Battens and underlay
Batten set-out: equal gauge, courses and batten length
- where
- number of gauges between first and top batten
- distance from the eaves batten to the top batten (mm)
- maximum gauge (mm)
- equal batten gauge (mm)
- batten courses per slope
- total batten length (m)
- length of each batten run (m)
- number of slopes like this
- joints and offcuts allowance (%)
- batten lengths to order
- stock length of one batten (m)
Explain this equation
Sets out equal battens between a fixed bottom and top batten without going over the tile's maximum gauge, then totals the batten to order.
D is the distance to be split up. Dividing by the maximum gauge g_m and rounding up gives the fewest spaces n that keep every gauge within the limit; D/n is then the actual equal gauge. There is one more batten than spaces. Each batten runs the eaves length E, on every slope n_s, plus a percentage for laps and offcuts. Dividing by the stock length and rounding up gives the lengths to buy.
Rounding the number of spaces up, not the gauge, means the gauge only ever gets slightly smaller, which keeps the headlap safe.
Sense check: 4500 mm at a 345 mm maximum needs 14 spaces of about 321 mm and 15 battens. On two 10 m slopes with 10% that is 330 m, or 69 lengths of 4.8 m.
Watch out: D is measured between batten centres or tops consistently, not from the fascia. Allow for the eaves course and any top course detail first.
Gauging out a slope: divide the distance between the first and top battens into equal spaces no larger than the maximum gauge, then total up the battens.
Enter your values to see the result.
Good to know
Fix the eaves (first course) batten and the top batten positions from the manufacturer’s eaves and ridge details first, measure between them on the rafter, then mark equal gauges. Double-lap roofs need an extra eaves batten for the under-eaves course: add one course per slope. BS 5534 and the manufacturers give batten sizes by rafter centres, for example 38 × 25 mm up to 450 mm centres and 50 × 25 mm up to 600 mm for Marley Modern. Battens must be graded to BS 5534 and joined over rafters.
Common mistake
Laying every course at the maximum gauge and squeezing whatever is left into the top course. Equal gauging keeps the headlap at or above the minimum everywhere.
Limits
One straight run of battens per course. Hips and valleys shorten the courses: on hipped roofs work from the area (battens per m² × area) instead.
Sources
- Marley Modern concrete interlocking tile: technical data (420 × 330 mm, 292 mm cover width, 345 mm max gauge, 9.9 tiles/m², 2.9 m battens/m², 50 kg/m²)
- BS 5534:2014+A2:2018 Slating and tiling for pitched roofs and vertical cladding. Code of practice (BSI)
- BS 8000-6 Workmanship on construction sites. Slating and tiling of roofs and walls. Code of practice (BSI)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the roof covering manufacturer’s fixing specification, BS 5534, BS 8000-6, BS 6229, the Lead Sheet Training Academy guidance and Building Regulations. Wind uplift and structural design need a competent designer.