Formula
The wall starts and ends on a board. There are n boards and n − 1 gaps. n is the count that puts the gap nearest the one you asked for, and then the gap is recomputed so the boards fill the wall with nothing left over.
n ≈ (wall + desired gap) ÷ (board + desired gap)
gap = (wall − n × board) ÷ (n − 1)
overlap each side = (batten − gap) ÷ 2
End battens are face-applied. They do not enter the gap math. The diagram draws the boards, the gaps, and a batten centered on each gap.
Worked examples
96 inch wall, 7.25 inch boards, 1 inch gap, 3.5 inch battens. Twelve boards fill it. The gap opens to (96 − 12 × 7.25) / 11 = 0.818 inch. Eleven battens. Overlap is (3.5 − 0.818) / 2 = 1.34 inch per side.
Same wall with end battens. Still 12 boards and the same gap. The batten count becomes 13.
Reference
Eight-foot height, 7¼ inch boards, 3½ inch battens, a 1 inch target gap, no end battens. The gap in the table is the one that actually fits.
| Wall | Boards | Battens | Gap |
|---|---|---|---|
| 48 in | 6 | 5 | 0.9 in |
| 72 in | 9 | 8 | 0.844 in |
| 96 in | 12 | 11 | 0.818 in |
| 120 in | 15 | 14 | 0.804 in |
| 144 in | 18 | 17 | 0.794 in |
Questions
How many boards and battens cover a wall?
Start and end on a board. Pick a board count so the gap between boards is close to the gap you asked for, then recompute that gap so the boards fill the wall exactly. Battens cover the gaps. On a 96 inch wall with 7¼ inch boards and a 1 inch gap, that is 12 boards and 11 battens.
Do end battens change the spacing?
No. End battens sit on the face of the first and last boards. They add two pieces to the batten count and they do not change the gap. Leave them off if the boards already die into a corner.
How much should a batten overlap the boards?
Overlap on each side is (batten width − gap) ÷ 2. A 3½ inch batten over a 1 inch gap overlaps about 1¼ inch per side. Under ½ inch, the boards can move enough to show the seam. If the batten is narrower than the gap, it cannot cover the joint.
How many sticks do I buy?
The stock length is the board you can buy, in the same units as the wall height. An 8 foot wall and 8 foot stock is one stick per board and one per batten, if you do not want a mid-wall splice. A shorter stock is counted as spliced pieces.
Sources
- Even board-and-batten layout: n boards, n − 1 gaps, gap recomputed so the courses fill the wall. Overlap = (batten − gap) / 2.