Hello, I live in Winnipeg MB, Canada (Zone 7, North of North Dakota). I am insulating my garage ceiling to R22+ (standard pink fibreglass between 2x8 ceiling joists). I am…
LowR XPS sheathing error on garage Martin, I am in the process of converting a single detached garage into a workshop/storage venue, Winnipeg MB Canada, so Zone 7 I think (2 hrs north of Grand Forks ND). On one long wall adjacent to my neighbour's garage (2.5 foot separation between structures), I put building paper (i had 30 lb asphalt felt) over 5/8 ply, 1/2 in XPS (R3-5) to minimize thermal bridging, furring strips, then metal siding. The wall is 2x4 but with 2x horizontal bracing i had intended to put 1.5 in xps against the studs equal to the bracing but will just stick to bats now so it will be closer to 2x6 insulation (roxul or fibreglass pink -to be confirmed yet) covered by firestop drywall (fire code in wall next to neighbours garage as it is within 4 feet) then painted osb (to make shelf construction easier and so the drywall doesn't get too banged up). Thankfully I read your articles and blogs, and reread some of the building science.com stuff before doing the other 3 walls. Before I deconstruct the exterior to either add rigid XPS to an R15 or remove the too-thin layer I have (most likely option) would it be an acceptable risk to just leave this wall as is even with the non -desireble thin foam sheathing given that the structure will be only be heated to sweater temp no more than 16 hrs a week max during nov-feb as a workshop (ie I'm not living in it). For the other walls, is it acceptable to just skip the external xps insulation and go with a more traditional, batt insulation in the 2x4 cavity, 1.5 in XPS, then poly (not sure if this is required other than the code says it is here)' then osb? I know I am over- thinking this garage/man cave thing a bit much, but the idea that the cold sheathing will frost up if (when) heat/vapour moves through the wall and contact it makes absolute sense and I really wish I had figured this out before now. Thanks Mike
Posted: 07:08 pm on May 20th 2013
Thanks Martin, Thanks. Your website is extremely helpful, informative, and practical. It contains a wealth of knowledge and people like me can learn a little from your experience and expertise. Firstly, just to be clear about the wall in the first Q with the inadequate r3 XPS - should I skip the 1.5 inch XPS and poly on the interior beneath the gypsum to allow in to dry inwards? And second, I confirm that it is definitely not to be living space.
Posted: 06:42 pm on May 21st 2013