Best exterior wall design within standard 2×8 dimensions
I have been reading several of the GBA posts and articles and I don’t seem to locate the answer to my question so I wanted to drop you a line by email.
I am located in Saskatchewan, Canada and currently have a house under construction that is well under way. That being said I won’t over complicate it with detail but the house is not a high efficiency design and I am not and don’t pretend to be knowledgeable on a lot of points that are covered on GBA.
Hhowever, this is what i have
Southeast corner of Saskatchewan, Canada 15 miles north of North Dakota
2000 sq ft per floor – main floor and partial walk out (south side walk out)
ICF 8” insulated concrete basement walls
House is south oriented with high SGHC glazing on all windows, although there is very minimal north facing and only one west facing windows, the south glazing is approximately 50% of the south wall sq ft with overall glazing approx. 20% of exterior wall sq ft
Back to the question(s):
The situation I am in is i recently discovered the GBA wealth of knowledge and the basement is already constructed with main floor framing ready to commence.
Because of this I am limited to the 2×8” framing wall thickness for the main floor
The construction originally called for 2×6 walls, which was altered because I was wanting more insulation value I opted to go to 2×8 exterior walls.
However, now after much reading of your very informative articles I am posing the following question:
Would I be better to go with a double 2×4 stud with offset studs to help reduce thermal break?
They typically insulate the 2×8 with a R22 fiberglass batt, reading your posts would you recommend a cellulose blow in and what method would you recommend?
I have discussed with the contractor regarding cellulose and he says they use the fiberglass batts as the fiberglass has better air flow at the same R value.
Isn’t he wrong in his thinking here? His concern is vapor in the wall assembly without sufficient airflow within the wall.
From your site, I am lead to believe this is poor theory but reading comments and posts I am unable to determine what the right answer is, other than cellulose is better but why?
Current construction design if i don’t intervene
2×8 framing with 6mil poly air barrier, R22 fiberglass batts, 7/16 exterior OSB sheathing, Tyvek regular house wrap, James Hardie siding
My suggested alternative
2×4 double framing on 2×8 plate with offset 2×4 to eliminate thermal bridging, 6mil poly air barrier, cellulose blow in insulation (what method to use?), 7/16 exterior OSB sheathing, (or is there a better alternative?) exterior foam with taped joints, suggesting this product http://buildwithhalo.com/# but what thickness to use for foam? , James Hardie siding
I was also trying to determine your installation recommendation for windows, I plan to use triple pane units with glazing spec’s like cardinal glass has on their LoE180 on 2 surfaces, with argon in both spaces. These will be European units and I am awaiting a few quote details to finalize what brand I am going with. Most builders in this area only know to install nailing flange windows that they pound up and spray foam the inside and done. I thought I saw references to an install guide Martin Holliday had online for installing high efficient windows into foam sheeted walls but can’t locate it….
So virtually my question is really two questions:
With my 2×8 wall thickness framing constraint in mind, what in your (GBA) opinion is my “best” wall construction method and with what materials?
Do you have a window installation best practice guide you can share or have the link?
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