All You Need to Know About Insulating Your Basement Walls

All You Need to Know About Insulating Your Basement Walls

By Dikran Seferian April 19, 2022

It goes without saying that insulation can turn a neglected basement into a comfortable living space. Whether you’re planning on transforming your basement into a fitness room, a home theater, or a play zone for your kids, insulation can really make it possible. However, this doesn’t mean going for just about any insulating material you can find on the market. It’s important to bear in mind that basements are naturally damp environments, and only certain types of insulation can be suitable. These typically include rigid foam boards, spray foam, as well as mineral wool sheets. Not only will insulating your crawling space turn it into a habitable and functional area, but it can also considerably enhance the comfort of the rooms above. 

Why Is It Important to Insulate Your Basement Walls?

Having your basement walls insulated is important and beneficial for several good reasons. These include conserving energy, cutting expenses, and boosting comfort. In certain regions, basement wall insulation is even required by law. In any case, it should be considered a priority for homeowners — and a handful of reasons explain why.

Energy Efficiency

It is commonly believed that insulating either the basement floor or the ceiling should be enough. However, it actually isn’t a very effective way to keep the space insulated. It may come as a surprise that a basement is connected to living spaces in more ways than one might assume.

Much of the indoor air around you that you breathe every day actually makes its way to the main floor from the basement. Naturally, that air carries the temperatures you’d find in the basement, and since that space is mostly underground, it’s normally cooler than other rooms in the house. Adding insulation to the basement walls effectively guards your living spaces against the underground cold. This allows your HVAC to run more efficiently, thereby reducing your energy usage.

Cutting Costs

Insulating your basement can be cost-efficient in the long run by driving your energy bills down.

Insulating your basement can be cost-efficient in the long run by driving your energy bills down.

As your energy usage decreases, your utility costs will naturally follow suit. Covering the foundation walls with basement insulation will allow your HVAC to require less maintenance, incur fewer expenses, and ultimately last longer. 

Enhanced Comfort

Properly insulating your basement walls will not only allow your HVAC to run more efficiently but will also enhance the comfort levels of your home. This means you won’t need to worry about sudden temperature drops in the winter, having to wear extra socks around the house, or having to crank up the heat to stay warm (which would otherwise lead to high energy bills).

Code Requirements

There are several requirements in regards to the health and safety of the family members when it comes to finishing a basement. Insulating the basement walls is among these codes. Also, in the case of an already waterproofed basement, insulating its walls is usually the first step of the finishing project. 

Insulating Your Basement With Rigid Foam Boards

Rigid foam boards ensure seamless insulation.

Rigid foam boards ensure seamless insulation.

Rigid foam insulation basically consists of large boards of expanded polystyrene foam. You can find them in most home centers and you can find them in sizes up to 4 feet by 8 feet. They’re usually ½ to 2 inches thick with R-values ranging from R-2 to R-10. In most cases, the boards are vertically scored, allowing you to snap the sections off instead of having to cut them.

You can install the foam boards either vertically or horizontally. Make sure the boards are as large as possible to allow for seamless insulation. Consider making use of low-expanding spray foam to fill any gaps and holes. 

When to Use Rigid Foam Boards

Rigid foam boards can be ideal if you are planning to insulate your basement before framing its walls. This method of insulation is also best in the case of concrete walls that are flat and smooth. It is generally easy to install, and can even be done as a DIY project. Besides scoring, you can also cut the boards using a regular wood saw.

Covering 32 square feet of walls with foam board insulation of an inch thick will normally cost between $20 and $30. This makes rigid foam sheets an excellent choice if you’re on a budget.

Insulating Your Basement With Spray Foam

There are many convenient insulation methods for your basement walls, one of them being spray foam.

There are many convenient insulation methods for your basement walls, one of them being spray foam.

Arguably the best way to insulate basement walls, spray foam is applied to the cavities between the studs of the basement walls using a kind of gun. The polyurethane foam begins to expand upon contact with the surface. Once dried, any excess foam can be trimmed off. Although DIY kits are available, spray foam insulation is best done by professionals.

Spray foam insulation is available in two different forms: open-cell and closed-cell. Both of these can effectively insulate your basement walls while blocking the flow of air. Open-cell foam, in particular, is known to expand up to 100 times in size, allowing it to fill up every cavity in the wall.

Unlike many other insulation materials, spray foam doesn’t sag, settle, or lose its form over time. Besides filling nooks and crannies as well as preventing airflow, it can also provide structural support.

When to Use Spray Foam Insulation

Spray foam insulation is the ideal choice when the basement wall studs are already in place. Consider using spray foam when you need the insulation process to be continuous in order to prevent air infiltration. It is a go-to option for basement walls that are irregular or those with joints, cracks, and seams. 

Insulating Your Basement With Mineral Wool

Mineral wool is an eco-friendly insulation material you can use.

Mineral wool is an eco-friendly insulation material you can use.

Also referred to as Rockwool, mineral wool is an insulation material produced by spinning stone or silica under intense heat and pressure. The end result is a soft and fibrous sheet that resembles fiberglass batts. Mineral wool sheets, however, are then pressed into dense mats that function like rigid foam boards. This material is also known to be moisture resistant, making it a great choice for humid environments such as basements.

You can normally use a saw or a kitchen knife to cut the mineral wool sheets into sections. It’s always best to install the sheets in large sections, just as you would with rigid foam boards. 

When to Use Mineral Wool Sheets

Mineral wool can be a great alternative if you prefer not to use plastic varieties like rigid or spray foam. The material used in this type of insulation is completely natural as it purely consists of recycled substances. Mineral wool boasts a melting point of 2,150 degrees Fahrenheit, making it practically fireproof under normal circumstances — as opposed to the low melting point of rigid foam. As for R-value, mineral wool sheets with a thickness of an inch and a half have a rating of R-6.

You can expect to pay up to $100 for 32 square feet of mineral wool insulation. This makes it around three to five times more costly than having your basement insulated with rigid foam boards.

Some materials are not suitable for basement insulation.

Some materials are not suitable for basement insulation.

How Not to Insulate Your Basement Walls

Insulation methods that you’d normally use for upper floor walls may not be ideal for your basement. These include fiberglass batts, blown-in cellulose, and denim insulation. Such materials are known to be permeable and can absorb moisture rather quickly. They are also known to develop mold and mildew in humid conditions. This can cause the wooden studs and the plates to rot. Moreover, the moisture and the mold can eventually make their way to the back of the drywall.

That being said, you may want to make sure there is no water leakage in the basement before getting any insulation work done. Guaranteeing that the space is completely dry can prevent you from having a lousy experience with the project — and can save you a great deal of money that would otherwise go to waste.


Written by
Dikran Seferian

Written by Dikran Seferian