Friday, July 30, 2010

Insulation: There is more than just the pink stuff

Insulation.... ahh the sexiest of home renovation topics. Alright, it can't compete with cabinets or flooring. Heck even faucets look exciting in comparison, but when it comes to a green renovation, insulation along with sealing your home envelope are the meat and potatoes.

With insulation, it all comes down to R-value. R-value is essentially the “Thermal Resistance” of a material. The higher the number the harder it is for heat to pass through. Seeing as this is the job of insulation, R-value along with price are usually the deciding factors in picking your insulation.

There was a period when fiberglass insulation was the beginning and the end of your home insulation choices. Nowadays, it is part of a subcategory. The list below is by no means exhaustive, but it covers what we felt were viable insulation options for our project. If you really want details there is a pretty good insulation guide put out by Natural Resources Canada.

Batt insulation: flexible insulation that fits between the wall studs. This includes traditional fiberglass but also the awesomeness of Roxul. Its easy to install and typically the least expensive.

Spray foam: A spray on insulation that provides not only some of the best insulating power per inch but also acts as an excellent air/vapor barrier. Can be expensive and for any significant job requires an outside contractor. Small jobs can be done by DIYers like we did behind the fireplace.

Rigid Insulation: Rigid foam panels. Again increased R-value and eliminates thermal bridging but can be expensive.

Now, if you didn’t catch it above, I am a fan of Roxul. So much so that it makes me wonder why you still see so much pink stuff in Home Depot’s aisles (Roxul is green). Roxul is made from stone wool: essentially rock and recycled slag spun into fibres. The result is a product that is:
  • Easy to handle, cut and install

  • Offers great R-value: R-14 vs. R-12 for fiberglass (although in writing this I have discovered both a new Roxul and new fibreglass rated to R-15)
  • FIREPROOF! (it is rock after all, and I guess officially it is only fire-resistant as it will melt at 2200 degrees F)

  • Made from 40% recycled material
  • Minimal additives, no off-gassing, etc

But for our project we needed more than just Roxul. For LEED certification we needed a minimum of R-20. Since our exterior walls are 2X4 construction we identified three options to get us over R-20:

Option 1: Spray insulation between the studs: R-24.5
Option 2: Build up the wall 2” and use 2x6 Roxul: R-22
Option 3: Use Roxul in between the 2x4s and add 2” of rigid insulation: R-24

While they all seem to be in the same ball park performance wise, the R-values above are just for the insulation and do not account for a phenomenon called “Thermal Bridging” . Say you build a beautiful 2x4 wall and have it all nicely insulated with R-24.5 spray foam. That is great but the wood studs conduct heat too and they only have an R-rating of 4. So they act as a “bridge” for the heat to pass through. If you take this into consideration then the R-value for the wall is: 17.1 (I will not bore you with the equations). Looking at the R-values for the wall, the revised numbers become:

Option 1: R-17.1
Option 2: R-19.5
Option 3: R-22.6

Option 3 has the rigid insulation that covers the studs and thereby eliminates part of the thermal bridging explaining why it performs better. The above calculations also are for standard framing (a stud every 16”), if you were to account for all the extra lumber around the windows and doors the performance gap between Option 3 and the others would get even bigger.

Wow…that was a very long lead into to explain that we are using R-14 Roxul with 2” Styrofoam on top:

First step was to cut and fit Roxul into all stud openings. It cuts great with any serrated knife (just don't tell Jody that I used one of our good kitchen knifes).

Electrical boxes neede to offset 2" to account for rigid installation. They also need vapour boxes around them with electrical connections taped off. This prevents air and moisture from passing through the box. It is also the reason most older homes have drafts through the outlets in the winter time.

The rigid insuation is then intalled.
It is screwed on to the studs using recessed washers. Then all the vapour boxes are sealed and taped flush with the styrofoam.

So what does the mean for our LEED points: nothing really yet… First off we have only insulated 10% of our house so we haven’t met any criteria yet. And we do not get points for the insulation itself but rather the overall efficiency rating of the house (which is big points: up to 28 but we are hoping for 10). When complete, we are also hoping to get a half point for recycled content in the insulation.


  1. Interesting stuff man – I'll definitely be referencing some of the things you've been referencing when I tackle our basement!

    I'm surprised you didn't *bore* us with the bridging equation ;-)

  2. The next time I have a house built. I am going to get you to be my inspector. Boy you sure are into a lot of detail. Great work.

  3. @Ken: I try hard not to let my geeky engineering side come through on the blog.

  4. have you checked out Roxul Drainboard... its a great product, cheaper than styrofoam and R4.3/inch :) Yay for Roxul

  5. I'm very glad i found this blog, while hunting references to recycled-glass countertops. And I'm glad I read this post before I skipped over to the hardware store for pink batts, for my diy laundry-room reno. I'll definitely look for Roxul. And thanks for the info on wood studs bridging - I didn't know that; but it makes me extra glad I planned on using rigid insulation against the concrete first.
    It's pretty awesome to have bumped into a green reno blogger who happens to live just North-East of me. I had a good laugh when I recognized the map of the area. All the possible endpoints the internet could have taken me...and i end up in my neighborhood.

  6. Great post given by this site to renovate the small idea about the Foaming agent in commercial point of view.This implement the price effective way to develope well insulated concrete..

  7. What did you do around the windows?

    1. As you can see from the picture, I installed the rigid insulation over the window framing and up to the sill. I then trimmed a finished board to the right thickness and extended the sill to be flush with the drywall. Filled and sanded the gap and after paint it looked good. Also used great stuff between the rigid and the sill to seal it.

  8. I'm glad to hear more people talking up the benefits of the Roxul products. I think one reason for the lack of awareness is that its not on the shelves. If I want Roxul, I have to make a special order with customer service at Lowes or Home Depot.

    1. No Lowes in Quebec but lucky for us both the Home Depot and Reno Depot carry it here.

    2. This is a great idea. I was considering something similar to account for thermal bridging, but I don't see how the drywall attaches once you add the rigid foam. Also, did you add a moisture or vapor barrier? Thanks.

  9. Thanks for the great detailed writeup and pictures. I'm starting a den extension insulation project and just bought a bag of Roxul R-14 and reading your write up really inspired me!

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