Rim Joist Insulation

What is a Rim Joist and Why does it need to be Insulated?

The rim joist or band joist area of a home is in the basement or crawl space. It is the area where the concrete foundation meets the wood sill plate between floors. According to the Department of Energy, this area is one of the largest sources of air infiltration in a home. It is also one of the leading entry points for pests such as mice or insects. The reason this is a problem area is because there are several framing components connecting in a small area which provides many areas for air infiltration if they are not sealed properly. Secondly, these surfaces are cold on the inside of the house creating a scenario where condensation and the associated risks with long term condensation on wood surfaces.

Why Not Fiberglass for Rim Joist Insulation?

There are two main ways to insulate the rim joist. The most common way is to cut fiberglass batting insulation into squares and fit them into the cavity. This is the worst option because fiberglass is air permeable. Thus, the insulation is essentially acting as an air filter which catches some of the outdoor air contaminants such as dust and pollen while still allowing unconditioned air into the conditioned living space. The last reason fiberglass is inadequate is because it can trap moisture against the wood which can lead to mold and decay issues.

Rim Joist Spray Foam Insulation

Closed cell spray foam insulation is the best option for insulating the rim joist. Not only does spray foam insulate the rim joist area; it fully air seals all connections and interfaces from the sill plate to the sub floor. Air sealing this area prevents air infiltration, pest infiltration, and moisture buildup which prevents mold formation that could affect indoor air quality. Not all homes are the same but typically air sealing the rim joist area reduces air loss by around 10-15%.

What is the Cost of Rim Joist Spray Foam Insulation?

The cost of insulating your rim joist depends on a few factors. The main factor being the size of the area being spray foamed – the higher the square footage, the more foam is required. Other factors include insulation removal, if there is existing insulation it must be removed to be able to spray the area. The last factor is prep work required, if the area is unfinished with no obstacles the prep work is minimal which reduces cost. Finished spaces require more preparation to protect the area from any spray foam that might get on furniture, floors, walls, etc.

Call us at (816) 353-2160 today to schedule a free estimate for rim joist insulation at your home or property!