Should You DIY Spray Foam Your Rim Joists?

If your floors are cold in the winter, your basement rim joists are likely to blame. Without an airtight seal, rim joists allow the cold air outside to infiltrate your home. Spray foam insulation can deliver the airtight seal that your rim joists need. But should you install the spray foam insulation yourself?

South Central Services has insulated hundreds of new and existing homes with spray foam. We only recommend DIY spray foam for small projects, which rim joists often qualify as. However, DIY spray foam always comes with risks, which you should be aware of before you begin.

By the end of this article, you will know:

• When to consider DIY spray foam for basement rim joists
• What additional purchases to make when using DIY spray foam
• If you can save money by insulating the rim joists yourself

Are Rim Joists A Good Option For DIY Spray Foam?

There are lots of reasons why people gravitate towards DIY projects. Some people are price-conscious and look for any way to save money. Others are creative and enjoy making things with their own hands. Still more people love to gain new skills, and DIY activities give them the opportunity to learn.

DIY spray foam insulation is not a project we recommend for a variety of reasons. In almost every case, installing spray foam yourself will not save money. Additionally, because spray foam is created through a chemical reaction, DIY spray foam can be dangerous and difficult to install safely.

We have seen many DIY spray foam failures where these kits delivered a failed product that was difficult to clean up and replace.

It is tempting to think that the small size of a basement rim joist job eliminates the risks of DIY spray foam. However, risk is not mitigated by size. Any amount of foam can fail.

Our recommendation is to work with a qualified professional spray foam contractor. In most cases, hiring a professional will not cost significantly more than using a DIY spray foam kit. By hiring a skilled professional, you completely mitigate the risk of failed foam.

Insulating basement band boards with spray foam costs between $1,300 and $3,000 for a standard home. This cost includes prep, installation, clean-up, and the assurance that if your contractor did make a mistake, your insulation is covered by insurance.

Attempting to install spray foam as a DIY may not cost $1,300. However, you will be responsible for everything, including the possibility of a failed foam that must be removed.

What You Need To Purchase To Install DIY Spray Foam

If you are not dissuaded by the risks of installing spray foam yourself, you will need to purchase several things.

1. DIY spray foam kits
2. Manufacturer recommended PPE
3. Plastic sheathing

Let’s examine these purchases in more detail.

1. Purchase Enough DIY Kits To Cover Your Project’s Board Feet

Obviously, you will need to purchase DIY spray foam to install the insulation yourself.

It is important to purchase enough to cover the board feet of your basement rim joists. This may be a single DIY kit, or it could be multiple. DIY kits list their expected yield by board feet, but it is uncommon for a spray foam kit to meet that yield. Always assume your DIY kits will deliver less finished product than promised.

The spray foam chemical reaction performs best with heat. See the manufacturer's directions for the optimal operating temperature of that material.

The three key variables of the spray foam chemical reaction are temperature, pressure, and ratio. At best, you can attempt to monitor the temperature of your material according to the manufacturer's directions. Cold spray foam components will be ineffective and deliver poor yield. However, it is also possible to overheat or burn spray foam. Do not store your DIY kit in your cold basement, even though you plan to insulate in your basement.

As for the other variables in the chemical reaction, you can do nothing with your DIY kit to keep your material on-ratio or maintain the pressure you spray at.

When you hire a professional, these variables are all carefully monitored and controlled in their spray foam rig. The necessary equipment is expensive, and DIY kits cannot offer anything comparable.

DIY spray foam kits generally cost between $1.80 and $2.20 per board foot, assuming a perfect yield.

2. Purchase Appropriate PPE, Per The Kit Manufacturer

Professional contractors wear a lot of personal protective equipment (PPE) to protect themselves while spraying. Since spray foam is created through a chemical reaction, the overspray and off-gassing of that reaction require protection for the eyes, lungs, hair, and skin.

Despite PPE being nonnegotiable for installing spray foam insulation, DIY spray foam kits do not include any PPE. At a bare minimum, you must protect your lungs with a respirator and your eyes with safety glasses.

You should contact the manufacturer of your DIY kit to find out what type of respirator you should use when installing their foam product.

You may also want to purchase disposable coveralls to protect your clothes and skin from overspray. Since spray foam adheres to the surface it lands on, removing overspray droplets from clothes is nearly impossible.

The appropriate respirator and coveralls could cost anywhere from $70 to $100.

3. Purchase Covers For Your Belongings And Other Surfaces

When you hire a professional, they are responsible for prepping the workspace and protecting anything that overspray could hit. By installing spray foam yourself, you take on that prep work.

Depending on where you live and the hobbies you enjoy, you may or may not have plastic sheathing, tarps, and tape on hand. If you don't already have these materials in a workshop, you must invest in covers for your basement belongings.

Even if there are not any belongings you feel compelled to cover, you want to cover any surface you don't want overspray stuck to.

The thickness of your plastic covers and the quality of your tape will determine how much you may spend. However, acquiring these prep materials could easily cost between $60 and $120.

Can You Save Money By Insulating Your Rim Joists Yourself?

If your projected DIY costs are less than $1,300, you may save some money compared to hiring a professional. However, you also incur significantly more risk. DIY spray foam has a high track record of failure.

Saving a few hundred dollars may seem insignificant if the foam you spray fails.

The Bottom Line About Spraying Foam For Rim Joists Yourself

Despite the small size of basement rim joist projects, we recommend working with a professional spray foam contractor. While there are steps you can take to help mitigate the risk of DIY spray foam, the risk cannot be eliminated. DIY spray foam cannot monitor or control the chemical reaction it creates. The wrong temperature, ratio, or pressure results in a ruined finished product.

Failed DIY foam creates a headache for homeowners wanting to save money or learn a new skill. After paying for removal and replacement, no money is saved.

Now that you understand how much it will cost to install rim joist spray foam yourself, your next step is to:

• Learn what drives up the cost of professional rim joist spray foam
• Discover the benefits of an effective and airtight seal in your rim joists
• Find out why homeowners trust South Central Services to insulate their basements