Spray Foam Insulation R Values

The r value of closed cell foam is r 6 5 7 per inch.

Spray foam insulation r values. Contractors often use it to insulate under slabs ceilings walls and roofs. Insulation materials run the gamut from bulky fiber materials such as fiberglass rock and slag wool cellulose and natural fibers to rigid foam boards to sleek foils. 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. For example if you have a type of insulation that has an r value of r 5 per inch of thickness you will need a depth of 6 inches of this insulation installed in your attic to reach r 30 if you live in zones 2 or 3.

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. 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. Bulky materials resist conductive and to a lesser degree convective heat flow in a building cavity. Closed cell spray foam has a far better r value per inch than other less effective insulations like cellulose fiberglass or even open cell foam.

Rigid foam boards trap air or another gas to resist conductive heat flow. Insulation r value measures how well a particular insulation resists heat flow. Open cell spray foams are between 5 and 1 lbs per cubic foot and have an r value of 3 0 4 0 per inch of insulation. All these have r values ranging from r 3 2 to r 3 8 per inch.

These r values are a sum meaning this should be the total r value once you add up the entire depth of insulation. 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. Spray foam the truth about r values r value does not measure heat movement carried in the air. The r value for open cell is typically around 3 7 at 1 thick and varies by manufacture.