How to get an R60 roof with closed cell spray foam?
jobphoto
| Posted in Energy, Heating & Insulation on
We are going to build a new home in a year and a half, and am still in the design stage. We live in Southern Ontario, Canada, (in other words – a cold climate). Current new homes are required to have an R50 roof insulation here, and because I know that will change in time, I want to build with an R60 level, using closed cell spray foam – I’ve had some experience with it in a renovation I did last year. However it appears that it reaches it’s maximum R value at about 5-6 inches which equals approx. R30-36. I know it is also a superior air barrier, but I want to get as high an R value as I can. Any suggestions – without breaking the bank?
Replies
do you have an attic ?
with an attic it's fairly easy to get r60....say 17" - 18 " of cellulose
I suggest you go to Joe Lsturbeck's website: http://www.buildingscience.com/doctypes/designs-that-work
and digest everything Joe, who hails from Toronto, has to say about this.
Joe has "written the book" on this topic. Most of us here have a little hands-on experience with two or three methods, but Joe is the pro voice you need to listen to.
JobPhoto,
It is untrue that spray foam insulation "reaches its maximum R-value at about 5-6 inches which equals approx. R 30-36."
R-value increases with depth. To achieve R-60 with closed-cell spray polyurethane foam, you need about 9 or 9 1/2 inches.
Martin Holladay, senior editor
http://www.greenbuildingadvisor.com
Thanks for the reply Martin.
I got that info from a PDF that I downloaded from the FHB website, which compared open and closed cell spray foam properties - written by ROB YAGID, so I guess the question is - who is right?
Cheers, Jobphoto
Job, I think they are both right. For most of us we have reached our maximum gain at 5-6 inches and addtional R Value above that is a waste, but in your area to get the R60 that you need you are justified in adding the extra inches. In a warmer climate the diminishing returns on the higher R value don't justify the expense, but perhaps in your area it does.
The more depth of foam or any kind of insualtive amterial you apply propewrly, the more R-value you gain.
The idea that spray faom does not gain R-value is a miscconception based on nmis-understanding studies and experience showing that dollar value falls off perceptively after you have 5-6" applied.
In simpler words, you do gain resistance to heat loss with greater depth, but it does not do you much good from a cost/value POV
Do what we did I joist rafters for the roof, you can go as BIG or small as you want. We managed to get R90 in our roof super easy. https://honeybramble.com/home-interior-design/building-your-own-house-from-the-ground-up/ Yes, we used Rockwool instead of spray foam, but you could easily switch to whatever flavor of insulation you like the best.