If you have an older house with fiberglass insulation around the rim joists  also called the band joist, it is time to replace it. This simple basement project is often overlooked, but insulating and air sealing the rim joists is one of the most effective energy-saving improvements homeowners can make to their homes. It also improves indoor comfort and reduces drafty rooms.

This article discusses how to use spray foam insulation to insulate rim joists, as well as tips and safety precautions.

Before installing spray foam, make sure to remove any existing drywall and insulation at the rim joist area and repair any damage or leaks. Clean the rim joist area and use a hose with water to rinse away any dirt or dust that may be stuck. After the joists are cleaned and rinsed, it is important to allow them to dry completely before proceeding with the insulation installation.

Generally, the best option for insulating a rim joist is spray foam because it is a more effective solution than traditional fiberglass batt insulation. Fiberglass is not as effective because it does not stop air flow and does not provide a vapor barrier. This means that warm moist air passes through the fiberglass, hitting cooler joists and condensing, which can lead to mold or rot of the wood. In addition, fiberglass can absorb moisture and lose its R-value over time.

Insulating a rim joist with spray foam creates an air barrier that stops outside air from entering the home and prevents moisture from seeping into the basement or crawlspace. Spray foam will also help to lower energy bills and improve home comfort and health.

Rim joists can be difficult to reach, so a homeowner should always be careful when using a power tool or applying a thick spray of spray foam. It is best to work in small sections and to spray the foam in thin layers so it has time to expand and fill gaps and cracks. It is also recommended to use backer rods in the area where spray foam will be applied. These will give the foam something to attach to, which can reduce voids in the area and ensure a good, long-lasting insulation.

When using spray foam to insulate rim joists, the homeowner should wear gloves, safety glasses and a respirator mask. It is also a good idea to work in a well-ventilated area. When using a power tool, the homeowner should read and follow the manufacturer’s instructions for operation.

Before beginning the insulation process, it is important to check with local building inspectors to be sure that this type of installation is allowed in your area. Most jurisdictions do not require a vapor barrier to be installed in the basement or crawlspace, but it is important that your rim joist insulation meets or exceeds the minimum requirements of your local building code for your climate zone.

A professional insulation contractor should be able to advise a homeowner about any specific requirements in your area. In some states, a professional can also provide information about available energy rebates and tax credits for home insulation projects. RetroFoam of Michigan stays up to date on current energy efficiency and insulation rebate programs and can help you determine if you are eligible for these benefits.