Thinking about insulating your basement? Ensure you know all the essential terms about basement insulation to guide your research.
Check out the 16 most important terms related to insulation in a basement.
Masonry
Your basement walls are masonry walls. Whether you have stone, block, or poured concrete, basement walls are constructed with masonry. Other building materials would not be suitable for a basement wall.
Because your basement walls are masonry, they possess some unique properties you'll have to keep in mind when choosing an insulation.
Block Foundation
You have a block foundation if your basement walls are made of cinderblocks or concrete blocks. Block foundation offers a smooth surface for insulation to be installed. Block foundation is a type of masonry, and it is porous, which means moisture can pass through it.
Poured Concrete Foundation
You have a poured concrete foundation if your basement walls are solid concrete. Poured concrete is an even smoother surface than block foundation. Even though these walls were poured as concrete, they are also porous.
Stone Foundation
If your basement walls are stone, you have a stone foundation. Stone foundations are most common in older homes and are usually paired with a dirt floor. Unlike block and poured concrete foundations, stone foundations have a bumpy surface. However, as masonry, stone also shares the same porous qualities as the other wall options.
Rim Joists
Your rim joists are where your masonry walls meet your ceiling. Rim joists are like the corner where the wall and ceiling meet. Rim joists are a vulnerable area of your basement and must be insulated properly.
As an area where materials transition, rim joists are susceptible to air leakage and vapor transfer.
Band Boards
Band boards are another term for rim joists. These terms are often used interchangeably online, including in our resources. Whether you call them rim joists or band boards, this critical basement area needs air and vapor barriers.
Vapor Retarder
A vapor retarder is a few degrees removed from a vapor barrier. Vapor retarders cannot stop vapor transfer. The rating of a vapor retarder indicates how much vapor the material will allow to permeate.
In a basement, a vapor retarder is not sufficient. Other construction applications can use vapor retarders, but basements need vapor barriers.
Vapor Barrier
A vapor barrier is vapor impermeable. Vapor is the gaseous water content in the air. Warm air holds more moisture than cold air, so as the air becomes colder, it becomes saturated with vapor.
When air cannot hold any more vapor content, the gaseous water condenses into liquid water. The purpose of a vapor barrier is to prevent vapor from entering environments where it could condense.
Basement walls and rim joists benefit from vapor barriers because these surfaces tend to be cold. A vapor barrier properly installed prevents condensation on the basement walls.
Air Barrier
An air barrier is air impermeable. Anywhere air can leak in a home can benefit from an air-seal. Air leakage contributes to poor indoor air quality, high heating and cooling bills, and discomfort in the home. Since basements face air leakage through the masonry walls and rim joists, air barriers are ideal for basement insulation.
Above-Grade
Above-grade refers to areas of a home that are above the ground. The only above-grade area that can be insulated in a basement is the basement ceiling. All other areas of the basement are considered below-grade.
Above-grade has fewer restrictions on which insulations can be installed.
Below-Grade
Below-grade refers to areas of a home that are below the ground. Your basement floor, walls, and rim joists are below-grade. Below-grade areas need vapor barriers, so their list of appropriate insulations is shorter than that of above-grade areas.
Closed Cell Spray Foam
Closed cell spray foam is a spray-applied polyurethane insulation. Manufactured on-site, closed cell offers an air barrier, vapor barrier, and a seamless application. Closed cell spray foam can be applied to any area of a basement, including:
In most applications, we install closed cell on the walls and in the rim joists of the basement. For some cellar applications, we might install closed cell on the ceiling.
Fiberglass Batt
Fiberglass batt insulation is a budget-friendly insulation option. It is available as a finished product in home improvement stores. When working with batt, it is vital to size the batts correctly to fit their installed cavity.
Fiberglass batt can be used in a basement ceiling for a few applications:
- Sound attenuation in a finished basement
- Paired with closed cell in the rim joists
Fiberglass batt is not a suitable insulation for basement walls. Some batts offer kraft paper vapor retarder facings, but fiberglass batts cannot create a vapor barrier like the ones required in below-grade areas.
Fiberglass Blanket
Fiberglass blanket insulation is a variation of fiberglass batt. These blankets of insulation are much larger, having fewer places where the insulation could be compromised.
Blanket insulation is sometimes installed on basement walls as a budget-friendly option. There are some risks when using fiberglass blankets on a basement wall.
Foam Board
Foam board insulation is a rigid foam insulation. Foam board can offer a vapor barrier when appropriately installed with seals between board edges.
Unlike spray foam, which is spray-applied and conforms to any wall type, foam board is only suitable as wall insulation for block or poured concrete foundations. The bumpiness of a stone foundation wall would make a proper vapor barrier impossible.
R-Value
R-value is the traditional measure of insulation performance. R-value stands for resistance value, and it measures how well a material resists conductive heat transfer.
As insulation materials, closed cell spray foam, fiberglass batt, fiberglass blanket, and foam board all have good R-values.
R-value does not measure how well a material resists convection or radiation heat. R-value is one aspect to remember when selecting insulation, but other factors like air barriers and vapor barriers are also important.
Ready To Insulate Your Basement?
Now you know all the important terms to understand when insulating your basement. Basement insulation is complicated by vapor transfer, air leakage, and foundation wall type.
If you're ready to insulate your basement, contact our team for a free quote. Or, learn more about basement insulation on our website, starting with these resources:
- Estimate the cost of a basement insulation upgrade
- Learn if you could spray foam your rim joists yourself
- Compare basement insulation options
Disclaimer: While we strive to publish information accurate to building science, local building codes and standards supersede our recommendations.
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