Scott Jacobs’ 1,100-square-foot Cape is a perfect candidate for an energy upgrade. The 90-year-old house is gutted, and Jacobs wants to insulate it well even if his budget is not unlimited.
“This is my problem,” Jacobs writes in a Q&A post at GreenBuildingAdvisor. “Three companies have provided estimates now. Two say open-cell foam, 7 inches to 8 inches, on the roof and 3.75 inches on the walls. One company just quoted 7 inches of open-cell foam on the roof and 2 inches of closed-cell foam on walls. Estimates vary between $4,500 and $5,500.”
First, Jacobs wonders, how do the 2 inches of closed-cell foam compare with 3 3/4 inches of open-cell foam? And second, for someone with not much money to spend, would installing rigid foam insulation in the rafter bays himself be a reasonable option?
That’s the topic for this month’s Q&A Spotlight.
Open-cell vs. closed-cell foam
Jean-Paul McGraw sums up some of the basic differences between these two types of insulation, including R-values and cost.
“The advantages of closed-cell foam compared to open-cell foam include its strength, higher R-value, and its greater resistance to the leakage of air or water vapor,” McGraw writes.
“The disadvantage of the closed-cell foam is that it is denser, requires more material, and therefore, is more expensive. Even though it has a better R-value, typically the cost per R is still higher than open-cell foam. The choice of foam can also be based on the requirements for the other performance or application specific characteristics such as strength, vapor control, available space, etc.”