces to give consistent nail-pull-through resistance.
- Treated: preservative treated to Use Class UC2 (above DPC, covered, risk of wetting). In practice, almost all batten manufacturers supply pre-treated lengths as standard.
Ungraded batten — common “seconds” from some merchants — does not comply with BS 5534 and should not be accepted on site. Graded batten carries a stamp such as “BS 5534 GRADED” or the supplier’s grading declaration.
Standard Sizes
Batten cross-sections are specified by rafter span (centre-to-centre spacing of rafters) and tile/slate type. The most common sizes in UK residential construction:
| Batten Size (mm) | Rafter Span | Typical Application |
|---|---|---|
| 25 × 38 (depth × width) | Up to 450 mm c/c | Clay/concrete tiles, lighter slates |
| 25 × 50 | Up to 600 mm c/c | Standard slates and concrete tiles |
| 32 × 50 | Up to 600 mm c/c | Heavier interlocking tiles |
| 38 × 25 | Up to 450 mm c/c | Same as 25×38, rotated orientation |
| 50 × 38 | Counter-batten | Over breathable membrane on rafters |
Note: BS 5534 tables specify minimum thickness and width as a function of rafter spacing and batten overhang. Always verify against the relevant table in the standard — the values above are typical but not exhaustive.
Batten Gauge (Spacing)
Gauge is the centre-to-centre distance between battens, which directly controls the exposure (the visible face) of each tile or slate. It is calculated from the tile dimensions and the required headlap:
Gauge = (Tile length − headlap) ÷ 2 (for single-lap tiles)
Gauge = Slate length − headlap (for double-lap slates, where each course covers two courses below)
Minimum headlap is determined by roof pitch and exposure zone (BS 5534 Table B.1). Common worked examples:
| Tile/Slate Type | Length (mm) | Pitch | Headlap (mm) | Gauge (mm) |
|---|---|---|---|---|
| Spanish slate 500 × 250 | 500 | 30° | 80 | 420 |
| Welsh slate 400 × 200 | 400 | 30° | 75 | 325 |
| Concrete interlocking tile | 420 | 35° | 75 | 345 |
| Clay plain tile | 265 | 40° | 65 | 100 |
| Fibre-cement slate 600 × 300 | 600 | 25° | 90 | 510 |
Gauge must be consistent — varying by more than ±3 mm across a rafter bay will result in visual banding on the finished roof and can compromise headlap at the tightest point.
Counter-Battens
Counter-battens are vertical (parallel to the rafter slope) members fixed directly over the rafter and under the horizontal tiling battens. Their purposes:
- Drainage channel: creates a clear air and water path behind the tile batten, allowing any water that passes the tile to drain freely to the eaves without pooling on the underlay.
- Ventilation: when used with a breathable LR1 membrane, the gap created by the counter-batten provides the recommended 25–50 mm ventilation path in cold roof assemblies.
- Membrane protection: lifts the batten nail line off the underlay surface, preventing nail point damage to the membrane.
Counter-battens are mandatory in some roof system specifications (particularly with high-performance underlays) and strongly recommended by BS 5250 in cold roof configurations.
Common counter-batten size: 50 × 38 mm treated softwood, fixed at 600 mm centres along the rafter line with ring-shank or spiral nails. Depth should match or exceed the horizontal batten depth to provide adequate drainage clearance.
Preservative Treatment
All roof battens should be treated to UC2 (Use Class 2: interior, covered, risk of occasional wetting). This is typically a CCA (chromated copper arsenate) or organic-solvent treatment applied under pressure. End cuts on site should be retreated with a brush-applied end-grain preservative.
Battens that are inadequately treated in roofs with ventilation deficiencies have historically been a major cause of premature decay — particularly on north-facing slopes and in high-rainfall regions of Scotland and Wales.
Cost per Metre
UK merchant pricing (2025–2026), ex-VAT, for graded treated softwood:
| Size (mm) | Cost per Linear Metre | Notes |
|---|---|---|
| 25 × 38 | £0.30–£0.50 | Budget batten, ensure grading mark |
| 25 × 50 | £0.35–£0.60 | Most common residential tiling batten |
| 32 × 50 | £0.45–£0.70 | Heavier tile applications |
| 50 × 38 counter-batten | £0.50–£0.90 | Often priced as 38 × 50 |
For a typical semi-detached house (80–120 m² of roof area), batten material cost is typically £150–£350 including counter-battens — a minor fraction of total roofing cost.
Fixing Requirements
BS 5534 specifies fixing of battens to rafters:
- Minimum two nails per rafter crossing.
- Nails must be hot-dip galvanised or stainless steel (A4 grade in marine environments).
- Minimum nail length: 2.5 × batten depth (e.g. 65 mm nails for 25 mm batten).
- Butt joints between batten lengths must fall over a rafter — never in the span.
- At verges and eaves, battens require additional fixing to prevent wind uplift.
Building Regulations
Part A (Structure) is the primary applicable part — the batten system is part of the roof structure that must safely transfer tile loads, including wind uplift, to the rafter. BS 5534 is cited as the relevant standard in Approved Document A. Any warranty provider (NHBC, Premier Guarantee) will inspect grading marks and treatment during frame/roof stage inspections.
