Basement Insulation
Madison, WI

Basement Insulation


Insulation basement projects commonly get skipped or just use fiberglass batts. Unfortunately, there’s major problems with both scenarios.

Both cellulose and spray foam insulation on the basement walls will keep the area comfortable and safe all year round. Which is the most efficient and effective choice depends on the situation.

Moisture is the Problem

Concrete foundation wall insulation is exposed to far more moisture than in other areas of the home, and fiberglass is irrevocably damaged by moisture. This means what insulation insulation quality there was degrades quickly. Since uninsulated basements get too cold in the winter, finished basements tend to be rarely used and are prone to mold. 

The Best Basement Insulation

Most Effective: Blown in cellulose (R14) for basement wall insulation and spray foam (R21) for box sill insulation
Notes and Exceptions
A great deal of moisture passes through cement foundation walls. This can cause mold growth inside walls if not managed deliberately. Fiberglass permanently loses insulation value after becoming wet, but cellulose handles moisture extremely well.
Box sills are one of the (air) leakiest parts of the home. Insulating this area is equally important as any other exterior wall, but air sealing it is critical.

The Most Recommended Option

For Basement Walls and Box Sills

Walls: Cellulose costs less than fiberglass when factoring in heating bills and manages moisture far better.

Box Sills: The key here is air sealing, and spray foam insulation also air seals exceptionally well.

Basement Wall Insulation

Similar to Other Walls
Basement walls are highly similar to exterior walls aside from one primary distinction: A considerable amount of moisture passes through concrete foundations. This changes vapor barrier protocols and makes moisture-sensitive fiberglass a particularly bad choice. Otherwise, check out the walls article for more info.

Not insulating basement walls in northern climates typically results in not using the basement for half the year.

Basement Ceiling Insulation

Sound and Floor Warmth

The 2 most common reasons home owners insulate basement ceilings is for sound control and to warm up the floor above. Depending on furnace vent location, this may cause the basement to grow colder. Insulating basement walls will warm both the basement and floor above.

More on Box Sills

Because it’s a pain caulk and hand-pack insulation into each sill, the construction industry has quickly shifted to spray foaming these areas.

Having box sills spray foamed is often the biggest “bang for the buck” of any air sealing and insulation improvement. This is because they’re small, generally easy to access, and a perfect target for spray foam. Since the area is relatively limited, the material cost of spray foam doesn’t drive up the project cost as it normally would.

Box Sills

Critical Air Sealing Area

The gaps above the basement walls between the boards holding up the floor above are called box sills. You can see them in any unfinished (un-drywalled) basement. They are by far the leakiest part of most homes, and together equate to a year-round open window in the basement.

Types of Insulation

A Big Difference

No matter the location, insulation type plays a big role in results. We go into detail about the 3 common insulation types in this article.

Insulation Types at a Glance

Fiberglass is the least expensive upfront, the least effective, and the most expensive over time.

Cellulose is slightly more expensive upfront, a great insulator, and offers by far the biggest “bang for your buck.”

Close cell spray foam (polyurethane 2-part foam) is the most expensive, offers unmatched insulation value, and generally gets the job done when other insulations won’t.

Crawlspace Insulation

Most Effective: Spray foam walls (R21)
Why Walls?
The short answer is it’s cheaper, safer, and equally effective. Because these areas are so short, there is often less square footage to cover on the walls than the ceiling (or underside of the floor above). There also needs to be a vapor barrier either over the dirt “floor” or over the ceiling. By insulating the walls, the barrier (a sheet of plastic) can be across the floor so it can’t fall down after a few years. Finally, this option creates a contained semi-heated area so outside air can’t sneak into the attached basement or up through the walls.
Why Spray Foam?
Spray foam sticks to surfaces, so there’s no need to build a retaining wall to hold the insulation in. It also can be used on the crawlspace ceiling (if that is a better option) and removes the need for the vapor barrier that could fall down (spray foam is a vapor barrier and never falls off). Finally, it is immune to moisture damage, and crawl spaces are notoriously humid.
Why R21?
Diminishing returns. It’s the sweet where most of the heat transfer is prevented without running up the project costs. See exterior walls for more details.

Crawlspace Insulation

A Single Best Solution

Most people insulate crawlspaces to warm the floor above them. While insulating that floor seems obvious, it’s almost always better to insulate the crawlspace walls instead. It’s less expensive and equally effective.


State Rebates & Incentives

Many (though not all) Wisconsin insulation projects are eligible for hundreds of dollars in rebates through the state’s Department of Energy. We typically are able to help at least one client capture a rebate each week.

We are certified to implement these rebates and complete nearly all the paperwork for you. We even instantly discount the rebate from your invoice, so you’re not left waiting for the rebate check to arrive.

Know YOUR Numbers

Planning with general numbers often leads to inaccurate estimations and budgets. That’s one of the many reasons we offer free estimates. Whether you need a quick fix or are planning for work next year, work with actual numbers specific to you.