The most familiar type of wood siding is the clapboard, a form of lap siding that’s also called bevel siding. Clapboards have a triangular cut: thinner at the top and wider near the lower, more exposed part of the board. Clapboards can also be rabbeted, or notched at the bottom so that the edge of one board overlaps the one next to it in a flush joint. Traditionally, clapboards are installed with joins cut at an angle (scarfed), but they can also be butt-joined.
On an old house, time and gravity have added a bit of longitudinal rhythm to the original crisp lines, so replacing or hanging clapboards calls for skillful layout work. While one person usually can repair or replace a few damaged boards solo, a full-scale re-siding usually requires a crew of at least three: one person to make the cuts on a power miter saw, and two people to hold, line up, and nail each board in place. Here are some of the techniques restoration professionals typically recommend:
Establish Points of Reference
Before removing the existing siding, pinpoint a horizontal reference line (1 on the drawing on the opposite page) that runs the full length of the wall, such as the lowest point of a frieze at the top, or a skirting board at the bottom. Then make a long, square 1" x 2" furring strip tall enough to run from the lowest course of clapboards to the frieze or roofline. This is called a storey pole (2). Pros use these reference points to plan the layout of the siding.
Plan the Courses
Tack or hold the storey pole against the façade using your horizontal reference. Mark the top and bottom points of windows and doors on the first elevation you intend to side on the pole. Then visually divide the storey pole into three sections: the area above the windows, the area between the top and bottom of the windows, and the area below them (3). You’ll break these sections down into evenly spaced courses once you’ve set the exposure, the result of how much one clapboard overlaps the next.
Set the Exposure
The overlap for each row of clapboards should be reasonably consistent and in keeping with the look of the original siding. As a rule of thumb, there should be at least 1" of overlap from one board to the next so that a nail through the top clapboard also runs through the one below it, and into the sheathing at least 1¼" deep. In a perfect world, the courses should break conveniently right at the tops and bottoms of window and door casings.
Once you have a figure for the exposure—say, 4", typical on many frame houses built in the 19th and early 20th centuries—divide each of the three sections on the storey pole into evenly spaced courses, marking as you go (3). Adjusting individual clapboards up or down by as much as ¼" for a 4" exposure shouldn’t be noticeable. Once again tacking the storey pole to the side of the house, use your marks to snap chalk lines for each course.
Fit the Windows
Fitting clapboards is a bit like doing a puzzle where the difficult parts come first. Start by tacking clapboards into position at the tops of doors and windows and underneath sills (4). (You will probably need to cut a notch in the one below the window; use the casing to scribe it.) Using the storey pole, check to make sure the exposure for the boards you’ll attach between the windows will fall where you want them to. Then tack on the clapboards, beginning at the top of the window and working down.
When butting clapboards at corner boards or window frames, first measure the length of the space (using a clapboard that’s slightly longer as a ruler) and mark it with a pencil. Allow at least 1⁄16" to 1⁄8" of overage, which can be cut or trimmed away when the board is fitted into place.
Lay the Courses
For a traditional base below the first row of clapboards, install a watercourse: a flat, 1" x 12" board with a 3" bevel at the top. The board supports the first clapboard at the correct angle while providing a skirt for the wall. Working in lengths from 6' to 8', lay boards from the bottom up. Lay the initial course to match the baseline of the wall, which may wave up and down slightly (5). To help smooth things out, snap a chalk line between the two corner boards to establish a line to follow. As you work, place boards strategically so that joints are staggered 12" to 18" apart from row to row (6); this will help keep out water. Tack the clapboards in place for most of a section to make sure all the boards are properly positioned.
Nail It On
Once everything is in its proper place, it’s time to nail up the wood. Use “splitless” ring-shank siding nails with thin shanks, blunt points and ridged heads, which help prevent splitting. Predrill nail holes, spacing them about 20" apart. If you’ve used scarf cuts, the nails should be at least ½" from the edge of the boards, and at least 2" from the board ends. (Butt-cut clapboards should be at least ½" from any edge.) When you reach the top of the wall, with any luck the last clapboard will fit effortlessly against the frieze.
Planning the Layout
Establishing horizontal (1) and vertical (2) points of reference will aid in laying out clapboards that appear straight and true, even when the walls are not. Use the vertical reference, or storey pole (2, 3) to plan courses. Fit siding above and below windows (4) first, then lay clapboards from the bottom up (5). Stagger the boards to keep rain from channeling down the cut edges (6).
A Short Course on Cladding: Part 1