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Rifraf
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# Posted: 25 Feb 2012 10:08 - Edited by: Rifraf
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I saw some folks leaving air gaps in the vertical walls next to the outer sheething so water could drop down and not touch insulation..
in the video they just put 1/4 inch strips of rigid foam against the sheething as spacers ,leaving small air channels then applied the insulation. I've never ever heard of that before.. under what conditions would that be required ? maybe very humid locations like New Orleans or Florida ?
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toyota_mdt_tech
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# Posted: 25 Feb 2012 12:33
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I would think rot would be an issue. It may have been an afterthought, ie didnt install house wrap under the siding because no plans to heat it and then changed their minds. If that was the case, maybe wrap the siding, then the siding would be the underlay, vapor barrier over the top, then install some horizontal siding over it all.
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Rifraf
Member
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# Posted: 25 Feb 2012 12:50
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interesting. my premade shed that im converting doesnt have house wrap, should I consider adding some sort of air gap before having the wet dense cellulose blown in the vertical walls ?
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MtnDon
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# Posted: 25 Feb 2012 14:24
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No air space in walls. Leaving an air space against the outer sheathing is simply providing a nice place for condensation to occur, and more than likely there will be condensation if you do that. Let the blower guy pack the entire cavity full.
Ideally there would be a layer of wrap or building felt under the exterior wall sheathing. This is one of the problems with re-purposing what was designed as a shed. There are many older homes built like that; no weather resistant barrier on the exterior. So it is not 100% bad; nor is it 100% good, to not have the wrap under the exterior sheathing.
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Rifraf
Member
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# Posted: 25 Feb 2012 16:12 - Edited by: Rifraf
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MtnDon, would it be of any use to paint/seal the interior side of the structure before the insulation is blown ?
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MtnDon
Member
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# Posted: 25 Feb 2012 16:58
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Before I answer, where are you located again? City or loose geographic area, like SE part of (whatever state) will do. I forget and need to know the climate type; hot 'n' humid, cold, whatever.
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Rifraf
Member
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# Posted: 25 Feb 2012 17:35 - Edited by: Rifraf
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South eastern Missouri about 50 miles east of Springfield (largest nearby town)
or almost on top of Mansfield Missouri if you were inclined to Google Map that city , thats pretty darn close to my cabin, within a few miles.
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MtnDon
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# Posted: 25 Feb 2012 20:57
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That's what's known as a Mixed-Humid climate. Since you will be running A/C for a good chunk of the years you do not want a vapor retarder closest to the inside space. It would be great if the outside was clad with an inch or so of foam with the exterior finish panels/siding over that. But that's not what you have.
When the A/C is running the building will dry to the interior. The warm side of the wall is outside. That's where we would like to see some vapor retarder. The A/C removes humidity and so any moisture in the walls will want to move to the inside. So no vapor barrier there. A vapor retarder inside would very likely cause condensation against the vapor barrier.
Before the wet blown cellulose is installed have a careful look from the inside, at the stud to sheathing interface. Make certain there are no gaps. Application of a small bead of caulk can help seal that joint and reduce or stop air infiltration. Then on the outside each panel joint should be caulked to prevent water getting through the joint. Using clear paintable type on the exterior is probably best. Inside the wall pure silicone is the best. (Paint or stain will NOT stick to pure silicone... read the labels)
I don't think painting the inside of the exterior walls will accomplish much, but also don't think it would hurt much either. The caulking against air movement is probably worth more. And keeping the exterior stain or paint coat well maintained to prevent as much absorption of water from the outside as possible.
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Rifraf
Member
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# Posted: 26 Feb 2012 13:39 - Edited by: Rifraf
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Thanks MtnDon.. One of the other members here has a similar cabin to mine (shed) and he put a coat of polyurethane on the outside.. do you recommend this , or just oil based stain?
This member if I recall is in Texas
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MtnDon
Member
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# Posted: 26 Feb 2012 14:56 - Edited by: MtnDon
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I don't pretend to be a paint and stain expert. Living in the desert I have learned to despise clear finishes as they don't last long in the summer sun. A few years and the surface is cracked and peeling. Then it's a hell of a job to refinish nicely. So we pretty much use nothing but the best quality paint. I'd ask at a genuine paint store, not a big box store; some big boxes may have a good paint person but most only have people who know how to run the color match computer.
maybe something of use here...
http://www.treesearch.fs.fed.us/pubs/8818
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Borrego
Member
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# Posted: 26 Feb 2012 21:35
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Living in one of the harshest climates there is, the desert, where temperatures can vary 40 degrees in a day (although it is dry) the motto is: prime, prime, prime; paint , paint, paint
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