XPS/Cellulose Remodel in Winnipeg – HELP please! :)
Hi everyone,
I’ve read a LOT of threads here and I’m actually overwhelmed. I have 10 tabs of GreenBuildingAdvisor open and I feel like my brain is going to explode. So I am just going to ask… Thanks in advance for reading my post.
First off, I’ve seen Riversong and JKLingel, Gary Bergeron, Martin Holladay, and Peter Yost making lots of awesome posts and articles on this site; and I’ve been awed by the stuff Joseph Lstiburek has over at BSC. Thank you all tremendously for your dedication!
I’m hoping anyone can advise on our remodel of a 900sqft bungalow in Winnipeg, Manitoba, Canada. I’ve read pretty much everything that Lstiburek and the CCHRC in Alaska have written on the subject, and tons here at GBA, but I’m still unsure what to do. We are really trying to keep the total costs down with near-term payback in mind. I really appreciate anyone that could take the time to address some of my questions!!!
-We plan to gut the 2×4 walls and strip off the existing stucco.
-Replace cavity insulation with either “BIBS” (Mooney Wall http://www.builditsolar.com/Projects…MoreMooney.htm) dense pack OR blown wet cellulose.
-On the outside, add a minimum 2″ of XPS sheeting over plywood or MDF. I’d like to avoid putting more than 2″ because of the obvious window jam-extension issues, but if condensation inside the cavity wall could be a problem, then maybe I must. Obviously, it gets extremely cold in Winnipeg but it’s also very dry and I will be properly using my HRV to keep humidity down towards exterior levels. Mould is not generally a problem here.
–As an alternative, perhaps Roxul CavityRock or Thermafiber. I don’t know much about it yet.
-Either DrainWrap or House Wrap over the XPS. Apparently vinyl is leaky so which is better? (If I go with drainwrap then I don’t need furring strips which would be nice in terms of thickness.)
-Finally – “0.50 profile” thick vinyl siding or Mitten Insulplank Fullback Insulated Siding. (I’ll be looking for the 25′ long pieces I read about in FHB this month.)
Questions:
1) Do I need to put MORE than 2″ of XPS to avoid condensation and mold? This article refers: http://www.cchrc.org/docs/snapshots/…Insulation.pdf Can WUFI answer this?
2) Which is most cost effective and best for ‘new-construction’ type remodelling – blown wet or dense-pack cellulose? What about “settling issues?”
3) Do I need to limit the amount of cellulose I put in the cavity if I only use 2″ of XPS?
4) Can I skip the poly vapour barrier inside and only use airtight drywall + latex paint (Benjamin Moore Natura Interior Primer.) We aren’t intending to add air conditioning at this point, but the next owners might so I don’t want them to have mold problems from the A/C and the wall not breathing.
My biggest concern is that since the “airtight drywall” and paint is a vapour retarder, and so is the 2+” XPS, isn’t this creating a double vapour barrier? Would polyiso be better or worse?
Thanks everyone and anyone who could tackle some of these mind-bogglers.
If you’re interested, I’ve got photos, floorplans etc on my blog at http://adreamhome.wordpress.com/
Also, I’ve done a mountain of research on cool housing technologies and you can find it all in my social bookmarks at http://www.diigo.com/list/scriptures…_fs-insulation
Cheers & thanks so much!
Danny Vanderbyl
Winnipeg, MB
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Related Threads:
-https://www.greenbuildingadvisor.com/blogs/dept/musings/calculating-minimum-thickness-rigid-foam-sheathing
-https://www.greenbuildingadvisor.com/blogs/dept/musings/are-dew-point-calculations-really-necessary
-https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/16378/temperature-change-through-exterior-wall
-https://www.greenbuildingadvisor.com/video-superinsulating-home-rigid-foam
-https://www.greenbuildingadvisor.com/community/forum/green-building-techniques/18650/alternative-non-foam-outsulation-strategy-using-rock
-https://www.greenbuildingadvisor.com/blogs/dept/building-science/vapor-profiles-help-predict-whether-wall-can-dry
-https://www.greenbuildingadvisor.com/blogs/dept/musings/getting-insulation-out-your-walls-and-ceilings
-https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/15208/explain-correct-usage-rigid-insulation-exteri
-https://www.greenbuildingadvisor.com/blogs/dept/musings/how-risky-cold-osb-wall-sheathing
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Replies
Danny,
Q. "Do I need to put MORE than 2" of XPS to avoid condensation and mold?"
A. Two inches is good enough for a 2x4 wall, but if you strap the interior of the wall and make it the equivalent of a 2x6 wall, you need 3 inches of XPS. For more information, see: Calculating the Minimum Thickness of Rigid Foam Sheathing.
Q. "Which is most cost effective and best for 'new-construction' type remodelling - blown wet or dense-pack cellulose? What about settling issues?"
A. Either one will work. Installed by a contractor who knows what he or she is doing, neither will settle.
Q. "Do I need to limit the amount of cellulose I put in the cavity if I only use 2" of cellulose?"
A. I don't understand the question. Two inches isn't much. What do you mean by "limit"?
Q. "Can I skip the poly vapor barrier inside and only use airtight drywall + latex paint (Benjamin Moore Natura Interior Primer.)?"
A. Yes.
Q. "My biggest concern is that since the "airtight drywall" and paint is a vapour retarder, and so is the 2+" XPS, isn't this creating a double vapour barrier?"
A. The wall will be able to dry to the interior, through the paint. Don't worry.
Q. "Either DrainWrap or House Wrap over the XPS. Apparently vinyl is leaky so which is better?"
A. Ordinary housewrap is all you need under vinyl.
Q. "If I go with drainwrap then I don't need furring strips."
A. The furring strips are still handy -- so that you can nail the siding to the furring strips.
Q. "0.50 profile thick vinyl siding or Mitten Insulplank Fullback Insulated Siding?"
A. Forget the Fullback siding. It doesn't drain as well as regular siding, and after all you already have foam sheathing..
Thank you very much Martin! I really appreciate all your responses and the work you and everyone is doing here at GBA!
In my question I meant to ask - if I use only 2 inches of XPS - will I need to reduce the amount of cellulose in the cavity or can I pack it tight? (Ref the CCHRC article - do I need to keep more than 50% of the wall's insulation outside the cavity in order to avoid mould?)
One other question - can anyone comment on using Roxul or Thermafiber in lieu of XPS sheeting as outsulation?
Overall I am tremendously reassured and I will pass your comments on to my contractor.
I hope that anyone else pursing a high-insulation / low cost strategy is helped by this research and Martin's comments.
Once again thanks so much!
Danny
Danny,
Q. "If I use only 2 inches of XPS, will I need to reduce the amount of cellulose in the cavity or can I pack it tight?"
A. In a wall cavity, cellulose should always be installed using the dense-pack method. The installer should aim for a minimum density of 3.5 pounds per cubic foot. If your wall is a 2x4 wall filled with dense-packed cellulose, then 2 inches of XPS sheathing (R-10) will be thick enough to keep your wall safe in Climate Zone 8 or any climate zone that is warmer.
Q. "Can anyone comment on using Roxul or Thermafiber in lieu of XPS sheeting as outsulation?"
A. The basic problem with Roxul on the exterior side of your sheathing is that it is not dense enough to resist compression when attaching vertical furring strips with screws, so you need to devise some type of sleeve for your screws, or use special double-threaded screws, to keep your furring strips co-planar.
You can search the GBA Web site to learn a lot more on the topic. For example, see these three threads:
https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/17899/vapor-open-rigid-foam-insulation-exterior?page=1
https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/19969/apples-turds-mineral-wool
https://www.greenbuildingadvisor.com/community/forum/green-building-techniques/18650/alternative-non-foam-outsulation-strategy-using-rock