How Thick Should Spray Foam Insulation Be In Attic

Department of energy recommends insulation levels relative to the climate zone and part of the structure being insulated.

How thick should spray foam insulation be in attic. Unvented attics sometimes called sealed enclosed or encapsulated attics feature insulation on the underside of the roof decking rather than on the attic floor. Spray polyurethane foam is a chemical product that is created by two materials isocyanate and polyol resin that will react with each other when they are mixed and will expand up to 30 to 60 times its liquid volume as it is sprayed in place. It is also essential to examine the degree of moisture permeability that is needed. This is fine for areas where r 21 or less is required but if the area requires a higher r value than 21 the testing approvals won t allow it maximum thickness limitations for cured foam maximum thickness limitations for cured spray polyurethane.

The rapid growth of sprayed foam insulation in building construction thanks in part to its immediate and long term. So to answer the question how thick should spray foam insulation be the answer depends on certain factors. This is more common with closed cell foam but it happens with open cell foam too. A lot of builders and homeowners are going with spray foam insulation because of the airtightness benefits but then the questioner mentioned that the spray foam contractor had intentionally left big holes to the outside by not sealing the gable vents.

Since closed cell foam has a higher r value per inch installers generally spray 2 in walls and 3 in rooflines to meet the energy code requirements of r 13 and r 19 respectively. I have recently had close cell insulation sprayed in a metal building the contractor was suppose to install 2 of foam and states they sprayed 5 coats of insulation however the actual thickness is 1 1 1 8 he is claiming the foam did not expand as it should have but that the material for a 2 of foam has been sprayed. Since the protocols for testing u and r values don t take into account nearly 0 infiltration losses of foam compared to fiberglass or loose fill insulation. Spray foam insulation thickness study the sciene of spray foam and you find it s not necessary to spray more than 4 inches of closed cell foam in any installation.

So if the ideal r value for your home is r 40 your contractor may only need to spray five inches of foam insulation. This is compared to having to stack fiberglass as high as 14 16 inches to get the same results. Although spray foam insulation has been in use since the 1940s primarily for aircraft for the past 30 years continual product innovation has seen the increased adoption of spray foam insulation in residential and commercial construction. Allowable of the spray foam in an attic is 6 inches.

Earlier this year i got a question about a home that had spray foam insulation in the attic. The unvented attic space is considered the most effective and up to date building practice particularly by the spray foam industry.