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Rim Joist Insulation Problems: 5 Things to Watch Out For

rim joist insulation

Rim Joist Insulation Problems: 5 Things to Watch Out For Blog Feature
Amanda Ringler

By: Amanda Ringler on November 30th, 2020

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Drafty basement with “that smell” getting you down?

Did you know little to no insulation in your rim joist could be responsible for several issues in your home, including that musty basement smell?

Other issues you may notice are cold floors, condensation in the basement, cold walls, and mold and mildew in the basement.

RetroFoam of Michigan has helped thousands of homeowners with their rim joist insulation problems over the past 17 years. We’ve seen it all, so we know how to make those rim joist headaches go away.

Here is a look at the top five rim joist insulation problems and how you can fix them.

Rim Joist Insulation Problems

Rim joist

From condensation issues to a drafty home, here are some of the most common problems a homeowner experiences when there is little to no insulation in their rim joist.

Moisture and Mold in the Rim Joist

Traditional insulation does nothing to prevent warm, humid interior air from getting into the rim joist.

During the winter months – when the rim joist is cold – that moisture can cause condensation, which leads to the growth of mold and wood rot.

Solution: Using a material like spray foam to insulate the rim joist will help to stop moisture from getting into the rim joist, according to Home Construction Improvement.

This is because spray foam creates an air seal, which will keep that outside cold air from meeting the warm interior air to create moisture. Another added benefit is that spray foam doesn't promote mold growth. 

Cold Spots on Walls Throughout the House

Cold air from outside can still get into your home by moving up through the rim joist.

This will make the base of the walls around your home cold and will cause drafts to come through electrical outlets and switches. This is one of the top sources of heat loss and air infiltration in the home.

This happens when there is no insulation or sagging fiberglass insulation in the rim joist.

Solution: Updating the insulation in the rim joist is one solution, but gravity will take its toll on fiberglass, especially if it gets wet as it will get weighed down. Other options include  open cell spray foam and foam board insulation.

Cold Floors Throughout the Ground Level of the Home

The cold air that is making its way into your home can lead to cold floors throughout your home.

Those cold floors are going to have your furnace working overtime. The cause is again, little to no insulation in the rim joist. You'll even probably find yourself layering socks to keep your feet warm.

Solution: Updating or adding new insulation to the rim joist will help keep those floors warmer without constantly running the furnace.

Not running the furnace as much will also save you money on your monthly energy bills.

Drafty and Cold Basement Area

Did you feel that chill run up your spine while you were getting something from your basement?

It's not a ghost, it's the outside cold air that makes its way into your rim joist. That cold air is guaranteed to make it into your basement as well.

Cold basements are uncomfortable and not the easiest to keep warm if cold air is continuously seeping in.

Solution: To keep the cold air out of your basement, you will need an insulation material that will create an air barrier.

Creating an air barrier in the rim joist will help keep the cold air out of your basement, making it a much less spine-chilling place.

Condensation in the Rim Joist and Basement

Are you experiencing that basement smell and even mold or mildew issues?

We already talked about what condensation can do in the rim joist, but did you know it can also spread to the rest of your basement? When this happens, you can smell the mildew in the air and could develop mold issues on your basement walls, as well as in the rim joist.

If you have ductwork down there, the moisture from condensation could damage it. The musty mildew smell could also travel throughout the house via those ducts, along with possible mold spores.

Solution: Condensation happens when warm air meets the rim joist's cold air and spreads to the basement.

The condensation forms and creates moisture that will cling to fiberglass. The best solution is to use an insulation material that will create an air barrier. 

Answering Your Rim Joist Insulation Problems

The key to fixing your rim joist insulation problems is understanding how the different kinds of insulation materials work.

Some homeowners have found that a better long-term solution to fix their problems has been to remove the old insulation and replace it with spray foam insulation.

If you are interested in learning more about foam insulation's benefits, check out our Learning Center.

Related Articles

What is the Best Rim Joist Insulation? (Spray Foam vs Fiberglass vs Foam Board)

How to Insulate a Rim Joist

8 Things to Do When Identifying Condensation or Mold in Your Home

Home Insulation

About Amanda Ringler

Amanda previously has worked as a breaking news and crime reporter, TV news producer, and editor in Flint and Detroit. Throughout her career as a journalist, she has won several awards from The Society of Professional Journalists - Detroit Chapter and the Michigan Press Association. As part of the RetroFoam of Michigan family, Amanda uses her experience as a journalist to write content that will help educate homeowners on the benefits of foam insulation. When Amanda isn’t writing, she’s spending time with her husband and rescued huskies. She also loves knitting, making art, cooking, and hosting dinner and a movie night for friends and family.