Benefits Of Rim Joist Spray Foam

You've heard you should get spray foam for your basement rim joists. But why do you need new insulation there? Is the insulation in your rim joists already not enough? Why should you invest money in an expensive product like spray foam for such a small area of your home?

South Central Services has insulated hundreds of new and existing homes with spray foam. Despite forming such a small portion of your thermal envelope, your rim joists can greatly impact your energy costs and home comfort.

By the end of this article, you will understand:

• Why your existing rim joist insulation isn’t enough
• What spray foam offers that your existing insulation doesn’t
• How spray foam in your rim joists benefits your whole home

Fiberglass In Your Basement Band Boards Isn’t Enough.

Most basements in southern Pennsylvania have fiberglass batt insulation stuffed into the rim joists if they have any insulation at all. Fiberglass has become standard for homebuilders. Since rim joists need to be insulated, the presence of fiberglass insulation passes building codes.

Unfortunately, fiberglass insulation is not suitable for basement band boards. The fiberglass batts insulate by allowing air to pass through. As air travels through the fiberglass, heat transfer is slowed. Air easily infiltrates areas where fiberglass is installed, especially if there are any gaps in the insulation.

This air infiltration is undesirable for your basement band boards. The rim joist of a basement is where a masonry basement wall meets the wood floor joists of the first floor. The transition from porous masonry to treated, non-porous wood creates an area for cold air to infiltrate.

Fiberglass cannot stop this cold air. Instead, the air freely exchanges with the air inside, which you pay to keep at a conditioned temperature.

Spray Foam In Your Rim Joists Creates An Airtight Seal.

You can install an airtight seal in your rim joists by replacing fiberglass insulation with spray foam. With an airtight seal, no cold air within the masonry wall can escape through the gap created by your band boards.

Both types of spray foam insulation, open cell and closed cell, can create an airtight seal. For closed cell foam, approximately 1 inch of insulation is enough. Open cell foam needs approximately 3.5 inches to create an airtight seal.

Since your band boards are exposed to air and vapor, closed cell spray foam is the insulation of choice. At 2 inches, closed cell can offer both an air and vapor barrier.

What Are The Benefits Of An Airtight Seal In Your Rim Joists?

Spray foam insulation creates an airtight seal, and fiberglass insulation cannot. But what does that practically mean for you as a homeowner?

There are four benefits of an airtight seal in your basement band boards. Here's a preview.

1. Fewer pests
2. Warmer floors
3. Longer-lasting HVAC equipment
4. Lower energy bills

Let’s examine each of these benefits in more detail.

1. An Airtight Seal Mitigates Insect And Pest Infiltration.

No insulation is pest-proof, not even spray foam. At best, insulation is part of a multi-tiered pest-control strategy. In the case of your basement band boards, spray foam's airtight seal helps to mitigate insect infiltration.

The gaps in your rim joists are pathways for spiders and other common basement insects. By sealing up those gaps with spray foam, pests have to find different avenues into your basement and home.

2. An Airtight Seal Makes Your Floors Warmer In The Winter.

For homeowners in southern PA, the weather varies by season. Our summers are hot and muggy, and our winters have the occasional snowstorm and slushy roads.

Without an airtight seal in your rim joists, cold winter air leaks into your home. Your floors are cold. You crank the heat. No amount of blankets seems like quite enough.

An airtight seal in your band boards significantly affects your home's comfort during winter. In our climate zone, homeowners notice a huge improvement in the wintertime comfort of their home.

3. An Airtight Seal Supports Your HVAC System.

This benefit may feel like a bit of a stretch. How can insulation help your HVAC system?

There is a close relationship between insulation and HVAC. An airtight seal that keeps out cold air benefits your HVAC system in two ways.

By keeping cold air outside your home, your HVAC system has fewer air leaks to combat. Every time air exchanges uncontrollably from your home, the air that leaves is conditioned, and the air that enters is the same temperature as outside. Every air leak you can prevent helps your HVAC system run smoothly rather than playing catch-up to changing indoor temperatures.

Additionally, with fewer cold air leaks, you will likely not run your heat at as high of a temperature. Before the airtight seal, you may have needed to crank your heat higher to balance out the cold in your floors or the chill in the air. After installing an airtight seal, your home can feel comfortable even without raising the temperature on your thermostat as high.

Both of these help preserve your HVAC equipment. Since the machines do not have to kick on and run constantly or run at a higher temperature, an airtight seal should support your HVAC and help it last longer.

4. An Airtight Seal Helps Lower Your Energy Bills.

Less cold air does mean a more comfortable home in the winter and less wear and tear on your HVAC system. However, less cold air also directly relates to the cost of heating your home.

In the winter, every degree of difference between the outside and your thermostat is increasingly expensive. The natural result of an airtight seal making your home less cold means you won't have to try to make it hotter.

Spray foam in the basement band boards will lower your energy bills, especially during the peak pricing of the winter.

An Added Bonus: Rim Joist Spray Foam Has A Fast ROI.

One additional benefit of insulating your rim joists with spray foam is a fast return on investment. Hiring professional contractors to install spray foam in your rim joists could cost anywhere between $1,500 and $4,000.

As far as spray foam insulation upgrades are concerned, this is a relatively low investment cost. Projects like insulating your attic or encapsulating your crawl space have a higher price tag.

Since the cost of spray foam in the basement band boards is relatively low, it pays for itself quite quickly. Despite being a small area of your basement, rim joists contribute a lot of cold air infiltration. Cutting off that cold air with an airtight seal makes a big difference in your energy costs.

Depending on your home's insulation and when you insulate the band boards, this spray foam investment could pay for itself within 2 to 5 years.

The Bottom Line About The Benefits Of Spray Foam In Rim Joists

Spray foam insulation outperforms fiberglass in most areas. Spray foam offers a higher R-value, creates an air barrier, and closed cell spray foam can also create a vapor barrier. By installing closed cell spray foam in your rim joists, your home can benefit from an airtight seal.

Preventing cold air infiltration lowers energy costs, supports your HVAC system, and makes your home more comfortable to live in during the winter. Sealing up these gaps even deters spiders and other insects from living in your basement.

If you have cold floors during the winter or high energy bills, consider contacting a qualified contractor about installing spray foam in your band boards.

Now that you understand the benefits of spray foam in rim joists, your next step is to:

• Discover whether DIY spray foam is an option for your rim joists
• Learn how to insulate your concrete basement walls
• Determine where else in your basement may need insulation