Obviously in this blog, my focus is on energy efficiency and making a home environment comfortable and healthy. So when I think about building or renovating a home, I think how can I make this home more comfortable, more energy efficient within reason (which usually means within financial reason) as opposed to what is the LEAST AMOUNT OF INSULATION I can get away with.
Energy standards for residential buildings are covered by the International Energy Conservation Code (IECC). These codes are updated every 3 years and adopted by individual states in the US. You can see in the map below that the majority of the states in the US are covered by the IECC 2009 code (states in blue). That's true for SC where I live.
Adoption of International Energy Conservation Codes by State
International Energy Conservation Code Zone Map
So what does that mean in terms of actual energy conservation? Specifically, for South Carolina that means that my attic should be insulated to an R-value of 30, my wood framed walls to R-13. If my house was built over a crawlspace the floor should be insulated to R-19. I've got a basement so that doesn't apply. My house was built in 1954 so truthfully none of these standards apply which is part of problem - why I am not comfortable in my house this winter.
R-value as you know means resistance to heat flow. So what does it take to meet these rather lax requirements for my zone 3 home? Here is a chart I've made showing various types of insulation with R-values.
You can make some broad generalizations that simplify the calculation for how much insulation you need. First wood has an R value of 1per inch and that makes up 25% of your wall. Second, most fibrous insulation (that includes cellulose, fiberglass, mineral wool, and denim) range from about 3-3.8/inch. No significant difference in R-values between them really. The foam materials roughly range from 4-6/inch in terms of effective insulation. So you pick either a fibrous insulation or a foam insulation and go from there. I'm anti-foam insulation for the most part so I would exclude that now. (Maybe another post some time down the road.) So to reach an R-13 wall, I need 3.7 inches of fibrous insulation which not coincidentally is about the space provided by a 3.5 inch stud wall. To reach my attic insulation requirement I need about 8.5 inches of insulation.
Where am I now in my cold little house? I had all new vinyl windows installed about 10 years ago, then about 5 years ago I had my house covered in 2 inches of polyisocyanurate foam for a R-10 continuous layer on my walls and new siding over that. What I have not done is insulate my attic because I have a leak around my chimney despite having it "fixed" about 4-5 times and I may to have to take a ceiling down when I renovate my kitchen. The R-value of the compressed fiberglass batts that do not cover the entire floor of the attic might be 6-8 at most. That's where most of my heat goes. That is the main reason I am in fleece long johns, wool socks, multiple sweaters and still cold despite the heat pump running constantly.
This house was built to code in its day. When energy was cheap, you just ran "Old Bessie", the ancient old heater (since replaced) constantly and kept warm. That doesn't work today and it won't work for the future. We have to do better with our houses. We will be happier, more comfortable, and have healthier places to live if we think past code minimums.