Does Zip Sheathing Require Outer Insulation in Canada
Hi,
I was in communication with Huberwood to find out where in Ottawa, Canada I can purchase Zip sheathing and their tape to price it out for my project.
I was surprised when I was told that regular Zip sheathing cannot be use on its own without outboard insulation on top in Canada. Not only have I never heard if this but their own R-Sheathing doesn’t even have the outer insulation.
Is the Huberwood sale rep mistaken or is this really the case in Canada?
E-mail communication with Huberwood sale rep:
From: Huberwood
Are you adding outboard insulation on top of the sheathing? The ZIP regular panel cannot be used on it’s own it need to have outboard insulation on top.
Thanks!
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From: Me (Arnold)
Hi Robert,
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From: Huberwood
Yes it’s a little complicated to explain on how they are testing products in Canada but with the assembly you are mentioning it’s good. The best place would Fransyl in Ottawa and they are also an EPS manufacturer.
Thank you,
Arnold
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Replies
I don't know about Canadian regulations, but regular Zip with no exterior insulation in Z5-Z7 needs a well sealed, Class I vapor barrier on the interior side. Such a Class I isn't a good idea where AC is used. Compare to plywood that allows enough moisture flow-through for a Class II in Z5 and Z6.
Yes, this is complicated to explain - especially if you don't want to say "Zip can create a moisture problem".
https://www.appliedbuildingtech.com/system/files/200311_abtg_rr_1701-01_moisture_control_guidelines_figure_update_final.pdf
Arnold,
Each province enacts energy requirements for building assemblies in their building codes, and often separate ones for the differing climates within their jurisdictions. That's what should govern whether a wall needs exterior insulation, not whether ZIP is used as the sheathing.
The Huber rep seems to imply it it has something to do with the testing and approval they went for. Maybe there is something specific to ZIP's approval process the necessities foam, but it seems unlikely.
I think Ottawa falls under zone2, so in that case no matter which compliance package you pick, exterior rigid insulation is required (between R5 to R10). So the zip rep is correct, you can't use Zip by itself as your assembly must have continuous exterior insulation. You certainly can use Zip with sufficient amount of rigid mineral wool or foam over it.
You can use Zip R by itself if you don't want to deal with the exterior rigid.
There is a generic REQUIREMENT for exterior rigid insulation on buildings in Ottawa???? I'm not a builder but I've never heard of such a thing. I think something is a bit weird here. I'm also stupefied that somebody (especially a Huber rep) said you can't use zip without exterior insulation in this climate. As long as you have an appropriately detailed rainscreen I can't believe this is true. There is absolutely nothing in the installation manual to indicate this. Somebody please clear this up!
http://www.mah.gov.on.ca/AssetFactory.aspx?did=15947
Table 3.1.1.3.A (IP)
My reading of this is that you are OK (i.e. in compliance) with an effective R of 20.32 to 25.32 (depending on compliance package). This can be done without continuous insulation by using a deep stud wall (2x8+ dimension lumber or I-joists). If continuous insulation is used, it can be placed somewhere in the middle of the wall, e.g. double-stud construction. In either case, zip sheathing can be used on the exterior without any additional insulation on top.
Code typical has prescriptive and performance based options. Prescriptive is easy, just "build it this way", so most people tend to use it.
Performance option gives you many more options but also means extra design work. The walls you propose can and do certainly work, they are just not "standard".
I generally find 2x4 walls with thick exterior insulation to be a pretty low cost and robust assembly, so that is my go to. 2x8 is also a good option, although at current lumber prices it is a bit more expensive for assembly R value.
User...903,
So circling back to Arnold's original question: There is no secret requirement unique to Zip sheathing that means you have to use exterior insulation with it in Canada.
Thanks for clearing this up. This is my first really in-depth look at this part of the Ontario
Building Code. I have no idea how a person off the street (even someone like me who has done a lot of reading about energy-efficient building) can navigate this thing without help from an expert. I still don't really understand the difference between all the "compliance packages" -- it is not laid very intuitively.
Unfortunately recent code amendments here in BC have followed the same path. On one level they make sense in the they allow a variety of approaches and solutions, but they are obviously written by and for a specialized professional audience. Something I think codes should try and avoid.
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Just came across this conversation now and thought I would add my 2 cents for others in the future... many new buildings I see in Ontario use Compliance Package A1, Table 3.1.1.2.A, which only requires a nominal R22 (and no continuous insulation) for exterior above grade walls, which is just batts in a 2x6 wall (very little cellulose here).
Most of Ontario is "Zone 1", including Ottawa. Only "Northern" Ontario is Zone 2 (Sudbury, North Bay, Thunderbay, etc.)
J. Murray,
I'm not the familiar with theOntario Building Code. What does CL mean in that table? Is that continuous insulation?
Yes, it stands for continuous insulation. (It's an " i " not an " l ").
Thanks. I haven't lived in Ottawa for over thirty years. One of my friends who is an architect there told me all new houses now had exterior foam. It seems odd they would go that route if there was a compliance path which meant it wasn't necessary. Something else must be driving it?