R Value Of Attic Spray Foaam

Wood has an r value of about one per inch of thickness.

R value of attic spray foaam.

Encapsulating the rafter or top truss chord roof framing members with spray foam will improve the energy efficiency of the attic space. R value is a measurement of thermal resistance and measures the ability of heat to transfer from one side of an object to another. So let s find out what you need and discuss how you can get there effectively but also cost efficiently. The r value of closed cell foam is r 6 5.

Open cell spray foam r values. Add insulation to attic. The r value of spray foam insulation is approximately 6 per inch so those using spray foam as their insulator will need about 6 3 inches of thickness to reach r 38. 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.

Two inches of closed cell foam will provide r12 r14 of insulation. This is more common with closed cell foam but it happens with open cell foam too. When determining how much insulation you need don t guesstimate calculate. It performs much better than any form of batt for stopping air flow but it is not as complete of an air seal as closed cell spray foam.

All these have r values ranging from r 3 2 to r 3 8 per inch. Spray foam isn t thick enough. The r value of fiberglass insulation is approximately 2 2 per inch so much thicker fiberglass insulation is required to achieve the same r value of 38. Open cell spray foam absorbs and holds water.

Spray foam contracts and pulls away from framing. As a benchmark one inch of solid wood has an r value of 1. How long does spray foam r value last. In comparison an inch of blown fiberglass insulation has an r value of 3 1 3 4 and an inch of blown cellulose in an attic has an r value of 3 2 3 7.

It has a lower r value per inch than closed cell foam and is vapor permeable. Closed cell spray foams are between 2 and 4 lbs. Existing 3 4 inches of insulation. R value measures how well certain building insulation materials can resist heat.

Recommended insulation levels for retrofitting existing wood framed buildings. Just like for open cell foam r values are additive. Open cell spray foam typically has an r value of 3 5 per inch and it should be noted that open cell does not form a tight air seal. The r value is r 3 5 to r 3 6 per inch so filling a 2 4 cavity yields about an r 13.

This is because the effects of thermal bridging are limited which also results in the elimination of melt lines on the roof surface in cold climates. They sport an r value of 6 0 8 0 per inch of insulation about double their open cell foam counterparts. Closed cell spray foam insulation.