Getting the spacing even
Board and batten goes wrong in the math. You want 16″ spacing, the wall is 11′ 9 3/8″, and somewhere around the eighth batten you realize the last gap will be 4 inches. The fix, and the formula the calculator uses, is to choose the number of gaps first and let the spacing come out of the wall.
gaps = round ((wall width − batten width) ÷ target spacing)
on center = (wall width − batten width) ÷ gaps
gap between battens = on center − batten width
battens = gaps + 1
Here's a 12-foot accent wall (144″) with 2 1/2″ battens at a 16″ target. (144 − 2.5) ÷ 16 = 8.84, which rounds to 9 gaps. 141.5 ÷ 9 = 15.72″, so the battens land 15 3/4″ on center with a 13 1/4″ gap between them, and you need 10 battens. With a 2 1/2″ top rail on an 8-foot wall, each vertical is 93 1/2″ long.
The marks table gives you each batten's left edge measured from the corner. Mark them all on the top rail or the wall before you nail anything, and stand back to check the layout around outlets and switches.
Building an accent wall
- Paint first, then batten, then caulk and paint again. Priming the wall and the battens before they go up means you're only cutting in the edges at the end.
- Find the studs before you mark. Battens that land on a stud get nailed there. The rest hold with construction adhesive and brads driven at opposite angles.
- Deal with the baseboard. Either leave it and run battens down to sit on top, or pull it and use a bottom rail the same thickness as the battens. Battens thinner than the baseboard look stuck on.
- Plumb beats measured. Corners are rarely plumb. Measure your marks along the top, then set each batten with a level.
Exterior board and batten siding
On real siding, wide boards, usually 1×10 or 1×12, hang vertically with a small gap between them, and a narrow batten covers each seam. The spacing isn't your choice: it's the board width plus the gap. The calculator counts boards across the wall, tells you how wide to rip the last one, and puts a batten over every seam. Once you have the count, price the siding by the board foot.
If the last board comes out very narrow, shift the layout so you rip a little off the first board too. Two medium rips at the corners look better than one skinny strip.
Fastening matters more than spacing here. Nail each board on its own and put the batten nail through the gap, or into one board only, so neither board is pinned to its neighbor. Follow your siding maker's spec for nail type, length and spacing, and make sure there's wall framing, blocking or furring behind every row.
Counting shiplap instead
Shiplap and tongue-and-groove are counted by the face that shows, not the board's full width. A 1×8 shiplap board usually covers around 6 3/4″ to 7″ once the laps overlap, but profiles vary, so check the face width of yours. Then divide the wall area by what one board covers:
boards = wall area ÷ (exposed face × board length)
For a 12 × 8 foot wall (96 square feet) with 8-foot boards and a 7″ face, each board covers 4.67 square feet. That's about 21 boards, or 23 with 10% for waste. Subtract big windows and doors before you divide.