Lap siding, also called horizontal siding or clapboard, is usually beveled, meaning that the bottom edge is thicker than the top. As its name implies, an upper siding board laps over the board below it by at least 1 inch and usually by 2 inches or so. Nails may be hidden, meaning they are driven into the upper portion of a board so they are covered by the lower part of the board above it. Another option leaves exposed nail heads; the nails are driven into the lower portion of a board so they go through the upper portion of the board below.

If you are planning to paint your siding, it’s a good idea to prime all the pieces on all sides before installing them; that way, the backsides will also be protected against rot.

Install cement lap siding in much the same way as you would siding made from wood. However, it is recommended that you leave 1/8-inch gaps at the ends of the boards to allow for expansion; apply caulk to the gaps.

In older installations, lap siding is carefully bevel cut to make perfect outside corners. This makes for a classic look but calls for very good carpentry skills and boards that are certain not to shrink. The method discussed here is an easier and more common one— installing corner trim first and then butting the siding to it.

Wall prep
The walls should be stripped of all previous siding and covered with a code-approved building paper or roofing felt. The surface should be fairly smooth, though the siding will follow along any contours. Install the building paper carefully so that it covers all surfaces. If possible, it should go under all trim pieces.

Around windows and doors, you may want to install self-stick flashing and metal flashing before applying the trim to be sure water will not infiltrate. Consult with local pros or your building department for the best methods in your region.

Some installers install vertical strips of roofing felt over the studs; these help you locate the studs, and they help seal the nail shanks to prevent moisture penetration.

Layout
Determine how the boards will look where they meet an eave at the top. You may be able to install a trim piece there after the siding is installed, or you may need to cut the siding to fit precisely.

Determine the desired “reveal”—the vertical width that will be exposed. For instance, you may have 8-inch-wide boards with a 5 1/2-inch reveal. If you buy siding that has installation grooves, such as shiplapped or bevel- rabbeted siding, the reveal will be determined by the rabbet or the shiplap; you simply stack boards on top to get a consistent reveal. On non-grooved siding, you will need to constantly check the reveals using a special tool or a tape measure. The smaller the reveal, the more classic the appearance will be.

In most cases, the siding will wrap all the way around the house. The last boards must meet at the same level or the installation will look unprofessional. This means you must mark level lines all around the house. Use a water level, line level, or transit level to make these layout lines.

You may want to modify the layout so you have full-width boards at the top of windows or doors, especially if you have a number of windows at the same height. It often works to move down the second-from-the-bottom siding piece so that the bottom piece has a smaller reveal than the others.

Cutting & fastening
If you do not own one, buy or rent a power miter saw or a radial-arm saw. You can cut using a circular saw but the going will be slow.

If the house’s sheathing is plywood, you can drive nails just about anywhere, but it is best to drive nails into studs to ensure firmness. If the sheathing is fiberboard, gypsum, or other soft material, then you can fasten only to studs.

Consult the manufacturer’s literature and with local builders for the best type of nails to use. Siding nails typically are thin, with small heads. Ring-shank nails hold better than standard nails. Wherever you will drive a nail less than 3 inches from a board’s end, drill a pilot hole first to prevent cracking the board.

1) Trim and bottom piece. To trim an inside corner, nail a piece of 1x1 (which you can rip yourself from a 1x board) or 2x2. At an outside corner, use a 1x3 and a 1x4, or a 1x2 and a 1x3. (The side with the narrower piece will look nearly as wide as the other because of the thickness of the other piece.) Install all trim pieces around windows and doors. At the bottom, install a starter strip supplied by the manufacturer, or install a 1x2. See that the starter board is level. Go all around the house with the starter board to make sure you will come out at the same level when the boards meet at the final corner.
2) Bottom board. Chalk a line indicating the top of the bottom board. Cut the board to fit snugly; if it is longer than 6 feet, it is best if you have to slightly bend it to make it fit between trim boards. Align the board with the chalk line and drive nails every 6 inches or so into the starter strip.
3) Lay out with a story pole. To help with the layout, make a story pole. This is simply a board marked with evenly spaced lines that indicate the reveal you have chosen. Hold the story pole at the correct height at each inside and outside corner and mark the trim boards for the locations of the siding board bottoms.
4) Mark trim boards. Again using the story pole, mark the trim pieces around windows and doors. Be sure to hold the pole at the exact same height every time you mark trim boards.
5) Second piece. Cut and position the second-from-the- bottom piece so it aligns with the layout marks you made with the story pole. Check for level to be sure your layout marks are correct. This piece will lap over the bottom piece. In certain installations, nails are driven through the bottom of the siding, leaving the heads exposed. In other installations, nails are driven into the upper portion of the boards so they will be hidden by the succeeding piece.
6) Butt joints. If a single board will not span all the way between trim pieces, you will need to make a butt joint. Cut the boards so they meet in the middle of a stud. Test to make sure you have a tight fit and then apply caulk to both board ends. Drill pilot holes before driving in the nails.
7) At a gable. If you need to cut boards at angles, hold a T bevel tool against the trim piece and the gable to get the angle of the cut. Tighten the wing nut and use the T bevel to mark boards for cutting.