In cases where only a portion of a clapboard is damaged, use a speed square to mark a new joint (Image 1) and cut off the damaged portion with a circular saw (Image 2).
In this case, removal of the damaged boards revealed a section of the sill, beneath the clapboards, that had been damaged by termites (Image 3).
The termite-damaged area will have to be cut out entirely and replaced with a new section of wood. A custom-cut piece is made by joining together two pieces of pressure-treated lumber to achieve the proper dimension. The treated lumber is resistant to insect infestation.
To restore the termite-damaged area, use a reciprocating saw to score the outline of the wood that needs to be removed (Image 1). Then, follow that outline with a circular saw and make vertical cuts with the reciprocating saw (Image 2). Finally, use a wood chisel and mallet to chisel out the damaged wood that remains.
With the length and width of the removed sill, cut two pieces of treated lumber that can be nailed together to achieve the thickness you need.
Place the replacement sill into the hole (Images 1 and 2), fitting it in tightly with a sledgehammer.
Nail it into the surrounding sill and to further solidify the patch, drill holes around the perimeter and fill each hole with epoxy (Image 3). This will help strengthen the delicate wood that surrounds the repair.
We used cedar siding to replace the rotted clapboards. First, to help avoid any future insect damage, back prime the cedar with oil based primer (Image 1).
Before the siding can go up, 1x4 starter strips of treated lumber should be nailed to the sill where the lower most course of siding will go up (Image 2).
Cut the cedar siding to the lengths needed using a miter saw and then nail it to the starter strips. Measure the depth to make sure it is consistent with the existing courses above.
After the first course of siding is up (Image 1), you can start adding the rest, slipping them under the courses above and nailing in place (Image 2).
Caulk the end joint and prime the front of each clapboard (Image 3).
Allow the primer to dry and you're ready for the final coat of paint.