Spray Foam R Value Required On Attic

When calculating the r value of a multilayered installation add the r values of the individual layers.

Spray foam r value required on attic.

A typical 2 4 stud filled with open cell spray foam will have an r value between 10 5 and 14. Focusing on spray foam insulation materials there is a difference between the two main types. That means if you used foam it green closed cell which is r 7 per inch it s r value for a 3 5 deep wall cavity would be r 24 5. R value is a measure of insulation s ability to resist heat traveling through it.

However there are open cell spray foam insulation products actually offer r 3 7 per inch such as icynene classic and. Closed cell spray foam insulation. Installing more insulation in your home increases the r value and the resistance to heat flow. Normally in occupied areas all spray foam must be covered by a 15 minute thermal barrier such as thick drywall per code requirements in irc section 316 4 and ibc section 2603 4.

Intumescent coatings are not always needed to coat spray foam in the attic in order to meet code thermal barrier requirements. 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. 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. Recommended home insulation r values.

Know exactly how much you need with our project calculators. It has a lower r value per inch than closed cell foam and is vapor permeable. I m not going to dive into the energy code here but these numbers apply to many climate zones the latter being allowed under the ua tradeoffs rule. The r value of some insulations also depends on temperature aging and moisture accumulation.

The higher the r value the greater the insulation performance. According to industry publication fine home building the r value for open cell spray foam is between r 3 5 r 3 6 per inch. This is very important in situations where your code requires an r 21 for the wall but you only have a 2 4 stud because closed cell spray foam is the only way you would achieve the required r value to meet code. R values are additive so you can multiple the number of inches of insulation thickness times the r value to arrive at a total insulation value.

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. 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. The r value is r 3 5 to r 3 6 per inch so filling a 2 4 cavity yields about an r 13. R value measures how well certain building insulation materials can resist heat.