This story presents solutions for repairing various problems with lap siding.
If a wood clapboard is rotted in a small area, you can apply wood hardener and patch with wood filler or epoxy. If the damaged area is large, you'll have to replace the board or a part of the board. You can cut a board almost anywhere if your sheathing is solid plywood or OSB, but if the sheathing is not solid, it must be cut in the middle of a stud so the joint can be firmly nailed.
If there is widespread rotting, the area behind might be getting wet and the problem might be with the building paper or the way the siding was installed.
Siding that is buckling or pulling away from the wall may be insufficiently nailed. Try driving long nails or screws into studs.
Beveled siding made of pressed board, which is no longer made, is notoriously unstable and weak. If it is warping, buckling, or flaking apart, it needs to be removed and replaced.
Less than an hour for most repairs
Hammer, tape measure, square, flat pry bar, putty knife, keyhole saw, caulking gun, paintbrush, sanding block, utility knife
Cutting, measuring, fastening
Check the siding closely for further damage to determine how large a section of siding needs to be replaced.
Wood filler, wood hardener, caulk, exterior or polyurethane glue, nails or screws, roofing felt, sandpaper, primer and paint
If the siding board above has exposed nails that go into the board that you want to remove, pry away the siding board above and then tap it back in. The nailheads should pull out to the point where you can grab and remove them with a pry bar. Tap in shims to hold the board away from the wall. You will probably need to do this for a fairly wide area on each side of the damage. Pry out the nails holding the damaged siding. If you are removing an entire board, pull out all the nails and pry out the board.
To cut out a damaged area, use a square and a utility knife to scribe cut lines on each side of the damage. Using a circular saw set to the thickness of the siding, complete as much of the cut as you can without cutting into the siding above the cut. Be careful not to damage the sheathing.