When measuring or estimating the current amount of insulation in the attic, consider if the insulation is evenly distributed. Uneven or missing insulation degrades the overall R Value, in some cases as much as 50%. Also beware of using old builder specs for the depth and type of insulation.
It is important to check the perimeter of the attic (eves) for proper insulation depth, and also check any duct work that may have blocked access for proper insulation.
You are not doing the homeowner any favors by overstating the depth of their current insulation if it is uneven or poorly distributed.
The data input screen for Attic insulation will determine the base R value on the refine screen.
Calculate the R-value of the attic insulation by multiplying the measurement you took (inches) by a factor based on the type of insulation in the attic. The measurement should be of the lowest depth of insulation.
The Oak Ridge National Laboratory recommends using the following factors for calculating the R value of the insulation, using the depth of the insulation x the factor.
2.5 for loose fiberglass
2.8 for rock wool
3.2 for fiberglass batting.
3.7 for cellulose
6.5 for spray foam (approx)
For example, if the home has cellulose insulation at a depth of 8 inches between the joists, the attic insulation has an R-value of 3.7 times 8, or 29.6. However, if that depth is uneven it could degrade the total R Value.
These calculations are done automatically for you, but it is good to know the bases for the end result and they may be edited on the refine screen.
