Two different walls with the same name
Board and batten covers two constructions that look similar from the road and are counted completely differently. The traditional one is wide boards run vertically with a narrow batten over every seam. The modern one is a sheet product, usually a panel or a flat fibre cement sheet, with battens applied on top at a chosen spacing purely for the look. In the first the batten has a job; in the second it is a decoration and the spacing is yours to pick.
That distinction decides the arithmetic. In the board version the spacing is fixed by the board width plus its gap, and the only question is what happens to the last board at the far corner. In the batten version the spacing is a free variable, and the only question is what number of bays divides the wall closest to the look you want.
The last board is where a wall falls apart
Take a 24 foot elevation and 1x12 boards, which measure 11-1/4 inches, with a quarter inch gap between them for movement. The repeat from one board to the next is 11-1/2 inches. Twenty-four feet is 288 inches, and 288 divided by 11.5 is 25.04. So twenty-five boards fit and the twenty-sixth is a quarter inch sliver against the corner board.
A quarter inch of board under a two and a half inch batten is invisible until the batten shrinks or the corner trim moves, and then it is a permanent stripe. The fix costs one saw pass per board. Divide 288 by 26 to get an 11.08 inch repeat, take the quarter inch gap back off it, and rip every board to a 10.83 inch face. The count is identical, the spacing is uniform, and the wall reads as though the house was designed around the board width.
The same logic runs in reverse if the remainder is nearly a full board. A last board at ten inches next to boards at eleven and a quarter is close enough that most eyes forgive it, and ripping twenty-six boards to save it is not obviously worth the afternoon. The calculator flags the sliver case and leaves the judgement to you in the middle.
Picking a batten spacing that reads right
On the panel version the spacing is a design decision before it is a material one. Narrow spacing makes a wall look taller and busier and eats battens; wide spacing reads calmer and lets the panel joints show more.
| On centre | How it reads | Battens per 24 ft wall |
|---|---|---|
| 12 in | Fine, vertical, farmhouse density | 25 |
| 16 in | The common middle, matches stud lines | 19 |
| 20 in | Calmer, reads more modern | 15 |
| 24 in | Wide and spare, panel joints more visible | 13 |
Those counts assume a batten at each corner. Whether you want one there depends on how the corners are trimmed: with corner boards the end batten is usually redundant and looks doubled up, and without them the batten is what finishes the edge. The calculator has a switch for it because it changes the count by two on every elevation and people forget it on all four.
Two practical points that the spacing number hides. A batten that lands within an inch of a window or door casing looks like a mistake rather than a rhythm, so check the openings before committing to a bay count. And the spacing should be worked out wall by wall rather than once for the house, because a 24 foot elevation and a 31 foot elevation will not both divide evenly at the same number.
What sits behind it
Vertical cladding puts every seam in a line that water runs straight down, which is a different problem from lap siding where every course sheds outward. The battens cover the seams, but the battens are not the waterproofing and were never meant to be. What keeps the wall dry is the drainage plane behind the cladding and the flashings at every horizontal interruption, and those have to lap so that water leaving one lands on the face of the next.
Getting that order wrong produces a wall that looks completely finished and leaks quietly for years, which is the single most expensive mistake available on an exterior. This page counts boards; it does not tell you how to build the assembly, and the lapping order belongs with the instructions for the specific products you have bought and with whoever inspects the work. The house wrap calculator and the wall condensation risk calculator deal with the layers behind the cladding.
Vertical boards also need something to fasten to, which on a wall sheathed for horizontal siding may mean furring or blocking that is not there yet. If you are adding a vented cavity at the same time, the rainscreen furring calculator counts the strips. For the horizontal cousin of this page see the lap siding course layout calculator, and for the interior version of the same look the wall panel calculator works from a reveal rather than a batten line.
Questions people ask
How wide should the gap between boards be?
It depends entirely on what the boards are made of and how wet they are when they go up. Solid wood boards move across the grain with moisture and a wide board moves a lot: a nominal 1x12 can change width by a quarter inch or more between a dry winter and a humid summer, which is why the gap exists and why the batten is wide enough to cover it at both extremes. Engineered and fibre cement products move far less and their instructions give a specific gap. The quarter inch default here is a common figure for wood, not a specification. If you are working in solid wood, the wood movement calculator will give you the seasonal range for your species and width.
Should there be a batten at each corner?
It is a look rather than a rule, and it hinges on whether you are using corner boards. With corner boards, an end batten sits immediately beside a much wider trim piece and reads as a doubled-up edge, so most people stop the battens short. Without corner boards, the end batten is what closes the elevation and it has to be there. The count difference is two per wall, which over four elevations is eight pieces, enough to matter on an order.
Can I put battens over existing siding?
People do it, and it is where the seams and the flashings get interesting rather than where the battens do. Fastening through an existing cladding into whatever is behind it changes the fastener length, changes the depth every window and door trim has to stand proud by, and traps whatever the old wall was doing behind a new layer. Whether that is sensible depends on what the existing wall is, how dry it is, and what your building department says about layering cladding, none of which is a calculator question. If the existing siding is from before the late 1970s, testing it for asbestos before you drive fasteners through it is the first step rather than the last.
How do I handle a gable above the wall?
Run the wall layout first and carry its batten lines straight up into the gable so the verticals line through, then work the gable as its own piece with angled top cuts. The temptation is to lay the gable out independently, because it is a triangle and the widths are all different, and that produces two sets of vertical lines that nearly agree, which is worse than either one alone. Enter the gable width as the run only if the gable is over a different wall entirely.
Does the calculator account for openings?
Not by deducting them, deliberately. Boards and battens run past a window rather than stopping at it, and the pieces above and below an opening still have to be cut from full lengths, so deducting the opening area understates what you buy. What openings do change is where a batten lands, and that is worth checking by eye against the spacing this page gives you before you order anything. For openings as an area deduction across a whole house, the siding calculator handles it that way.