Spray Foam and Existing Insulation

Fiberglass and Foam spray foam performance

A question commonly asked by Architects, Contractors, and Homeowners:

“Do we have to remove the existing insulation if we are going to upgrade our attic to Spray Foam?”

We are a society that has been programmed to think that more is always better, but when it comes to existing insulation and spray foam that is not the case.  Traditional insulation whether it is fiberglass or cellulose should be removed in order to keep the attic cooler and help the spray foam insulation perform to its maximum potential.

Foam requires a complete restriction of air movement.  The goal of a qualified foam contractor is to completely restrict air from infiltrating from the outside of a structure to the inside of a structure.  Therefore, anything that would allow air to infiltrate into a sealed environment would have ill effects on the performance of the attic.  The air allowed to infiltrate would condense at the ceiling plane (where the hot air and cold air below would touch).  This would cause a line of condensation (water) to build up.  Water is one of the main items needed for the growth of mold, the corrosion of metal, and the odor attributed with decay.  The position of all foam manufacturers as it relates to removal is “Yes, with no exceptions.”

Fiberglass and Foam

The above picture is from an existing home purchased that was being remodeled.  This picture shows in detail air infiltration due to non-removal of existing insulation.  The fiberglass was not removed and foam insulation was sprayed directly on top of fiberglass allowing air to infiltrate into attic.  A 6ft x 10ft hole was created to allow air to infiltrate.

It is safe to assume that the cost of having this foam installed did nothing toward making the home more energy efficient.  The odds that it created more problems than it fixed are greatly enhanced.  The practice of low cost spray foam sales with no knowledge of the effects as it relates to the structures performance increases the opportunity for mold buildup, metal deterioration, equipment damage as well as the possibility of insect and vermin infestation.

 

 

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