Sealing rim joist air leaks can make a big improvement in your home’s energy use—especially in the winter. Use caulk or expanding spray foam to seal areas between the sill plate and foundation, in cavities between rim joists and all electrical penetrations, and around pipes and ventilation ducts that pass outside of the house.
Types of Rim Joists
Types of Caulking
Caulks come in a wide variety of types. Before purchasing one, read the label to be sure it is suitable for the material to be sealed. Some cannot be painted, and others are only for inside use. An important consideration in selecting a caulk is life expectancy; some last only a few years while others last 20 years or more. Since this is probably not a job you will want to repeat regularly, we recommend buying long-life products.
There are three main categories of caulks, and their prices are directly proportional to their life expectancy. As shown here, the least expensive, oil-based, has the shortest life. It works on all household surfaces, but over time, the oil seeps out and may stain surrounding materials.
Caulking Compounds Durability:
Oil-Based _ 2-3 Years
Butyl Rubber, Latex & Acrylic _ 5-10 years
Silicone, Hypalon & Polysulfide _ 10-20 years
Butyl rubber, latex and acrylic caulks last almost 10 times longer than oil-based caulking. Latex is restricted to indoor use unless painted and because it is water soluble, which means it should not be used where it can become wet. Acrylic is durable and fast-curing, but cannot be painted. Butyl rubber is water resistant, needs no paint, but may take over a week to cure.
Silicone caulks are usually your best choice. They last 20 years or more and can be used inside or out; however, they do not adhere well to painted surfaces.
Foam sealants, like polyurethane, are not true caulks but are excellent for filling large cracks. In new construction or when building an addition, seal openings around pipes and wiring before the walls are sealed (which would then conceal the cracks.)