We live in a one-floor, 25-year-old condo. When the leaf blowers come in the fall, we get a small amount of litter on the basement floor near one corner. We have searched for this opening in the dark basement when the sun is shining on the foundation, but can see nothing. Is the sill a place where airflow occurs? If so, how can the airflow be blocked, and whom should we hire to fix it?
We would like the sill inspected and filled on all our three outside walls and connection points with our neighbor. The condo association will not pay for this; it denies there is a problem. We are happy to fix it if we knew how.
There are several sills in every house. Among them: window sills, door sills (often called thresholds), and timbers that sit on the stone or concrete foundation. The stones or concrete may be rather uneven, leaving gaps (large or small) between the sill and the foundation. Gaps are hidden by the siding that covers up the joint. Sometimes you can feel behind the sheathing boards and siding. You can fill the gaps with an adhesive caulk if you can reach them, but it may be easier to fill them with caulk or fiberglass insulation from the inside.
Another way: Staple fiberglass insulation with paper backing against the sill, making sure the insulation seals the joint. Insulating the basement ceiling will also make a difference and prevent a goodly amount of heat loss in winter and cooling loss in the summer.