Do Rim Joists Need To Be Insulated?

If you've found this article, you have rim joists in your basement lacking insulation. You're probably experiencing cold floors and high energy bills in summer and winter. Regardless, you're wondering if the rim joists in your basement need to be insulated.

South Central Services has insulated hundreds of new and existing homes around Chambersburg, PA with spray foam insulation. Rim joists, also known as band boards, often have ineffective insulation or no insulation at all. The question isn't whether band boards need insulation but rather how they should be insulated.

By the end of this article, you will know:

• Why rim joists are often poorly insulated
• Why rim joists are difficult to insulate
• If you should invest in rim joist insulation

Don't have time to read right now? Check out everything you need to know at a glance.

Rim Joist Insulation Is Required By Building Codes.

One reason rim joists often lack effective insulation is building codes. For a basement to meet building codes, either the basement ceiling or basement walls must be insulated. The rim joist is where your ceiling and walls meet, so rim joists are also insulated as extensions of the ceiling or the walls.

Depending on the age of your home, there may not even be insulation to meet building codes. However, when new homes are built, their basements are commonly insulated to meet the bare minimum requirements. Builders will not go above and beyond what is required by building codes.

This means that fiberglass batt insulation is the most common insulation in rim joists. The presence of batt insulation meets the building code, even if it is ineffective in that application.

Rim Joists Are A High Infiltration Point For Cold Air.

So, why are rim joists more vulnerable to cold infiltration than other areas of your home?

A rim joist is where a masonry wall transitions to a wood frame. Your masonry basement walls lay beneath the wood beams that support your floors. While masonry and wood are both building materials, they have very different properties.

A simple example of their differences is porosity. Wood is not an especially porous material, but masonry is quite porous.

Cold air can travel through your basement walls and easily push through your floors at this rim joist location.

Rim Joists Are Notoriously Difficult To Insulate.

Despite their influence on energy efficiency and comfort in the home, basement band boards are rarely insulated effectively. Why do home builders opt for batt insulation that cannot perform? Rim joists are often given the bare minimum because it is difficult to insulate them.

Basement band boards are awkward spaces. Getting a traditional insulation product into the rim joists effectively is difficult.

The most popular insulating material, fiberglass, is often stuffed into the rim joist. Unfortunately, attempting to make fiberglass batts in the band boards effective would be time-consuming and still less effective than an airtight seal.

You would have to cut the batt insulation to the size of each rim joist cavity. Additionally, fiberglass insulation functions by allowing air to pass through it. After all that work, even without any gaps or cracks, cold air could still infiltrate your home from the band boards.

Another insulation sometimes used in basements is foam board insulation. If paired with can foam, foam board could create an airtight seal. However, just like with fiberglass, foam board insulation must be cut to size.

With the numerous plumbing and electrical protrusions that can exist in your rim joists, sizing all of that foam board would take forever. Even if you had the patience, you would inevitably have countless seams in your insulation that would need to be sealed with caulking or can foam.

Rim Joists Should Be Insulated With Closed Cell Spray Foam.

What is the solution for an area of the home that is difficult to insulate and needs an airtight seal? The answer is closed cell spray foam.

Closed cell spray foam is a dense, spray-applied insulation that creates an airtight seal. All of the awkward angles of basement band boards do not matter with closed cell spray foam. Any contour in your rim joists can be addressed with an insulation that adheres where it is sprayed.

Closed cell spray foam can also create a vapor barrier at two inches of depth, preventing condensation issues. Most importantly, spray foam's airtight seal prevents cold air from infiltrating your rim joists.

Rim Joist Insulation Will Make Your Home More Comfortable.

Basement rim joists do not need effective insulation to pass building codes. However, you should consider spray foam band board insulation for the comfort of your home.

If you are experiencing cold floors upstairs, band board insulation will make your floors warmer. If your home is colder in the winter and hotter in the summer, band board insulation can help regulate your indoor temperature. Stopping air infiltration is critical to supporting your thermostat and HVAC system.

The Bottom Line About Why Rim Joists Should Have Insulation

Home construction is fascinating. Somehow, many construction disciplines come together to create a functional house. You may not think of your basement rim joists as a problem area in your home. It can be hard to believe the impact that an airtight seal in the band boards can have.

Ineffective rim joist insulation is enough to meet building codes. However, you should insulate this area of your home for your own comfort and energy costs. Using closed cell spray foam insulation for your rim joists would be best. It creates a seamless air and vapor barrier to stop cold air infiltration.

Now that you know why you should invest in spray foam insulation for your rim joists, your next step is to:

• Discover which insulation products are best for your basement walls
• Learn about the benefits of insulating rim joists with spray foam
• Find out how much spray foam in your rim joists will cost