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Do I Need to Remove Old Insulation Before Installing New Spray Foam?

By: Malcolm Bean on May 18th, 2020

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Do I Need to Remove Old Insulation Before Installing New Spray Foam?

Featured  |  retrofit  |  FAQ  |  Foam Insulation  |  insulation  |  remove old insulation

The saying goes “out with the old and in with the new” and it’s true when installing foam insulation in your home.

You have done your research and have decided on foam insulation for your home because of the material’s ability to create an air seal that greatly improves comfort and reduces monthly energy bills. There’s only one more thing to figure out – do you need to remove the old insulation before installing the new?

RetroFoam of Michigan has more than 17 years of experience insulating thousands of homes across the Mitten, so we can help answer this question for you.

In our continued efforts to educate homeowners, we’ll explain when that old insulation needs to go and when it can stay right where it is.

Can You Spray Foam Over Existing Insulation?

cellulose home insulation

Like many things in life, different situations will have different solutions. 

For example, the way the foam insulation is installed and the cleanup necessary in an attic is vastly different than in the walls.

Any space that will have spray foam insulation installed, like the attic, crawl space, rim joist or open walls during a remodel will need to be completely emptied of the old insulation. A good contractor will want to remove that old fiberglass or cellulose so the spray foam can get into every nook and cranny, creating an air barrier.

Luckily, getting the old traditional insulation out of the attic, crawl space, and rim joist is only hard if you have to do it yourself. But why does it need to be removed and doesn’t it just add extra insulation?

No, it doesn’t. Honestly, the old insulation is just in the way. Spray foam insulation needs a clean space to adhere to, and when insulating the roof deck, you want that air circulation as you just made your attic a conditioned space.

Most contractors will take care of the dirty work for you. A crew will come to your home and vacuum the old insulation up if it’s blown-in or carry out the fiberglass batts. They will also dispose of the old insulation material, so you don’t have to.

When it comes to installing injection foam in existing walls, the foam will flow through the cavity and compress the fiberglass. However, if there is cellulose in the walls, that can keep the injection foam from filling the cavity like it is supposed to.

A good contractor will remove the bottom row of siding before the injection foam installation, drill holes, and vacuum out the cellulose.

Health Benefits of Removing Old Insulation

Another good reason to remove that old, ineffective insulation in your home has everything to do with keeping your family healthy.

Fiberglass and cellulose are known to retain allergens, as well as moisture that leads to the growth of mold. These issues can lead to health problems, which is something you want to avoid. 

Old insulation also runs the risk of becoming a critter condo if rodents get into your home. These rodents can bring a number of diseases with them, so it’s best not to leave that old insulation in place as an invitation to them.

Creating a Healthy, Comfortable, and Energy Efficient Home

Now that you have a better understanding of why that old insulation needs to be removed, it’s time to get started to creating the healthy, comfortable home you’ve always dreamed of.

That old insulation in the attic, crawl space, and rim joist isn’t doing you any favors and actually hinders the installation of your new spray foam insulation. Plus, that old insulation in those areas is gross and could lead to allergy flareups or worse in the future.

If you’d like to learn even more about the installation process, check out our Learning Center.

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