Spray Foam R Value Required On Attic

Recommended home insulation r values.

Spray foam r value required on 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. Insulation level are specified by r value. 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. Know exactly how much you need with our project calculators.

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. 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. The higher the r value the greater the insulation performance. It has a lower r value per inch than closed cell foam and is vapor permeable.

Installing more insulation in your home increases the r value and the resistance to heat flow. 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. When calculating the r value of a multilayered installation add the r values of the individual layers. The higher the r value the better the thermal performance of the insulation.

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 of fiberglass insulation is approximately 2 2 per inch so much thicker fiberglass insulation is required to achieve the same r value of 38. R value measures how well certain building insulation materials can resist heat. 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.

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. Focusing on spray foam insulation materials there is a difference between the two main types. Closed cell spray foam insulation. The r value is r 3 5 to r 3 6 per inch so filling a 2 4 cavity yields about an r 13.

The r value of some insulations also depends on temperature aging and moisture accumulation. Intumescent coatings are not always needed to coat spray foam in the attic in order to meet code thermal barrier requirements. When determining how much insulation you need don t guesstimate calculate. 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.