How to Fix a Rotted Exterior Wall

Select replacement wood siding that is similar in texture to the siding on the house. Measure the width of the exposed boards and add 1 inch for overlap. Purchase boards long enough to replace the piece of siding you are removing. Select better-quality knot-free, quarter-sawn siding, if available, because it is easier to paint.

Make a horizontal cut the length of the board you are replacing about halfway up from the bottom, or butt, edge. Take care not to cut into the builder's felt behind the wood.

Insert a pry bar under the butt edge next to a nail. Tap the pry bar gently with a hammer to work the nails holding the board loose. Try not to damage surrounding boards as you work, or you may have more boards to replace.

Snap the butt edge free once the nails are loose. Set the broken piece aside to use as a template for the replacement board.

Examine the builder's felt underneath the board for signs of mold or moisture. If you see signs of damage, gently pull away the builder's felt and examine the sheathing underneath. If it has damage, cut out the damaged wood with a jigsaw and replace it with exterior-grade plywood sheathing. If there are signs of damage, you may need to remove several boards to complete this step. Seal holes in the builder's felt with roof repair cement.

Pull out the nails that held the butt edge of the siding in place. Use the pry bar to pull out the nails from the butt edge of the board above the one you are replacing. Run a hacksaw between the siding and the sheathing to cut out the nails if you can't pull them.

Lay the new piece of siding on a flat work surface. Place the butt edge you removed in Step 4 on top of the new siding. Mark the length you need to cut the new siding, using the old piece as your guide. Score the new siding with a utility knife to mark it, then cut it with a handsaw.

Run a bead of paintable latex caulk along the ends of the adjacent siding pieces. Push the thinner edge of the new siding under the butt edge of the siding piece above the gap. Line up the butt edge of the new piece with the rest of the siding in that row. Wipe off any caulk that oozes out of the seam.

Place stainless steel ring-shank 7d or 8d nails about 3/4 inch up from the butt edge and about 1 1/2 inches from each end. The nails need to be long enough to pass through the siding layers and into the sheathing. Align the new nails with other nails in the existing siding. Avoid causing dents in the wood with your hammer. Replace nails in the butt edge of the siding above the replacement piece.

Set the nails below grade on the siding, using a nail set. Fill any holes with wood putty.

Apply a coat of primer to the siding and allow it to dry. Paint the replacement board with two coats of paint; allow each coat to dry thoroughly.