Pro Clima vs. Tyvek Water-Resistive Barriers
arnoldk
| Posted in Green Products and Materials on
Hi,
I am building a double stud wall with 2″ of exterior ridge insulation in Ottawa, Canada.
I am planning on using 3/8″ plywood sheathing on the exterior 2×6 wall and tape the joints to make it my primary air barrier but I am not sure what tape I will use yet. Open to any suggestion.
On the exterior of the sheathing I will be installing a WRB, 2″ Rockwool Comfortboard, rainscreen and finally the LP Smartside lap siding.
On the exterior of the sheathing I will be installing a WRB, 2″ Rockwool Comfortboard, rainscreen and finally the LP Smartside lap siding.
Is it really worth paying for the Pro Clima Solitex Mento 1000 compared to the Tyvek Homewrap for the WRB? The Pro Clima Solitex Mento 1000 is two half time the cost in my area once you factor their Tescon Vana tape.
Thank you,
Arnold
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Replies
You can hear some expert opinions on these products on this episode of the BS* + Beer Show: Choosing and Using Water Resistive Barriers.
Thank Kiley. I had a listen to it this morning and there was some great information.
Arnold
Arnold,
3/8" sheet goods are a bear to work with, especially if you are taping them. They have almost no inherent stability, warp and don't hold fasteners. Going up to 7/16" or 1/2" makes a world of difference.
I prefer Tyvek Commercial as a h0use-wrap. It's very robust, has a good perm rating and lays flat easily.
Hi Malcolm,
I met to write 1/2" plywood and not 3/8" like I did in my post. I have thought about increasing the wall sheathing to 5/8" just like to roof sheathing but that's a $12 increase per sheath and I not sure it's worth the additional cost.
Arnold
Arnold,
Great. 5/8" is a nice upgrade 0n roofs, but a luxury on walls. I'd only go that way if I wasn't doing the work, and had lots of extra cash.
You have a double stud wall plus 2” of exterior comfort board?
That is correct which will give us approximately R-60 in the wall.
Arnold
Typically enough exterior insulation is used to prevent condensation on the sheathing. With such a high r value wall, 2” of rock wool won’t be enough. It is vapor permeable, so the wall can dry to the exterior. However, wouldn’t it be cheaper and easier to just add more insulation in between the walls to hit your r value target?
The reason for the exterior insulation is to minimize thermal bridging in certain key areas: the rim joist, roof truss, around the window/door but mostly the headers and at the slab.
Base an some calculations an engineer colleague my wife worked with did for us for free, the exterior insulation made a difference. I was initially thinking of not doing the exterior Rockwool Comfortboard to save on the cost but the engineer suggested we keep it.
- With 2" exterior insulation -
R-60: (62.925)
reduction R-value: 11.925
True wall assembly R-value reduced by 19%
- Without 2" exterior insulation -
R-52: (54.925)
Reduction R-value: 21.925
True wall assembly R-value reduced by 40%
Thank you,
Arnold
You might want to spend some time reading some articles on double stud walls like this one:
https://www.greenbuildingadvisor.com/article/a-case-for-double-stud-walls
https://www.greenbuildingadvisor.com/article/exterior-rigid-foam-on-double-stud-walls-is-a-no-no
I can’t see many situations where exterior insulation makes sense on a double stud wall.
I would check the math on that.
A 2x6+5.5"gap+2x4 double stud wall dense packed with cellulose gives you around an R52 assembly using R53.5 of insulation. With 2" exterior rigid, if you want the same assembly R value, drop the gap to 3.5". Both walls are almost the same thickness, the one with exterior rigid would probably be 2x the cost to build.
As for WRB, I would 2nd Malcolm. Tyvek commercial is a great product, sturdy and can be left exposed for 9 months. It also comes with an 8x8 grid printed on which makes installing strapping much easier. Worth the extra bit of cost. You can tape the seams of your sheathing with any of the quality tapes (Zip, 3m 8067, Tescon )
Normalize your numbers to $/whole-wall-R. Too many people get hung up on "I have to reduce thermal bridging".
Even better is a life-cycle ROI that looks at all the options. There are probably things that are better for the environment and better for your pocketbook than R60 walls.
Kyle:
The exterior insulation is Rockwool Comfortboard (mineral wool) which is vapor permeable. I am not using EPS or XPS foam as the exterior insulation so there wall assembly will be able to "breath" toward the interior and exterior.
Akos:
The wall assembly we're going with is 2"ridge insulation+2x6+3.5" gap+2x4 which will give us about R-60. I wasn't going to use the exterior Rockwool ridged insulation but after my wife's colleague provided us with his calculation, my wife was sold on it. She also did not want the wall thickness to increase beyond what we already had.
I have bigger fish to fry in this built than a few thousand of dollars of exterior insulation so I simply smiled and nodded. Happy wife, happy life.
Thank for Akos and Malcolm for your feedback on the tape and WRB. Tyvek and 3M 8067 was my initial thought and it's what I am using for the detached garage. I guess it's easy to over think the details when your neck deep in various product available to you.
Arnold
Arnold,
The wall is complicated to build but will be an excellent assembly, making a decision and going for usually saves more time than dithering.
The Tyvek I was talking about is not the standard home wrap that most places carry. You are looking for Commercial Wrap, which is a bit harder to source as only commercial building suppliers carry it. Make sure they understand it is not home wrap, as I've had the wrong one shipped to me before.
I don't know about Ontario, but in Quebec you need a layer of continuous exterior insulation of at least R4. I suppose you have some sort of similar requirement in Ontario. If that's the case, the rockwool layer is not optional and will be required.
*I think R5 is required in Ontario according to OBC 2017 but could be wrong.
I believe you correct but I am not sure if that would apply to double stud walls or not. I never looked into it because my wall assembly excided OBC requirements.
Arnold
Another option since you are close to Quebec would be to use Eco4 SONOclimat wood fiber boards instead of Rockwool. It's sold in Canac stores. It's more ridgid and easier to detail than rockwool but the insulation value is only R4, which might be not enough in your case. It could probably replace your plywood layer as well if you combine it with some metal wind braces.
The cost is not too bad 0.75/sqft before the pandemic but like everything else right now, there is a shortage and the prices are a bit higher.
Another option and the one I'm planning to use on my house is a double stud wall with the eco 4 on the outside and osb on the inside. You install a membrane on top of the eco 4 and tape the interior osb. This way the eco 4 acts as a water/air barrier and the interior osb play the role of an air/semi permeable vapor barrier.
Alex,
I'm hoping to start building next spring and was planning to use the eco4. Is there a shortage of msl products? I was hoping the local manufacturing would help me avoid supply chain issues.
I was also under the impression that double stud wall may not be required to have outside insulation since they have thermal break already.
Regarding your wall, are you confident you'll be able to convince the inspector to forgo the poly or foil-faced board on the warm side?
I don't know if there is a big shortgage but Canac has nothing left in stock at the moment (one store has some 4x9 panels but that's it).
I don't know about the thermal break. Never thought about it since I was going to add an eco4 layer anyway.
Yeah the poly can be a problem. You can argue that a 3/4 OSB panel is a good enough vapor barrier according to the building code because the permeability is less than 1 perm. The other option and the one I will probably use is 1/2 OSB painted with a vapor permeable primer. Check this article for more details https://www.ecohome.net/guides/2299/painting-on-your-vapour-barrier/
We don't have mandatory inspections here so I should be fine. If someone insists that I add a membrane, I'll probably use something like Proclima Intello.
Alex,
Doesn't going with OSB put you into that same grey zone that a variable perm membrane does?
OSB is between 1 and 2 perms when dry, but opens up to 12 when wet. I don't see any language in the code section that allows it to vary above the prescribed limit.
I'm not that familiar with the Ontario building code, but I seem to recall from past discussions here that there is an alternate path to compliance for thick walls so that external insulation isn't necessary.
I did look into using Eco4 but decided to use Rockwool Comfortboard instead. I also have half of what I need stored in my garage but the rest I should get in November.
There seems to be a shortage of Comfortboard as well which is why I went to two different store to purchase what they already have an found another store who can get the rest for me. Most store I spoke to said they were told any order place in now wouldn't arrive until at least spring 2022.
Originally I was going to use BP Can Excel II insulated structural sheathing on the inside of the 21x6 wall. The issue I ran into is no one really knew anything about it and it would be at least 10 weeks before they could get the product in. No price was given despite asking a few times so I suspect it on the expensive side no the distributer doesn't have any update pricing.
The other issue is having to us bracing when building the wall in order to square them off before lifting them up in place. Since I am not going to be doing the framing over the winter, I decided to keep things simple with tried and true products and use plywood on the exterior which will also be my primary air barrier.
I have realized in the last couple of months that you can easily go down the rabbit hole and over think think and complicate thing. My wall assembly with the exterior insulation may be over kill but it's what we decided on for various reason. We're also wrapping up our building permit process so any changes will simple add even further delays than we have already experienced.
Arnold
Hello Malcolm
According to Quebec building code and most Canadian codes I suppose :
Vapour barriers shall have a permeance not greater than 60 ng/(Pa·s·m2) measured in accordance with ASTM E 96/E 96M, “Water Vapor Transmission of
Materials,” using the desiccant method (dry cup).
So it doesn't matter if the permeance vary as long as the permeance in a dry cup test is under 1 perm. The wet cup permeance doesn't matter.
For instance, Intello permeability is 0.2 perm when dry so it is compliant.
https://foursevenfive.com/content/product/air_sealing_system/intello_plus/spec_sheet_intello_plus.pdf
Alex,
That's good to know. Inspectors here have been reticent to approve variable perm materials as vapour barriers, but there doesn't appear to be any code backing for that stance.
My biggest concern with intello and other smart membranes is we don't know what they will look like in 50 or 100 years. We should use material that we know will last as long as the house itself. Will intello+ look like the kraft paper on the fiberglass batts in my 50 year-old house that's just disintegrating?
I'm leaning toward using foil-faced board (eps, polyiso or fiberboard) for the vapor barrier (and air barrier) on my double stud wall. My wall will be vapor open to the outside with rockwoll, eco4 and high perm wrb.