Choosing the best insulation isn’t as simple as comparing R-value, however. Spot and seal any leaks for best results.
You’re eager to improve the comfort of your home, and R-value, you’ve been told, is your first stop. Here’s the chart you’re looking for, but before you choose a product strictly on R-value, read on.
This chart shows the approximate R-value per inch of various insulating materials but does not take into account any air leakage that can dramatically affect overall performance.
Almost any type of insulation can improve your home’s performance. Some perform multiple steps simultaneously. Let’s quickly look at the leading insulation product contenders:
The best-known advantage of spray foam’s high R-value per inch of 6.25 (for high-density foam), is that it allows you to pack a lot of insulating power into a small space to create a well-insulated wall. But spray foam has other benefits.
First, it seals air leaks, especially in tough spots, such as around plumbing penetrations and wire entry points. Of course, you pay much more for this premium performance, up to six times per square foot what you do for some fiberglass products.
Spray foam will also be used to seal radon out of basements, and it has been shown to nearly double the hurricane resistance of older roofs. Be sure to allow spray foam insulation to cure before moving back into a space, however. You will need 24 hours for it to set and dry.
Cellulose: Green Filler
For older homes, a major challenge is how to accurately fill all the hidden cavities in walls to improve energy efficiency. With the help of thermal imaging, cellulose can be “blown in” behind walls through a series of small holes in either the interior or exterior walls. (These will be patched when you’re done.)
Some brands of cellulose, such as Greenfiber, include a high percentage of recycled post-consumer waste. At about the same cost as fiberglass, it’s probably the most DIY friendly for major insulation retrofits. If you’re intrepid, you can rent a blower from a big box store, buy many bags of the compressed cellulose fiber, and blast it into your walls and ceiling cavities. It’s a loud, messy job, but affordable and effective.
Fiberglass: Affordable and Stable
Fire-resistant, affordable, resistant to insects, and familiar to most contractors, fiberglass remains the most common choice for insulating. It’s available in blown-in products for both walls and attic cavities, and many manufacturers have changed their manufacturing method so that the tiny fibers are less irritating to the skin, making it easier to apply and more DIY friendly.
Perhaps the most common retrofit use of fiberglass is adding inches of insulation to your attic floor. Research has shown that you probably need a lot more insulation up there than you think. After about R-38, however, your return on investment for additional insulation begins to slow, so don’t think you can just piling it on.
One reason many codes now recommend deeper insulation in attics is because of something called thermal bridging. By covering the ceiling joists completely, the product slows the transfer of heat through the wood or steel.
Mineral Wool: Fire Plus
Mineral wool makers such as Rockwool highlight the fact that their product is virtually impervious to flame. It has many of the same characteristics of fiberglass, with the additional “super power” of extreme heat and flame resistance.
For a home in a wildfire-threatened area, it may be the logical choice. Note that the mineral wool industry has taken some heat lately for mining practices in obtaining raw materials, but we’re hoping they’ll make adjustments toward sustainability. It’s a good product, especially for larger homes, fire-imperiled properties and commercial buildings.
New Homes: Insulation Options Abound
When building new, your insulation options open up significantly. Modern homes have a big advantage over the ones built 20 or more years ago. They typically have exterior “envelopes” that allow fewer air changes per hour, so the wall “system” does not rely as heavily on insulation. New wall sheathings with taped seams, taped housewrap, spray-on housewrap, and other innovations reduce leakage overall, and spot application of sealants and foam seal penetrations effectively.
What this does is flatten the playing field for different types of insulation, and add weight to the R-value rating of each product. In other words, you can achieve good performance with any type of insulation.
The difference now comes down to cost, the amount of cavity space you have available: Are you building with 2x4 inch or 2x6 inch framing? Are you willing to consider parallel wall construction to achieve super high R-values in your walls? Of course, I’m assuming here that you’ve opted for traditional stick framing, not structural insulated panels or insulated concrete forms, which are both sound alternatives.
Ultimately, building codes require a certain amount of insulation for every new home. But you may want to go further--to try to achieve net-zero performance, where you’re able to say your home is “carbon neutral.”
Thermal imaging can identify where walls or ceiling leak energy. In this Arizona house, red areas represent places where hot outdoor temperatures are being transferred indoors. Photo: ReVISION House Scottsdale
How do I decide where to insulate my older home?
The most accurate way to find out is to have a home energy audit performed on your home. This test typically involves a thermal imaging gun and a blower door, and identifies where your home is leaky and poorly insulated. For most homes, the best place to start insulating will be the attic or the foundation walls.But with thermal imaging, you may discover entire wall sections uninsulated, or places where old insulation has settled.
Should I Add Insulation to My House when Replacing Siding?
If you’re going to spend $10,000 to $14,000 to remove and replace the siding on your home, adding insulation makes financial sense. It’s the only scenario in which the siding job will eventually pay for itself in energy savings due to the home’s tighter building envelope.
Your options include: 1. Blowing in cellulose or spray foam, or 2. Adding rigid foam board, such as DuPont/Dow Styrofoam. Either process will greatly reduce air infiltration, at the same time adding some R-value.
An expert on building science, Matt Power has covered construction practices for nearly 30 years, winning dozens of awards for editorial excellence. As Green Builder’s Editor-in-Chief for nearly 10 years, he continues to urge builders and homeowners to new levels of performance and innovation.
Left image: Progressive Foam. Right Image: DuPont
Are Insulating Attic Caps Worth the Cost?
According to Green Builder magazine, some brands of attic door insulation can cut air infiltration by 70 percent. Priced at under $150, they can reduce heating or cooling loss in a home by 20 percent annually. In a home with a $3,000 annual heating bill, that’s a savings of $600 in the first year alone. In other words, the attic cap can pay for itself in energy savings in just three months.
Editor’s Note: This article was originally published January 21, 2015. It has been updated and republished with new information to reflect changes in technology and products.