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.