Choosing a bad spray foam contractor in Oregon could cost you a lot more money than you think. Make sure you get the right advice from a trusted and reputable spray form contractor. The cost of re-installing spray foam insulation will be costly, make sure you make the right decisions from the start. Following the guidance on the thickness of the spay foam backed up by research and data.
Some companies in Oregon are recommending 2“ on the roof deck - here in the Northwest we know that it takes 3“ to eliminate the dew point. The minimum installed thickness of Closed Cell Polyurethane Spray Foam Insulation is 2“ closed cell spray foam in the walls and 3“ closed cell spray foam under the roof.
The Energy Modeling Agency
Above is the Heat Flow Reduction chart that illustrates why there is no need to install any more than 3“ closed cell spray foam. This amount provides a heat flow reduction of 96%. If we double that thickness, the heat flow only goes up a little over 1% which equated to an almost immeasurable/insignificant amount of energy savings. This is the diminishing rate of return of foam and why we only recommend 2“ closed cell spray foam in the walls (94% heat flow reduction) and 3“ closed cell spray foam under the roof.
While you will receive a 94% heat flow reduction with only 2“ of closed cell spray foam insulation, we recommend a minimum of 3“ under and roof deck or in any attic assembly.
This is due to 2 factors:
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A typical roof assembly is subject to a significant increase in temperature due to the radiant heat gain from the solar exposure of the roofing material. The 3“ of Closed Cell Spray Foam will guarantee the 96% heat flow reduction which is needed for this increased heat gain.
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Large temperature swings in a roof assembly could cause an increase in moisture or vapor drive and the 3“ of Closed Cell Spray Foam will almost eliminate the thermal drive which carries the moisture. (Vapor drive=latent moisture driven through an assembly by a thermal drive). This Vapor drive will vary from area to area based on the climate zones and the average heat days per year and is generally calculated by a WUFI scale for condensation.
Ken AshcomEnergyModelingAgency.com
Common Questions
Why does re-installing cost more than the original job?
Cured foam bonds to the framing and sheathing, so removal is slow manual work before any new material goes in. Access is often harder the second time, and anything damaged by the original problem has to be dealt with first.
Can thin foam simply be sprayed over?
Sometimes, where access allows and the existing layer is sound. Where the original install caused moisture damage, adding depth over the top traps the problem rather than solving it.
How do I avoid needing this?
Get the thickness right at the specification stage and make sure the whole envelope is priced, not just the easy surfaces.
Related: why we specify 3 inches on a roof deck · roof-deck insulation
Also worth reading: why 3 inches on a roof deck, examples of bad spray foam work.
Talk it through with an installer
Every building is different. Tell us about the property and we will give you a straight answer on what it needs.