Spray Foam Insulation – Advantages and Disadvantages

by Erik North on December 31, 2010


If you are thinking of insulating your home, then you will want to know the different types of home insulation. One type is fiberglass insulation and another type is spray foam. What is spray foam and what are its benefits and drawbacks? Does spray foam prevent heat loss and how?

Spray foam is one of the most versatile forms of insulation available. It can seal your home from air and moisture intrusion, strengthen building structure and provide thermal, air and vapor barriers useable in all U.S. climates.

Advantages of Spray Foam Insulation

Disadvantages of Spray Foam Insulation

  • More expensive than other common insulations
  • Should be installed by a professional contractor
  • Foam propellants can be very non-green

Types of Spray Foam Insulation

There are many different types of spray foam that fall into two broad categories: Open Cell and Closed Cell foam. Open cell is foam where the tiny cells of the foam are not completely closed. They are broken and air fills the open spaces of the foam. This causes open cell foam’s spongy feel.

With closed cell foam, its tiny foam cells are closed and packed together. They are filled with a gas, causing a greater density, have a higher insulating value and can act as an air and vapor barrier. Open cell foam typically weighs 0.5 lbs./cu. ft. compared to 2.0 lbs/ cu ft for closed cell.

Advantages of Spray Foam

Sprayed closed cell foam has an aged R-value of approximately 6.0 per inch thickness (depending on the particular formula and application; higher values have been achieved). Open cell foam has an aged R-value of around 3.5 per inch.

While both open and closed cell can act as an air barrier, open cell has a much higher permeability and is not a vapor barrier. As such, open cell should not be used below the ground level grade or other higher moisture applications. Also, in Climate Zones 5 and greater, open cell foam (and any vapor permeable insulation material) requires a vapor barrier, usually standard drywall which doubles as the ignition barrier.

Because sprayed foam can act as an air barrier, it can drastically reduce air leaks. Studies have shown that as much as 40% of a building’s total energy loss is due to air exfiltration. Traditional fiberglass insulation, typically just fastened into the wall cavities, does not seal the wall cavities. Air infiltration can pass through these gaps. Spray foam adheres and forms to the walls and floors to create a tight seal and insulating barrier that stops air leaks.

Disadvantages of Spray Foam

Spray foam insulation does provide insulation and air sealing in one product but does not come without draw backs. It is expensive compared to either cellulose or fiberglass; approximately twice the cost on an equivalent R-value basis. One of the sources of fiberglass’ enduring popularity is its ease of installation. Any weekend home craftsman can install fiberglass in fairly short order. To achieve the best results, spray foam must be installed by experienced professionals, familiar with the time and temperature specs of foam installation. Lastly, spray foams use different propellants from water to not exactly ‘green’ gases like pentane.

Spray foam is a great tool in the insulator’s tool box. It insulates and air seals and can provide superior whole home performance in most any climate. Knowing the benefits and drawbacks can help making smart decisions for your home.

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