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: 5797

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.

Photos

Loading…
  • Add Photos
  • View All

Latest Activity

Profile IconCharlie Ouellette, Karin Haerter and Juan joined Home Energy Pros
8 hours ago
Juan added a discussion to the group Energy Auditing Equipment for Sale, Trade or to Purchase
Thumbnail

Need Energy conservatory Blower door 3 + DG-700

Hello thanks for taking the time to read this post. I am currently looking for a blower door…See More
9 hours ago
Juan joined allen p tanner's group
Thumbnail

Energy Auditing Equipment for Sale, Trade or to Purchase

Discuss the pros and cons of the equipment you are interested in prior to purchase. Post equipment…See More
9 hours ago
Caoimhin P Connell replied to Rodney Fox's discussion Radon: Truth vs. Myth
"Good morning, Mr. Cullen – As I mentioned in another post – for the purposes under…"
10 hours ago
tedkidd replied to Rodney Fox's discussion Radon: Truth vs. Myth
"If putting the house under positive pressure using fresh air helps mitigate not just radon, but…"
11 hours ago
Rich Manning replied to Rodney Fox's discussion Radon: Truth vs. Myth
"Tell them the truth as you know it, and back it up with the facts!!"
11 hours ago
Rich Manning replied to Charles Ryan Weitzel's discussion Oil Fired Boiler Being Used as the Heating Source in Two Air Handlers of a Historic Home
"Yes, its a Hydro-air system. It uses one boiler to supply hot water to the coil in the supply side…"
12 hours ago
tedkidd replied to Rodney Fox's discussion Radon: Truth vs. Myth
";) I love uncovering absuedities... Funny how creatively and vehemently people will argue against…"
12 hours ago

© 2016   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service