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There are several types of foam insulation used in the walls and ceiling of residential and commercial buildings: rigid foam, rigid board made of mineral wool and liquid foam alternatives . Each has certain advantages and disadvantages. This article looks at the first option – rigid foam insulation.
What is it?
Rigid foam insulation, also called foam board or board-stock, is made from foam plastics and is a popular choice for insulating foundations and building exteriors. It can be used inside wall cavities as well. It is sold in rigid board-style sheets of varying sizes. Rigid foam can be supplied with a foil facing to further improve its insulating qualities.
Advantages
- Rigid foam offers very high R-values compared to loose-fill insulation, and some of the best among foam options. Ratings range from R-4 to R-6.5 per inch, even without a foil facing to improve matters.
- Some rigid foam products are water resistant and can be buried to insulate foundation exteriors.
- Expanded polystyrene board ( EPS or "beadboard" ) is the only type which does not use HCFCs in its production, so is the greenest choice.
- EPS can be bought with foil and plastic facings so that it is water resistant and can be used underground.
- Extruded polystyrene board (XPS or "blueboard") has a slightly higher R-value than EPS and is more resistant to moisture.
- Polyisocyanurate board ("polyiso") offers even better insulating value, reaching from R-6.5 to a massive R-8 per inch. It is the least ecological option (see below).
- Polyiso board is manufactured with various facings (plastic or aluminum, for example) to further improve its R-value.
Disadvantages
- Rigid foam insulation in wall cavities must be tightly fitted to stop air infiltration.
- Joints between sheets and boards must be taped to prevent air flow.
- Rigid foam is susceptible to sunlight. UV rays damage it, so it must be stored and installed appropriately.
- The air bubbles inside expanded polystyrene board (EPS or beadboard) stop heat transfer but can accumulate moisture and thus become ineffective. A moisture barrier may be needed, depending on the installation location.
- Basic beadboard is too brittle to be used underground.
- Extruded polystyrene board (XPS or blueboard) uses HCFCs in its production, which deplete the ozone layer.
- Polyisocyanurate board (polyiso) uses the worst HCFCs in its production.
- Polyiso suffers from decreasing R-values over time. At installation it can reach R-9 per inch but, over the following 2 years or so, will reduce to R-7. Foil facing adds R-2 to that.
FAQs
Rigid Foam Insulation Pros and Cons? ›
Cons. Rigid foam insulation can be less efficient if a crack goes unprotected. The result is potentially higher energy costs. Additionally, rigid foam does not expand to fill gaps, so air and moisture leaks are more common.
What are the disadvantages of rigid foam insulation? ›Cons. Rigid foam insulation can be less efficient if a crack goes unprotected. The result is potentially higher energy costs. Additionally, rigid foam does not expand to fill gaps, so air and moisture leaks are more common.
Is rigid foam insulation worth it? ›More effective insulation
With R-values ranging from 3.6 to 8.0, rigid foam sheathing has much better insulation per inch than other materials (i.e. plywood has an R-value of 1.25 and fiberglass batts have an R-value of 3.14).
- High up-front costs.
- Not a DIY product.
- Comparatively long, messy installation process.
- Depending on the type of foam, it can actually absorb water.
- Known and suspected health risks.
- Can make leaks difficult to find and get to.
Due to its firmness and water resistance, rigid foam insulation will generally last 100 years or more.
Do you need vapour barrier with rigid foam insulation? ›In some cases, PIR rigid foam insulation may be combined with other types of insulation, such as batt insulation. In these situations, it may be necessary to use a vapour barrier to ensure proper moisture control and prevent moisture from building up between the insulation layers.
Is a vapor barrier needed with foam board insulation? ›Vapor barriers are often installed in basements and crawl spaces to prevent ground moisture from leaking in. In houses with spray foam insulation, however, vapor barriers are not necessary.
Does rigid foam need a thermal barrier? ›ALL FOAM SHOULD BE COVERED BY A THERMAL BARRIER WHEN USED INSIDE A HOME.
What is the R-value of 3 inch rigid foam? ›| Thickness (Inches) | R-value (in I-P/Imperial) | RSI (R-value in Metric) |
|---|---|---|
| 2.5 | 15.5 | 2.7 |
| 3.0 | 18.6 | 3.24 |
| 3.5 | 21.7 | 3.78 |
| 4.0 | 24.8 | 4.32 |
Rigid foam R-values range from R-1 for 1/4-inch thick sheathing panels to R-15 for 3-inch thick panels. R-value is not entirely a function of the thickness of the material, as the facing material and type of foam used will affect the R-value of the material.
When should you not use spray foam insulation? ›
DON'T use expanding foam around outlets and recessed can lights. In the quest for a draft-free home, it's natural to want to add some insulation around electrical outlets, but expanding foam might not be the best type of insulation there.
What is best attic insulation? ›Fiberglass batt is considered to be the best insulation for attics. Compared to other insulation materials, it is the cheapest and easiest to install. Fiberglass batt is also incredibly energy efficient, as it helps to slow the spread of hot and cold air.
What is the disadvantage of foam? ›Like rubber, it is highly responsive and has a bounce that some sleepers love and some others hate. Pros: Depending on the foam type, it can be quite comfortable, safe, and responsive. Cons: Lower quality foams can break down quickly, causing sagging issues within only a few months or years.
Is rigid foam insulation a fire hazard? ›Rigid polyurethane and polyisocyanurate foams will, when ignited, burn rapidly and produce intense heat, dense smoke and gases which are irritating, flammable and/or toxic.
Is rigid foam insulation better than fiberglass insulation? ›Rigid foam insulation packs in more R-value per cubic inch than fiberglass insulation does. If conserving energy is your main goal and there are no other influencing factors such as moisture, rigid foam may be your first choice.
Is spray foam better than rigid insulation? ›Exceptional moisture control: Spray foam fills a space better than rigid board, making it a better insulator against moisture. This can be valuable in humid climates. Longevity: Insulation can be complicated to replace, but spray foam is designed to last a long time.