Coverage
Single-lap (interlocking) tiles per m² and battens per m² from gauge
- where
- batten gauge (mm)
- tile length (mm)
- headlap (mm)
- tiles per m²
- effective cover width (mm)
- battens per m² (m/m²)
Explain this equation
Works out the batten gauge for interlocking concrete or clay tiles, then how many tiles and how many metres of batten each square metre of roof needs.
With single-lap tiles each course only overlaps the one below by the headlap h, so the exposed length up the slope, the gauge g, is the tile length less the headlap. Across the roof each tile covers its effective width c, which is less than its full width because of the interlock. Each tile therefore covers g × c square millimetres, and a square metre is 1,000,000 mm². One batten run is needed per gauge, so a metre of roof height needs 1000 / g metres of batten.
Simple coverage: area of a square metre divided by the area each tile actually covers.
Sense check: a 420 mm tile with a 75 mm headlap and 292 mm cover gives a 345 mm gauge, about 9.9 tiles per m² and 2.9 m of batten per m².
Watch out: many interlocking tiles have a fixed or narrow gauge range. Use the manufacturer's minimum headlap for the pitch and exposure, not a guess.
Coverage of interlocking tiles: the gauge is the tile length less the headlap, and each tile covers one gauge by one cover width.
Enter your values to see the result.
Good to know
Use the cover width from the manufacturer, not the overall tile width: the side interlock overlaps. The gauge found here is the maximum; on site the actual gauge is set out equally up the rafter (see the batten set-out calculator), so it is often a little less. Marley Modern: 420 mm long, 292 mm cover, 75 mm headlap at 22.5° and over gives 345 mm gauge, 9.9 tiles and 2.9 m of batten per m²; 100 mm headlap gives 10.7 tiles/m².
Common mistake
Reducing the headlap below the manufacturer’s minimum to stretch the gauge. Headlap depends on pitch, rafter length and exposure, and is set by the manufacturer under BS 5534.
Limits
Single-lap tiles laid broken-bond or straight-bond on battens. Some tiles have a fixed (non-variable) gauge: use the manufacturer’s figure. For plain tiles and slates use the double-lap calculator.
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)
- Marley: Roof tile sizes and how many roof tiles per square metre
- BS 5534:2014+A2:2018 Slating and tiling for pitched roofs and vertical cladding. 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.