Foam Insulation on outside of walls?
Moved to Kenai Peninsula of Alaska (S. of Anchorage)from Ketchikan (rain country – ave. 162 inches per year and no temps below zero), so lack of daylight and cold (-20 or -30) are big factors in winter. The May issue of Fine Homebuilding (#194) article “Remodeling for Energy Efficiency” has authors placing foam insulation outside the original sheathing, then resheathing over that. Aren’t they trapping moisture inside the walls? If not, why not, and where can i read about the proper techniques to replicate that on houses up here?
Dealing with a 1950’s house currently, would prefer not to take the inside paneling/sheetrock/etc off the walls. Don’t even know yet if there is a plastic vapor barrier. Do i bite the bullet and take a wall apart?
The original sheathing is wood, some early version of t-111. For FireWise purposes here in spruce-bark-beetle-kill land, I’d use Hardi-plank.
If there is already a discussion of this, please point me at it.
looseleif
Replies
Generally - in a heating climate such as yours, you want that foam on the inside of the wall framing. I don't recall that article to know if theirs was a moderate or a cooling climate where the exterior foam is correct.
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Piffin: One house had pic showing snow, one was indeterminate but trees leafed out, and the other was winter-without-snow - and you made the same assumption i did about where the insulation "should" be. Now i wish I'd been home from sea when article came out -- I'd have written to letters column questioning it. The author(s) implies it is New England in one place. So does the author know something we don't, not provide us with full information, or is this rot-waiting-to-happen?
Seems to me the for a major article about energy efficiency, it is odd that Fine Homebuilding didn't give us more info on climate and moisture control, and that no one else asked this question in Breaktime or in Letters.
looseleif
Actually, I did not make an assumption about where the foam "should" be. I've studied it for over twenty years or more, started when I was in the Colorado mountains where temps can get more than fifty below zero and I got calls for false leaks that were actually condensation problems.If that article was from coastal NE, that qualifies as moderate enough that the insulation board can be placed on the exterior when the heating degree days are less than 6000.You can find a lot of reading on the subject at Building Science.http://www.buildingscience.com/index_html
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Thanks, Piffin, but could you check that buildingscience link? It sounds like something worthwhile but I can't get it to come up with two different browsers and multiple tries, not even by googling. looseleif
Hmmm...works fine for me
try thishttp://www.buildingscience.com/
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Piffin: many thanks, i got it to come up this time. Since I'm in Alaska, usually late at night, there IS a certain tendency for website in east to be down for maintenance, etc. Thanks again. looseleif
try http://www.buildingscience.com/bsc/
The article looseleif is talking about is by Joe Lstiburek's wife, and at least one of them is or was their own home near Boston. Learned about it at the seminar he led that I forgot to invite you to ;-)
LOL
"The article looseleif is talking about is by Joe Lstiburek's wife, and at least one of them... "How many wives does he have?;)
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Pretty poorly written, huh?
I gotta get away from this screen that's been staring at me all day....
Article, house, wife, housewife, what's the difference?
Yeah sure, "article...housewife"what the heck - it's all a bunch of words.
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zackly
Would like to add more questions about foam board and siding.
How do you install cement board or wood siding over 2 or 4 inches of foam ( blue or pink,polyiso) I know I have to strap it. But with what 1x4 or should I use 5/4 strapping? So i need very long nails(6 or 7inch) or screws to install strapping. 2X6 stud 7/16 osb two layers of 2 inch polyiso foil faced strapping and then(heavy) cement board siding . Siding company spec. say you should have 1 inch or 3/4 penatration into studs. I foud many articles on how to install foam sheating & flashing and how to extend window jams but no much on strapping over foam.
Any details or article or tips
I'm building new house in Ottawa,Ontario,Canada and would like to get it right the frist time.
http://www.grkfasteners.com/en/selection_guide.htm
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Rottenron: The May '08 article only gave sketchy details. They used "furring strips" according to the drawings, but little or no details and nothing on how the strapping was installed. I could envision a freestanding wall but why? If i was building new, I'd use 2x8s and fill wall cavities with foam. It is retrofitting that is frustrating. They were NOT putting up Hardiplank, i think, but lighter wood siding of some sort. Maybe Fine Homebuilding would forward a message? I'm ready to try that myself if no one here has more insight/input.
looseleif
I used foam on the outside with blown cellose for the insulation. Based on an old FHB article. The author said the foam acts as a vapor barrier and no vapor barrer is on the inside hence the cellose. If you have a couple hours this has been discussed alot. Check the archives.