Contaminated insulation in a crawl space © Daniel FriedmanCrawl Space Insulation Retrofit - Spray Foam

  • CRAWL SPACE INSULATION RETROFIT - CONTENTS: What insulations work best for crawl area retrofits?Using Polyurethane Foam or Icynene® Insulation for Crawl Space Insulation Retrofits. Sprayed-Foam Polyurethane Insulation. Rigid Polyurethane Foam Board Insulation for New & Retrofit Insulation Jobs - troubles, solutions. Insect Attack on Foam Insulated Foundations
  • POST a QUESTION or READ FAQs about adding crawlspace insulation using foam

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Crawl space insulation improvements - retroffitng insulation into the crawl area:

This article describes several alternative processes for adding crawl space insulation and the use of spray foam insulation in crawl areas. We include photos that compare spray foam insulation with cut-and-paste foam board insulation.

Our page top photo shows why you would want to remove old fiberglass insulation, then clean, and properly insulate an existing crawl area, but the advice below pertains to new construction as well.

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Crawl Area Insulation Retrofits - OK to use Spray Foam

A variety of foam building insulation products are marketed for insulating crawl areas, as we review here.

Foam insulation sprayed in a crawl space - this is not mold - Daniel Friedman 04-11-01 Icynene spray foam being tested for air leaks (C) D Friedman

Using Polyurethane Foam or Icynene® Insulation for Crawl Space Insulation Retrofits

at ICYNENE FOAM SPRAY INSULATION we discussed the properties of Icynene® foam insulation (and similar products). This foam is a spray-in-place product, injected through openings, or pour-in expanding-foam insulation product. Other water borne foam spray insulation products, including some latex-foams, are available.

Our photo (left) illustrates the author testing for air leaks at an apparent void in foam insulation sprayed in a tight crawl space.

Where access is very restricted it can be difficult to spray any foam in a smooth, uniform, and airtight pattern. Our next photo (below left) illustrates a mixed-media insulation retrofit in a crawl area.

At URETHANE FOAM Deterioration, Outgassing we discussed some historic concerns surrounding polyurethane foam insulation, including the water resistance of open-celled spray foams, outgassing, and insect resistance.

Icynene foam sprayed in attic (C) D FriedmanBut there are modern spray polyurethane products that are closed-cell insulation suitable for use in damp locations and that may perform well in a crawl space, avoiding the issues we discussed above as well as the issue of mold formation in fiberglass insulation.


and  MOLD in FOAM INSULATION for details about mold problems in building insulation.

See How to Make a Sure Distinction Among UFFI, Icynene, and Latex Foam Insulations for more detail on the identification of these individual foam insulation products in the field

Here is what the U.S. Department of Energy says about polyurethane insulation in buildings - (the US DOE comments are consistent with our text above):

Polyurethane is a closed-cell foam insulation material that contains a low-conductivity gas (usually hydrochlorofluorocarbons or HCFC) in its cells. The high thermal resistance of the gas gives polyurethane insulation materials an R-value typically around R-7 to R-8 per inch.

Over time, the R-value of polyurethane insulation can drop as some of the low-conductivity gas escapes and air replaces it. This phenomenon is known as thermal drift. Experimental data indicates that most thermal drift occurs within the first two years after the insulation material is manufactured. The R-value then slowly decreases. For example, if the insulation has an initial R-value of R-9 per inch, it will probably eventually drop to R-7 per inch. The R-value then remains unchanged unless the foam is damaged.

Polyurethane insulation is available as a liquid sprayed foam and rigid foam board. It can also be made into laminated insulation panels with a variety of facings.

Sprayed-Foam Polyurethane Insulation

Sprayed or foamed-in-place applications of polyurethane insulation are usually cheaper than installing foam boards. These applications also usually perform better since the liquid foam molds itself to all of the surfaces.

All closed-cell polyurethane foam insulation made today is produced with a non-CFC (chlorofluorocarbon) gas as the foaming agent. Some polyurethane foam combines with a HCFC gas. These types don't insulate as well as insulation made with a CFC gas, but the non-CFC gas is less destructive to the ozone layer. However, these foams still have an aged R-6.5 per inch thickness. Their density is generally 2.0 lb/ft3 (32.0 kilograms per cubic meter [kg/m3]). There also are low-density open-cell polyurethane foams (0.5 lb/ft3 [8 kg/m3]). These foams are similar to conventional polyurethane foams, but are more flexible. Some low-density varieties use carbon dioxide (CO2) as the foaming agent.

Low-density foams are sprayed into open wall cavities and rapidly expand to seal and fill the cavity. One manufacturer offers a slow-expanding foam, which is intended for cavities in existing homes. The liquid foam expands very slowly and thus reduces the chance of damaging the wall from overexpansion. The foam is water-vapor permeable, remains flexible, and is resistant to wicking of moisture. It provides good air sealing and yields about R-3.6 per inch of thickness. It is also fire resistant and won't sustain a flame.

Soy-based, polyurethane liquid spray-foam products are also available. The cured R-value is around 3.7 per inch. These products can be applied with the same equipment used for petroleum-based polyurethane foam products.

Rigid Polyurethane Foam Board Insulation for New & Retrofit Insulation Jobs

Crawl space insulation with foam board (C) D Friedman

Foil and plastic facings on rigid, polyurethane foam panels can help stabilize the R-value, preventing thermal drift.

Testing suggests that the stabilized R-value of rigid foam with metal foil facings remains unchanged after 10 years.

Reflective foil, if installed correctly, can also act as a radiant barrier, which adds another R-2 to the overall thermal resistance.

Panels with foil facings have stabilized R-values of R-7.1 to R-8.7 per inch.

Readers considering adding insulation inside or outside a basement or crawl space foundation wall should also


Foam board insulation job (C) D Friedman

Also notice the trouble we had retrofitting solid foam cut boards around the waste pipe when working in a tight crawl area.

You might ask why we didn't cut a perfect-fitting rounded or notched board section to fit on either side of the waste pipe (photo at left).

Try hauling a bundle of 2-inch foam board slabs down into a tight crawl area (photo below left) that requires contortions just to enter or exit the space. Add working alone.

And ask yourself how many trips you would be willing to make crawling in to measure, out to cut, in to test-fit, out to adjust each cut.

You can see from the photo (below left) that this was a tight area - putting down plastic not only helped the installer (me) move around in the crawl area, it helps keep the crawl area dry.

Tight crawl areas (C) D FriedmanBut the cut and paste approach shown above was not very nice.

A better approach may be to use the cleat and nail support system we show here, but to make a final pass with a few cans of spray foam or spray fireblock foam insulation to complete the job.

Readers interested in the mold resistance properties of foam insulation should see ICYNENE FOAM SPRAY INSULATION.

Insect Attack on Foam Insulated Foundations

Wood destroying insect effects of foam insulation: foam insulation is not an insect barrier; while these materials do not provide food for termites, they are easily penetrated by termites or carpenter ants (as are other insulating materials). For this reason our opinion is that it is bad design to bring foundation insulating foam panels up into contact with building wood framing materials unless an approved insect barrier has also been installed.

What can we do to improve the insect resistance of buildings where solid foam board or foam spray foundation insulation are being applied? Having read our recommendations and warnings at Insects & Foam Insulation, reader S. Frank asked if insulating a crawl space with spray foam would create a risk of insect attack on the building.

The insect path formed by foam, such as foam board on the outside of a foundation and brought up in contact with wood framing, can be a risk to a building, especially if wood destroying insects are common in the area and if other factors such as water conducive to insect attack are present. Insects don't "eat" the foam but it can provide a protected pathway up from soil into wood structural elements.

Otherwise you should consult with a local pest control professional to discuss whether or not a pre-treatment or installation of termite shields are necessary.


Continue reading at MOLD in FIBERGLASS INSULATION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see CRAWL SPACE GROUND COVERS for proper use of ground covers in crawl areas and for discussion of spraying foam on the dirt in a crawl area



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CRAWL SPACE INSULATION RETROFIT at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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