Author Note: Here's
 a link to the original post on
 Energy Auditing Blog.

Besides the obvious answer - MORE (but you knew that just based on your heating bills, didn't you?), how much insulation do you need? There are loads of different standards from Energy Star to PassivHaus to your dad ("about this much" ... holds hands apart).

The whole deal rests on the vagueness of the concept of 'enough' insulation. Without much effort, I also recalled current building code standards, International Energy Code, the oh so vague 'super-insulation'... there are a load of different measures. So which one is 'correct' and how much insulation do you need?

Right off let me say there is no objective standard for insulation levels and none of them are 'correct'. I can't even type the word correct in this context without envisioning fingered 'air quotes'. Insulation level recommendations are based on climate zones, energy models and most importantly, extensive real world observation actual energy use and costs. When smart people have loads of controlled data they can draw some pretty good conclusions but not objectively correct ones.

What we can do is find some reasonable yardsticks and a reliable one is the '10 20 40 60' insulation guidelines by Joe Lstiburek of Building Science (If you haven't been to their site, Building Science is the catnip of energy pros). These guidelines call for an R-value of R-10 sub-slab insulation, R-20 basement walls, R-40 building frame walls and R-60 attic insulation anywhere north of the Mason-Dixon line.

Sub-Slab - XPS foam board is the most commonly used sub-slab insulation. R-10 equals 2 inches of XPS foam. If you have a full basement and the slab is not insulated (very likely), insulation can be laid down and a new slab poured. Granted this is a larger project; you will have to move all your college text books.

The Foundation Wall - The foundation wall should be insulated to an R-20. If you've not blessed with the fortune of having an insulating concrete foam (ICF) foundation, there are a few other options. Insulating the exterior is possible but carries a number of limitations (described in this article on basement insulation). Insulating the interior can be done with 2 inches of XPS or closed cell spray foam then framed with a 2 x 4 studs. Add any standard insulation to the stud wall will help reach R-20.

Building Walls - R-40 ... that's a lot of R's! More importantly, the approaches that can achieve this fix thermal bridging issues. Structural Insulated Panels (SIPs) that are sufficiently thick or standard 2 x 6 framing with 4 inches of exterior polyisocyanurate foam board can achieve R-40 insulation. In retrofit situations, polyisocyanurate is typically added to the exterior.

Note: I'll pause here to mention that the insulation approaches should be taken with a few trainloads of salt. There are MANY different ways to achieve appreciable higher insulation levels in basements, walls and attics.

Attics and Ceilings - R-60? What? Now I've just gone loopy. Before I get into the insulation ... air sealing. The attic flat must be absolutely air sealed for the insulation to work. Once the air barrier is sealed, R-60 can be achieved with 2 layers of 12-inch fiberglass cross batts or 20 inches of blown cellulose (allowing for settling).

If you have a cathedral ceiling, you'll have a steeper haul. These roof usually require 6 inches or more of exterior foam sheathing to reach R-60.
There is no correct guideline for how much insulation you need to install. You can reach a point of diminishing returns. I mean how much energy would you save going from R-60 to say R-100? Very little.
OK, I'll give in...here's a link to the Department of Energy's very cool Insulation by Zip Code lookup tool and a chart on current insulation recommendations by climate zone.

Department of Energy Insulation map by climate zone

Views: 2806

Comment

You need to be a member of Home Energy Pros to add comments!

Join Home Energy Pros

Comment by Lee Price on July 11, 2012 at 7:21am

The best way to determine what level of home insulation you need, at least in the UK, is to have a surveyor come in and inspect your house for you. Climate levels are less of a concern over here as they are pretty much universal, so a surveyor can generally give a pretty good idea of what's required.

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Kari Sauder replied to James White's discussion What happened to Home Energy Pro's website?
"I stopped using Firefox -- too many glitches"
1 hour ago
Hal Skinner replied to Hal Skinner's discussion How our ceramic based RCC works in the group Radiant Control Coatings
"Hey Tom, I will find the ORNL repoprt and post it.  It was a test on a ballasted roof sample.…"
9 hours ago
Tom Mallard replied to Hal Skinner's discussion How our ceramic based RCC works in the group Radiant Control Coatings
"So it seems that what you're saying is for heat-transfer the stuff has little resistance or…"
10 hours ago
Hal Skinner added a discussion to the group Radiant Control Coatings
Thumbnail

How our ceramic based RCC works

How our RCC worksEveryone knows, understands and accepts that RCCs reflect heat away from roofs,…See More
11 hours ago
Mike Kandel posted a discussion

Earn BPI CEUs at 3rd Annual Building Performance Forum

If you're searching for BPI CEUs, you'll find plenty at the 3rd Annual Building Performance Forum…See More
16 hours ago
Mike Kandel added a discussion to the group Building Performance Institute (BPI)
Thumbnail

Earn BPI CEUs at 3rd Annual Building Performance Forum

If you're searching for BPI CEUs, you'll find plenty at the 3rd Annual Building Performance Forum…See More
16 hours ago
Sean Lintow Sr commented on Christopher Morin's blog post UPDATED: Big Changes for Duct Testing in MA
"4% TOTAL Ted - Leakage to outside was stripped from the codes & for good reason"
19 hours ago
tedkidd commented on Christopher Morin's blog post UPDATED: Big Changes for Duct Testing in MA
"Wait!  4% total leakage or 4% leakage to outdoors? "
20 hours ago

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service