Dial Herco

These are the wooden members attached directly to the foundation walls upon which the rest of the building sits.
The sills of today’s homes are nearly always built with pressure-treated lumber — that is, lumber treated chemically to repel moisture. This keeps the sills nice and dry, unaffected by the moisture that inevitably migrates up the concrete foundation. But pressure-treated lumber has come into general use only in the last fifteen years, so if you’re looking at a house older than that, you should pay special attention to the sills.
The problem is that if sills are too close to the ground or exposed to frequent drenching by improperly installed rain gutters or clogged drainage pipes, they rot. When they rot, they lose their load-bearing ability, compress under the weight of the house, and cause many problems.
The list of symptoms of rotted sills is as long as your arm:
sagging floors, windows that won’t open or close smoothly because their frames are out of square, porches that have slipped away from horizontal. Carpenters generally love the problems posed by rotted sills and are astonishingly skillful at fixing even the most hopeless-seeming cases, but it’s major surgery. Normally the exterior siding will have to be removed and replaced because it too has rotted. Then the sheathing will also need to be removed, exposing the studs. If the damage isn’t too severe, the studs can be saved and nailed back to the new sill, but occasionally the rot is so extensive that the studs themselves have to be cut back and bolted to new stud ends.
Besides removing the rot and replacing the sills, studs, sheathing, and siding, the carpenter must also, of course, diagnose and correct the cause of the problem. Was it a leaking root? Was it the grade around the house? It doesn’t make much sense to go to the expense of repairing the sill problem if you’re not going to take steps to prevent a recurrence.