Exterior foam insulation in zone 6
ultracrystal
| Posted in General Questions on
Hi there, first off I’d like to commend this site and its community. The abundance of information and involvement is quite impressive.
My wife and I are currently nearing the final stages of planning our house. We live in Ottawa, Ontario putting us climate zone 6. Ultimately, the Ontario Build Code prescribes many parts of our design including insulation.
With respect to insulation, I’ve spent many hours reading others’ questions and various articles on this site but feel that ultimately, reconciling the OBC against the modern best practices may be a challenge.
Today I am asking for some opinions on the insulation of above grade walls. In my jurisdiction, I have available to me the following insulation options for these walls as prescribed by the code:
– R22
– R19 + R5 ci
– R14 + R7.5 ci
– R22 + R5 ci
– R19 + R5 ci
– R22 + R5 ci
These are all minimum nominal R ratings. My point of contention here has to do with the continuous insulation. According to the article https://www.greenbuildingadvisor.com/article/calculating-the-minimum-thickness-of-rigid-foam-sheathing, which is often referenced throughout this site, any type of rigid foam in my zone on the outside less than R11.25 (2×6 construction) is a no go.
Our current design calls for R22 Rockwool batts + R5ci. I haven’t nailed down how the 5ci will be implemented yet and ultimately I am juggling between XPS, EPS and Comfortboard but if I have to achieve R11.25 I don’t think I can have a CI without incurring more costs for my foundation for additional width on account of the brick ledge.
Please note that we are required here to have a vapour barrier on the warm side of the insulation. So a typical wall cross section would be
-Drywall
-Vapour barrier
-Insulated studs
-Sheathing
-WRB
-CI
…
Am I missing misunderstanding something here? Is an R5 CI really an option where I live?
EDIT: I’ve attached the relevant code document which I refer to in my question for anyone interested.
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Replies
Avoid the endless confusion created by the linked article and use Table 3 of this one. Use some exterior insulation but avoid XPS (it's bad for the environment). Also avoid low exterior perms (which increases Winter condensation accumulation).
Thanks for the link. After reading more and more about the effects of XPS on the environment I've been shying away from that option.
Eric,
Here are some additional, useful links for you to read and consider.
https://www.buildingscience.com/documents/building-science-insights-newsletters/bsi-092-doubling-down%E2%80%94how-come-double-vapor-barriers
https://www.buildingscience.com/documents/guides-and-manuals/gm-guide-insulating-sheathing/view
+1 on the XPS story. XPS that is labeled R5 is only warranteed to be R4.5, and at full depletion of it's HFC blowing agents after several decades it's more likely to be R4.2-ish.
1.5" of rigid rock wool is ~R6, and HIGHLY vapor permeable (30+ perms):
https://cdn01.rockwool.com/siteassets/o2-rockwool/documentation/technical-data-sheets/residential/COMFORTBOARD-80-Non-Structural-Sheathing-Continuous-Insulation-Techdata.pdf?f=20181016101508
1.25" of Type-II EPS is about R5 and about 2-perms- more vapor permeable than dry half-inch OSB or CDX, not a strong impediment for drying to the exterior.
1" of graphite loaded EPS (any density) is about R5. Type-II runs about 2.5 perms, slightly more drying capacity, Type-VIII or Type-I would be even more vapor permeable.:
https://www.insulfoam.com/wp-content/uploads/2014/04/15000-Insulfoam-Platinum-Brochure_REV3-17.pdf
1" IKO's EnerAir polyiso is about R6, and specifed to be greater than 1 perm at any available thickness (up to 2").
https://www.iko.com/comm/technical_documents/ener-air-brochure-english/
What is “ci” as in 5 ci? Please remember that some of us readers are not extreme technophiles in the building trades. (Most of the rest of the jargon I was able to understand or figure out by context.)
Mark,
I think it stands for Continuous Insulation - but I'm just guessing.
It's continuous insulation. This is how it's referenced extensively in the code that I refer to. I'll attach the official code documentation I refer to for anyone interested.
If you are in Ottawa, sure looks like you are Climate Zone 7 (very cold), using our US CZ map. I think you need to be careful distinguishing between climate zone-tuned recommendations and code requirements for the US and Canada.
Peter
Based on https://www.greenbuildingadvisor.com/article/climate-zone-map-including-canada I am in 6 though getting close to 7.
If I was in 7 based on the article I reference in my original question I'd be at R-15 continuous insulation which simply becomes prohibitive both from cost and working with others in my region.
I agree that I need to be careful; I've just be taken aback by some comments/articles on this site about the downside of too little rigid foam sheathing. So I'm getting some perspective.
I think in zone 7 the total number of HDD must be between 5000 and 7000 and in zone 6 it must be between 4000 and 5000. According to these numbers, Ottawa is definitely in zone 6. See https://ottawa.weatherstats.ca/charts/hdd-yearly.html
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