Green Building - Problems with Spray Insulation
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Green Building - Problems with Spray Insulation

Facts about spray foam insulation including ventilation requirements, insects, fire concerns, and costs are discussed.

Spray foam is a popular choice to insulate interior walls and attic spaces as it forms a uniform vapor barrier and insulating layer as well as sound attenuation.

Spray insulation is polyurethane or icynene foam that is sprayed into the space between walls and floors to insulate homes and commercial buildings. Many builders like this type of insulation since it fills in gaps and prevents air infiltration.

Like every building material, foam insulation has pros and cons. Although there are benefits to using spray insulation, there are also some problems with the material. Spray foam insulation is an excellent building material as long as it is installed according to the manufacturer’s specifications and the installers are trained and certified by the manufacturer.


Spray insulation must be applied with specialized equipment that such as a high pressure spray gun. Most spray foams are comprised of two parts that are mixed right at the end of the spray gun. The insulation comes out as a liquid that expands and hardens as it is exposed to air. As the foam is sprayed into the cavities between walls and ceilings, it can adhere to other surfaces that are not covered. Cleanup is challenging if the foam finds its way onto brick or stone surfaces, and spraying foam insulation typically requires the use of protective plastic as well as protective clothing.

Foam that expands beyond the face of the wood framing can be trimmed off flush with a hand saw, reciprocating saw, or a wire.


Insulation Saw

Trimming spray foam insulation with a reciprocating saw

Installation Problems

Spray foam installation is challenging to handle without practice. Spray insulation expands rapidly as it dries and if too much foam is sprayed into the walls, the rapid over-expansion can cause the walls to buckle or even crack and result in damage.

Electrical boxes need to be protected to prevent foam from expanding into the box. All wiring needs to be completed before spray foam insulation is installed. NEC 110.12 (c) states "Internal parts of electrical equipment shall not be contaminated by foreign materials..."


Spray insulation is significantly more expensive than fiberglass installation. A homeowner who wishes to spray insulation himself is forced to rent expensive spray insulation equipment to complete the job, however there are small kits available that may be more suitable for do it yourself projects. In addition, waste expenses can increase the cost of spray insulation. Spray insulation is sprayed into the open spaces between wall studs and floor and ceiling joists. As the insulation dries, it expands beyond the studs, and the home owner or installer is forced to trim away the excess to make it flush. The expense of excess insulation waste is often substantial.

According to, as of September 2010, expect to pay between $1.35 and $1.50 to insulate a square foot of wall and between $1.65 and $1.85 to insulate a square foot of roof decks with Icynene foam insulation.


Do it Yourself Spray Foam Kit


Since the spray foam adheres to the surfaces it is spray on, removal can be difficult in the event you have to perform repairs or plan on additions or alterations to your home. Unlike fiberglass insulation that removes easily if needed, spray insulation removal requires cutting or scraping to separate the insulation from the building surface.


Spray foams have almost no volatile organic compounds (VOC) present after the foam has cured, about one month. However, if there is not sufficient ventilation for the home, the indoor air quality (IAQ) can suffer without the removal or indoor air pollutants and moisture. Make sure there is adequate make-up air for your furnace, boiler, hot water heater, and exhaust fans. The best solution is the use of sealed combustion appliances. If this is not possible, adequate outside air should be ducted to each appliance to prevent back drafting.



Icynene foam insulation is easily penetrated by insects, including carpenter ants, moths and termites. Insects damage the structural integrity of foam insulation. The insects reduce the insulation's effectiveness and lower its thermal performance. Icynene foam insulation typically requires additional chemical or mechanical treatments to improve its resistance to insects. Borates can be added to the foam to prevent insect damage. Most specifications require that the spray foam should not come in contact with wood that can become wet as carpenter ants and termites can begin nesting in the wood and then continue into the spray foam insulation.

Fire Concerns

Although the material itself does not contribute fuel to fire, the insulation will burn completely if exposed to burning flames for more than 15 minutes. Fire resistance usually refers to the system, which includes wall finish, such as gypsum wallboard. There are fire retardant spray foams on the market but they may not be required for your application.

There was also a recent story about fires occurring during the installation of the foam when excess heat generated by the exothermic reaction that occurs during the installation of spray polyurethane foam caused several houses to catch fire. Fire investigators assume that installers applied the spray foam too thickly which trapped the heat generated by the chemical reaction that creates the foam.

Read the complete story here:

Caution should be taken when installing spray foam over fixture housings or wiring carrying large loads, such as in older homes with suspect wiring or large air conditioning units. Excessive current can cause excessive heat, which can cause polyurethane foam to carbonize and create an arcing path, thus leading to fire.

Educate yourself and make sure you are aware of the benefits and costs of using spray foam insulation. As long as you understand the requirements you can make the best decision for your project.


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Comments (3)

Good information to know. voted up

You have provided some very vital information about the use of spray insulation and batting insulation. Thank you for your expertise.Promoted.

I always enjoy your articles, Daniel. This article is actually very timely for me - thanks for sharing your knowledge.