Clay and concrete roof tiles hang on horizontal battens nailed across the rafters. On many roofs, vertical counter-battens run along each rafter first, over the underlayment, to create an air gap that lets water and moisture drain away. This calculator works out the length of battens and counter-battens, the number of pieces and the cost.
The formulas
- Batten rows per roof plane = slope length ÷ tile gauge, rounded up, + 1
- Battens = rows × roof length × number of planes × (1 + waste)
- Counter-battens = (roof length ÷ rafter spacing, rounded up, + 1) × slope length × number of planes × (1 + waste)
The gauge is the distance between battens, set by the tile’s exposed length. It is printed in the tile maker’s instructions and depends on the roof pitch.
Example
A gable roof 40 ft long with two planes, 16 ft from eaves to ridge, with a tile gauge of 13.5 in, needs 16 rows of battens per plane: about 1,408 ft of battens with 10% waste. Counter-battens over rafters at 24 in centers add about 739 ft. In 12 ft pieces, that is 118 battens and 62 counter-battens, about $1,288 at $0.60 per foot.
Typical gauges
| Tile type | Typical gauge |
|---|---|
| Interlocking concrete tile | 13 to 14 in |
| Flat interlocking clay tile | 12 to 14 in |
| Spanish or S tile | about 13 to 15 in |
| Plain clay tile (double lap) | about 4 in |
Good practice
- Use pressure-treated battens sized for the rafter spacing, often 1 × 2 or 1 × 3 at 16 to 24 in centers.
- Start with the first batten set so the bottom tile row overhangs into the gutter correctly.
- Snap chalk lines to keep the rows straight and the gauge even from eaves to ridge.
- Stagger joints between battens and make them land on a rafter.
Limits
Hips, valleys, dormers and roof windows change the layout: add more waste for complex roofs. Follow the tile maker’s installation guide and local building code for wind uplift and fixing requirements, which can call for extra nails or clips near edges and ridges.