I am building an addtion (20 feet by 10 feet) with an 8 foot deep basement attached to the house. I live in toronto Ontario, very cold winters. I want to know if what i want to do is gonna work.
Usual construction=
2×6 wall
osb sheathing,
tyvek outside of exterior osb sheathing, then siding (either vinyl or brick),
on the inside use roxul (mineral wool insulation) in between the studs (24 o.c. or 16 o.c. still have not decided),
6 mil vapour barrier,
then drywall (1/2″), prime, and paint (all latex).
This is typical for the where i live.
I want to do this: I have read about the REMOTE or PERSIST method of wall construction.
2×6 wall,
osb sheathing (glued to studs with pl 400 or pl premium -every seam)- this makes the assembly stronger and more airtight,
forget tyvek, i want to use ice and water shield on the exterior sheating rolling it so it adhears better (like the PERSISt and REMOTE methods). I am hoping to make the addition less air leaky, and if water ever hits the ice and watershield, it will just run off.
roxul (mineral wool the stud cavities
NO INTERIOR vapour barrier of any kind
1/2 drywall
prime and paint with latex?
what do you guys think.
Basically it is taking the housewrap (exterior) and interior vapour barrier (6 mil) and eliminating them. And installing Ice and water shield on the exterior. That way the exterior does not get wet, and if it does, it can dry to the interior. NO FOAM ON THE EXTERIOR OF ANY KIND.!
THanks
Replies
Toronto doesn't get as cold as it does here, but still cold enough that I don't think that's a good idea. With no interior VB and the IWS on the outside you will trap moisture on the cold side of the wall, causing severe condensation.
The key to REMOTE (Residential Exterior Membrane Outside Insulation Technique) seems to be the insulation on the exterior face of the outside vapor barrier, but you make no mention of that. In the instuction diagram here (http://www.cchrc.org/remote-wall-study) they show 4"-6" of foam over the OSB.
What is your foam detail?
In a primary heating climate moisture will drive from the warm side (interior) to the cold side of the building envelope. The vp on the inside is to reduce the amount of moisture that will be driven into the wall cavity, where it will condense on the cold side of the wall.
It will not dry to the inside until the following spring when you turn on your a/c. By then you will have established a fair chance for rot and mold to be underway inside the walls.
Ice and water shield is just that. It is not permeable to any moisture movement through it at all. Tyvek and Typar are both proven weather barriers that allow moisture diffusion through them while providing the water resistance you are looking for.
IMO wraping your home in ice and water shield is like placing it in a big ziplock bag. Your normal living activities will create enough moisture durring heating months to start filling the bag up with condensate water.
If you do what you propose the house WILL have serious moisture problems very quickly. It's not even "might", but WILL.
cool
Thanks for the information. I guess i will have to do it the REMOTE or PERSIST way.
thanks for the replies.
I think it's a bad idea for reasons already stated by others.
I've never used mineral wool insulation but was reading a piece in JLC (I think) where they tested wall systems with fiberglass batts that had gaps as small as 1/4" next to the stud. They calculated that the resulting convection loops reduced the thermal efficiency by 16%. I was astounded that as small a "mistake" as that sould lead to such a large reduction. (feel free to correct my numbers if I got them wrong. I'm writing this from memory) If mineral wool is as sensitive to small placement errors as fiberglass batts then I think you'd be a lot better off using dense-pack cellulose or one of the many spray foms available like corebond. Foam is tremendous at air sealing and reducing sound transmission.
Also in your proposed wall system you still have those thernal bridges every 16" or 24". In a cold climate I'd consider a Mooney wall system or if money is no object aerogel strips as a thermal break.