This guide to rigid insulation discusses the product, its uses and costs. Rigid foam insulation offers good insulation value per inch of thickness, so it’s a popular choice where getting the most insulation for the space is important.
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About Rigid Insulation
There are several types of rigid foam insulation. The most commonly used are polystyrene, either expanded polystyrene (EPS) or extruded polystyrene (XPS). The third type is polyisocyanurate rigid foam board, referred to in the industry as ISO.
Here’s how they compare. EPS is the least expensive, but has an R-value of only R-4 per inch of thickness. It may absorb water, so cannot be used as a vapor/moisture barrier. EPS is unfaced, so if applied to the exterior of a home, it should be used over house wrap such as Tyvek.
XPS is slightly more costly, but gives a superior value of R-5 per inch. Extruded polystyrene may be faced or unfaced, depending on the application. XPS is a vapor retarder, but not a vapor barrier.
Polyisocyanurate (ISO) is the best rigid foam insulation in some ways. The R-value is R-8 per inch of thickness, but this value will degrade by R-1 or R-2 over time before stabilizing. Foil-faced ISO is impermeable, so may be used as a vapor/moisture barrier. If installed with a foil face on the outside of a building, faced insulation should not be used in the wall cavity because it will trap moisture between the two barriers and cause rot and mold.
The Value of Rigid Foam Insulation
Rigid foam offers good insulation per inch of thickness. It is lightweight and easy to work with. The boards, usually 4×8 feet, can be scored and snapped or cut with a saw. They can be installed using adhesive, and the seams are usually caulked and taped. Rigid insulation is easily cut to fit for small spaces.
Locations for Rigid Insulation
Foam board insulation is often used on the outside of foundations or against foundations in the interior. When used on the interior of a finished basement, it is often glued to the foundation before the walls are framed over it.
Rigid foam insulation is also used to sheath houses over the OSB or plywood sheathing and beneath the home’s siding. It can be used in ceilings and attics, but is not the most cost-effective choice for those applications. Foam board is also used in floors where space is tight.
The Cost of Rigid Foam Insulation
This product falls on the upper end of the insulation prices spectrum. Here’s a look at rigid insulation cost for various R-values.
Table 1: Prices shown for Rigid Foam Insulation, divided down into Material per Sq. Foot and Labor per Sq. Foot:
| Insulation Rating | Material per Sq. Foot | Labor per Sq. Foot |
| R-13 | $0.75 to $0.90 | $0.90 to $1.25 |
| R-19 | $1.10 to $1.30 | $0.90 to $1.30 |
| R-21 | $1.20 to $1.45 | $0.95 to $1.30 |
The cost for additional supplies and materials will be $45 to $65 per $1,000 square feet of space covered by the insulation. These materials include caulk insulation and tape for the seams where rigid boards adjoin one another.
To assist you with your home insulation project, we’ve setup a simple system where you can request a set of quick price estimates from local contractors near you.