Insulation is an important aspect of home design especially when you live in a cold winter environment and use a furnace or other heating option in the winter. Significant heat loss occurs in a home for a number of reasons and the basement is one of the worst culprits which is why insulation is so important.
R value is an additive measurement of the thermal resistance to heat flow so the higher the R value the better the insulation. A minimum R value of R-11 is suggested for the basement unless you live in a cold winter environment in which case a value of up to R-25 is more suitable to prevent heat loss.
Let’s talk more about R value, insulation options and what makes the most sense for your basement.
What R Value Insulation Do I Need For Basement Walls?
The higher the R value, the better it is able to retain heat in your home and reduce your heating costs while also making your basement more comfortable. R value is also additive so if you had insulation for example rated at R-10 and added another layer of insulation of R-5 the total value becomes R-15.
Depending on where you live in the US
and the severity of winters you get, your basement wall R value requirements – often stipulated by your local building code – will differ. Click here if you live in Canada to search by city and province.
In general terms:
- The south up to about Kansas and North Carolina is generally R 11 up to R 25 slightly farther north.
- The north where snowy, icy and cold winters are the norm will require R 25.
Why do we insulate our basement walls?
The main reasons for insulating the basement include:
- To improve overall energy efficiency of the home. Wood-framed homes especially have very cold basements in winter in part because basements are built underground and because wood and concrete have low R value on their own.
- To keep basements comfortable for using in winter. Basements are often built with minimal heating and usually add a fireplace or space heaters to heat them in winter. Insulation helps to retain heat and make basements more usable and comfortable in winter especially when we heat the basements for use.
- To reduce dampness. Basements can get damp, musty and wet in extreme cases. Insulating your basement adds a vapor barrier to reduce the chance that moisture gets into the living area to additionally make the basement more comfortable to use in winter.
Do you need to insulate basement walls below grade?
Below grade is a term used in real estate and home building that refers to building below ground. Typically this refers to a basement or cellar. When you build below grade, the insulation requirements are higher than above ground floors like the main (first) floor of a home or the second floor excluding the attic. It gets colder underground than above ground and heating in a basement might be limited compared to upstairs.
Often in unfinished basements and older houses there are just enough heating vents to keep the equipment (water heater, furnace, water pipes) from freezing and heat is often supplied to the basement on demand with a fireplace when you are actually in the basement to make it warm enough for human use.
Given that basements are built below grade, they can get damp and moist especially during winter and more so if there are water leaks. Certain types of insulation such as fiberglass can’t be applied directly against concrete because when it gets moist, fiberglass can develop mold which ruins it and will eventually result in the need for replacement.
That’s why you will see rolls of fiberglass (called a batt) covered with thick clear plastic on either side and secured in place with tape like the pictures on this page. So you get the benefit from the fiberglass but the plastic is a vapor barrier to protect the fiberglass against moisture.
What type of insulation is best for basement walls?
Basements are generally insulated with several types of insulation.
Fiberglass insulation
As shown in many of the pictures on this page, the easily recognizable pink batt (rolled) insulation is placed on walls in between wooden frames to hold them in place. Fiberglass batt insulation has been long used to insulate walls through homes on each floor. It has traditionally been used due to its relatively low price, its good R value when applied liberally, wide availability and its usability in various part of your house.
The only place it wasn’t really used is in the attic which traditionally sees blown-in insulation utilized as it is quicker and easier to apply with a large hose. Most houses have fiberglass insulation especially older ones.
Rigid foam insulation
Rigid foam insulation is also known by other names like insulating boards and continuous insulation. It offers higher R value than figerglass similar R value of spray foam which we’ll discuss below. To comply with building codes, a clear plastic vapor barrier is then added over top. Rigid foam is very resistant to moisture and as such is often used on exterior foundation walls.
Rigid foam often leaves small gaps that should be filled in with low-expanding spray foam sealant to close them up to prevent heat loss.
Spray foam insulation
Spray foam insulation is the most expensive form of home insulation but for an increasing number of people and builders it’s also the most effective. Spray foam acts as both an insulator and vapor barrier and also has sound dampening benefits. While spray foam can be installed as a do-it-yourself project, you should pay a pro to do it properly to get the full benefits. The vapor of spray foam can be flammable and installing it properly does take skill.
The installation process will be messier than the other two options since you are spraying a material with vapor into your home. It’s also more costly up front.
Summary
Moving forward spray foam insulation will undoubtedly become more widely used and accepted and more cost effective. The payoff period for spray foam insulation might be 2-4 years currently but it is for many people the best insulation choice for their homes.
The benefits spray foam offers includes the fact that it’s waterproof, adds soundproofing and works very well in cold environments. It’s also permanent and won’t need to be replaced unlike moldy fiberglass.
At this point in time the extra cost is the only downside to spray foam insulation but this should be less of a concern over time as more competitors enter the market. In that regard, consider spray foam for your basement walls and compare with other options available to you before making a decision.
Fiberglass vs rigid foam vs spray foam basement insulation
Traditional fiberglass insulation batts, rigid foam insulation and spray foam insulation each provides several similar benefits. They each:
- Offer consistent R value when installed correctly for heat retention.
- Are both able to meet local building code requirements for minimum R value protection.
- Produce no known harmful emissions after installation. Spray foam does have a vapor when being installed however.
But each option differs in several ways as we’ll discuss below:
| Fiberglass | Rigid | Spray foam | |
| Cost | Cheaper to buy and install. Expect to pay $0.90 – $1.75 per square foot installed. | Medium priced. Expect to pay Expect to pay $1.65 – $2.75 per square foot installed. | Most expensive to buy and install. Expect to pay $2.00 – $6.75 per square foot installed. |
| R value per inch | Lowest. You need more fiberglass insulation to achieve similar R values to what rigid or spray foam offers. | Higher R value than fiberglass and similar to spray foam. | Higher R value than fiberglass and similar to rigid foam. |
| Uses | Anywhere in the house except the attic which uses blown insulation for ease of application. | Anywhere in the house including internal and external walls. Used on external foundation walls. | Anywhere in the house including internal and external walls. |
| Installation | More difficult to install with more work and waste produced. Must be cut to fit the area being insulated. | Easier to use, easy to cut and fits throughout the home. Does leave gaps which should be filled with spray foam sealant. | Easily applies over curved and irregular surfaces with less work and waste produced. |
| DIY | You normally need a pro to install fiberglass properly and in a new home, it’ll be done by the builder. | Yes. If you’re handy you can do this work yourself but may want to pay a pro to do it right. | No. While many people do and you can buy spray foam at retail, it should be applied by a pro and can constitute a fire hazard during installation due to the vapor. |
| Benefits | Cheapest option with a long track record of usage. | Compact, green and needs no maintenance as it’s very tough ie. rigid. | Permanent once applied. Tightly seals gaps and holes. Further acts as a sound barrier of sorts. |
| Waterproof | No. Must use plastic vapor barrier and if fiberglass gets wet, mold will set in which can become a health hazard. | Yes and can thus be used to insulate the exterior of a foundation. | Yes. Spray foam is not damaged by water. Can be applied directly to concrete walls, too. |
How much insulation does a basement need?
So, what R value insulation do I need for basement walls? How much total insulation do I need?
As mentioned above, there are a number of factors that determine how much insulation you require including where you live. The harsher and colder your winter, the more insulation you will require. The following is also important:
- The age of the house. The older the home, the less energy efficient and more insulation you may require as it was undoubtedly built with less insulation than is required today.
- The size of the home. Obviously the bigger the home the more insulation you require.
- Whether or not you have a basement or attic. The attic can be responsible for up to 25% of heat loss in a home and another 15% through the floors and basement.
- Whether or not you have a fireplace or chimney. Both can lead to heat loss when not in use. Close them off if you aren’t using them.
Since you’re likely to have a professional to do the insulation work, the total cost of the work is the real question to ask along with the benefits of each option you’re considering. Ask for comparisons of heating savings too which can help to make your decision easier.
Preventing mold when you insulate your basement
Before you can insulate your home, you need to correct outstanding issues beforehand that may interfere with the long term success of the costly insulation you’re about to install.
If there is a dampness in the basement or water spots on walls, it’s likely you have one of several problems such as a drain back up, cracked or broken pipes or a crack in the foundation or walls that is allowing water to seep in.
In order to prevent moisture in the basement which can lead to mold, get these problems looked at and corrected. Additionally, consider doing the following:
- Measure humidity in the basement to keep it in line with normal which is around 30% – 50%.
- If your humidity is high – particularly in summer when weather can be very humid – use a dehumidifier to remove excess moisture from the air.
- Enquire about the addition of a sump pump in the basement to remove standing water particularly if you live in an older home below the water table.
- Ensure that gutters and drain spouts drain water well away from the foundation of your home.
- Plug cracks in the walls of your basement especially if they appear to already be letting water in.
- If you have a French drain or weeping tiles around the home, ensure they aren’t clogged especially if you live in an older home. They may be clogged, cracked or broken.