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Frequently Asked Spray Foam Questions

1. What are the proper thicknesses for open cell and closed cell spray foam applied in an attic?


What are the proper thicknesses for open cell and closed cell spray foam applied in an attic? How does this compare to building code prescribed R-values?

The proper thickness for spray foam applications in an attic vary depending on the difference in temperature between the interior and the exterior. There comes a point of maximum efficiency when added foam doesn't provide cost effective insulation.

For example, in South Texas where temperatures average 95 degrees, and with a cold storage temperature of -10 degrees, the cost effective thickness of closed cell SPF is approximately five to six inches.

However, the thickness of maximum efficiency may not match the building code prescribed R-values. This is because most building codes are based on fiberglass insulation, not spray foam, which is often more efficient. In fact, SPFA has conducted comparison tests in attics and walls that show a 20 to 35 % greater energy efficiency than fiberglass insulated walls and attics in similar climate conditions.

Five inches of open cell foam to the underside of the attic will provide an R-value of approximately 19 - 20. Two inches of closed cell foam will provide an R-value of approximately 12 - 13.

Although these thicknesses may be adequate in certain situations, your code official may insist on full R-value thickness of 38 unless you provide them with research data that demonstrates the fact that lesser R-values of spray foam provide the equivalent insulative value of other insulation with higher R-values.


2. Does spray foam gives off any VOC gases?


Sprayfoam is not considered to be a VOC emitter as are a lot of adhesives and solvent based paints. During application some VOCs may be released but after curing the it is very difficult to measure any chemical emissions from the foam. Many suppliers have performed testing on their foams. All of the foams in Canada are required to have testing for VOCs. Check with the foam supplier for additional data.


5. Which is better, closed or open cell?


Both systems offer significant advantages over fiberglass batting: ability to air seal; ability to fill cracks and conform to odd shaped cavities; and ability to hold their shape over time and under adverse conditions.

But only closed-cell foam has the thermal insulation value (R-value) to bring your home up to Energy Star® standards with only one-half the thickness required for fiber insulations. In addition, closed-cell foam products increases the strength of you wall system (it's approximately doubled) and increase the water resistance of your home's exterior. Open cell insulation is less expensive and provides supplier sound deadening characteristics.

6. How does SPF reduce energy use in buildings?

  • SPF provides a continuous air barrier.
  • SPF prevents moisture infiltration through air leakage.
  • SPF minimizes dew point problems and condensation.
  • SPF avoids thermal bridging.
  • SPF resists heat movement in all directions.
  • SPF provides reliable performance under varying conditions.


7. What is the difference between a vented and unvented attic?


Unvented (conditioned) attics use air-impermeable insulation as a barrier to prevent moisture condensation on the underside of roof decks. Vented attics minimize condensation by allowing the escape of moisture to the exterior by air flow.


8. If you spray the underside of a roof deck with SPF insulation, should you vent the attic?


No, the application of SPF insulation to the underside of the roof deck minimizes the potential for condensation. The SPF insulation develops a thermal and moisture gradient that avoids the development of dew point conditions in the attic. Because of this, moisture won't condense or accumulate and, therefore, does not need to be vented to the exterior.


9. Do you need a vapor retarder or a vapor barrier with SPF insulation?


It depends of the use of the building, the climate and the materials of construction. In normal occupancies and moderate climates, SPF insulation typically does require a vapor retarder. Extremes of climate and building use may require vapor retarders/barriers. Check with your design professional for specific recommendations and refer to SPFA technical document, AY 118, Moisture Vapor Transmission for further information.


10. Is SPF a good soundproofing material


Both low and medium (2lb/cubic/ft) density SPF effectively reduce noise from outside sources by sealing cracks and gaps that allow sound to travel through the walls, floors and ceilings into the building. They are less effective against noise caused by vibration.


11. What is the difference between low density, open cell SPF and medium density closed cell SPF?

  • 1/2 lb Spray Polyurethane Foam (SPF)
    Low density, open cell SPF refers to a generic spray polyurethane SPF that weighs between 0.4 to 0.6 lbs per cubic ft when fully cured. It is spray applied to a substrate as a liquid and expands about 100-150 times its original volume to form a semi-rigid/flexible, non-structural SPF insulation. The SPF has an R-value around 3.5 per inch and typically uses water as the blowing agent.
  • Medium Density, Closed Cell Spray Polyurethane Foam (SPF)
    Medium density, closed cell SPF used in interior applications typically refers to generic spray polyurethane foam that weighs between 1.5 to 2 lbs per cubic ft when fully cured. It is also spray applied as a liquid to a substrate and expands about 35 to 50 times its original volume to form a rigid, structural SPF insulation with a compressive strength between 15 to 25 PSI. The SPF has an R-value of around 6.0 per inch (aged R-value) and uses high R-value blowing agents.
  • Similarities: Both products are excellent air barriers in buildings, provide great insulation, can assist in the control of condensation within buildings and have great environmental benefits.


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