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Old 04-15-2012, 12:40 PM   #1
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Can I insulate my walls from the outside?


I will be residing my house, and upon inspecting what is underneath the existing siding today, I discovered the really cheap OSB that soaks up water like a sponge. So now I am planning on replacing that with the newer OSB products out there. While I am at it, and because I am sure it is garbage like everything else my house seems to be constructed of, should/can I replace the wall insulation from the outside? Are there any drawbacks or pitfalls I am not thinking of? What R value should I go with? I am located 30 miles north of philadelphia in a mixed humid zone.

Just trying to do things the right way.

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Old 04-15-2012, 10:33 PM   #2
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Can I insulate my walls from the outside?


The insulation, if installed properly, is probably fine.

Look for any mold or moisture infiltration and replaced the damaged sections. R-Value and insulation depth will depend on wall depth.

If you want to get extra R-Value into that wall, look into a rigid foam to the exterior.

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Old 04-16-2012, 11:27 AM   #3
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Can I insulate my walls from the outside?


Google REMOTE WALL if you want to install rigid foam on the outside. I would leave the OSB at the store and use plywood. OSB is not great if it gets wet. Be sure to add a rain screen when you rework all this insulation and siding. Part of your problem w/ rotten OSB may be that you have took much air leakage from the inside, carrying moisture that condenses on the OSB. You may want to consider tearing out the sheet rock and air sealing. At least do what air sealing you can, if re-sheet rocking is out.
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Old 04-16-2012, 12:22 PM   #4
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Can I insulate my walls from the outside?


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Google REMOTE WALL if you want to install rigid foam on the outside. I would leave the OSB at the store and use plywood. OSB is not great if it gets wet. Be sure to add a rain screen when you rework all this insulation and siding. Part of your problem w/ rotten OSB may be that you have took much air leakage from the inside, carrying moisture that condenses on the OSB. You may want to consider tearing out the sheet rock and air sealing. At least do what air sealing you can, if re-sheet rocking is out.

So if I read the REMOTE method correctly, its Gypsum, Insulation (Thinking Wool), Sheathing (OSB), Housewrap (Tyvek), Insulation (1 in either Extruded Polystyrene or Polyisocyanurate) and Cladding (Vinyl Siding). It does not make mention of any "air gaps" between the outside insulation and sheathing covered by housewrap. Is that by design?

I have also read that by excluding a vapor barrier on the inside of the dwelling it allows any mositure trapped inside the walls to travel inward and dry that way.
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Old 04-16-2012, 02:28 PM   #5
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Can I insulate my walls from the outside?


your area may require more rigid foam. greenbuildingadvisor.com has a blog w/ guidelines for how much. buildingscience.com may, too. if you have too little, the sheathing will be cold, condense, and get ugly. yes, no vap barrier, as the foam will really reduce trying to the outside. all but the coldest areas (zone 7 and 8) are really getting away from vb's anyway, esp if you run air conditioning. even in zone 8, they are not needed and some builders WILL NOT install one. i won't have one on the new house, unless i use membrain. i would always use a rain screen, regardless. air seal.
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Old 04-16-2012, 05:33 PM   #6
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Can I insulate my walls from the outside?


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your area may require more rigid foam. greenbuildingadvisor.com has a blog w/ guidelines for how much. buildingscience.com may, too. if you have too little, the sheathing will be cold, condense, and get ugly. yes, no vap barrier, as the foam will really reduce trying to the outside. all but the coldest areas (zone 7 and 8) are really getting away from vb's anyway, esp if you run air conditioning. even in zone 8, they are not needed and some builders WILL NOT install one. i won't have one on the new house, unless i use membrain. i would always use a rain screen, regardless. air seal.
I am in zone 4 which stipulates a minimum R-value or 2.5 for a 2 by 4 wall. I plan on using 1" sheathing with an R-value of 6.5

Through reading through the links you provided (thank you), I have decided to use plywood instead of OSB.

Per the greenbuildingadvisor website
"If you are building a house in one of the warmer climate zones — zone 1, 2, 3, or 4 (except for 4 Marine) — you don't have to worry about the thickness of your foam. Any foam thickness will work, because your sheathing will never get cold enough for “condensation” (moisture accumulation) to be a problem."

I am 1 county away from zone 5, which is why I decided to go with plywood over OSB.

You keep mentioning a "rain screen". Is that a combination of the insulation/tyvek properly sealed at every seam, or are you referring to an additional product layer?
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Old 04-16-2012, 05:37 PM   #7
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Can I insulate my walls from the outside?


rain screen. one option. http://www.100khouse.com/2010/05/14/...urring-master/
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Old 04-16-2012, 06:41 PM   #8
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Can I insulate my walls from the outside?


So the purpose of the rain screen is to create a "gap" between the sheathing and cladding to promote drying of any penetrated water. I do not do this for a living so I must ask, are you referring to placement between the vinyl siding and the insulated sheathing or between the plywood covered with a WRB and the insulated sheathing? My guess is the first option based on my research of insulated sheathing and its impermeable property if sealed properly.

If number 1 is correct, I found this on the buildingscience website. "How much of an air-gap? We know from experience that 3/8 of an inch is a pretty safe dimension4 with stucco, manufactured stone veneers, wood claddings or other claddings like fiber-cement that lie flat against the housewrap and OSB (Photograph 3 and Photograph 4). Typical vinyl and aluminum siding have plenty of air-gaps behind them without having to do anything."
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Old 04-17-2012, 11:32 AM   #9
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Can I insulate my walls from the outside?


between the vinyl siding and the insulated sheathing. if you gapped the foam, that would kill its insulating ability.
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Old 04-17-2012, 12:00 PM   #10
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Can I insulate my walls from the outside?


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between the vinyl siding and the insulated sheathing. if you gapped the foam, that would kill its insulating ability.

Great, so that being the case, do you have any opinion on the quote i posted below from the buildingscience website?
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Old 04-17-2012, 12:15 PM   #11
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Can I insulate my walls from the outside?


i generally do not argue w/ BS.com! being no expert, i rely on my judgement of what the experts do. some folks use that meshy stuff, some 3/8" ply, and some the easy, cheap way of 1x firring strips. i'll use the 1x's. here is another link you may find of interest. http://www.youtube.com/watch?v=8laxB...ature=youtu.be
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Old 04-17-2012, 06:03 PM   #12
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Can I insulate my walls from the outside?


OK, final question. What type of insulated sheathing, Extruded Polystyrene?
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Old 04-17-2012, 08:56 PM   #13
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Can I insulate my walls from the outside?


do you drive a ford or a chevy? look at the $/R-value, for one. xps is the worst for the environment, as it is petrol based (it or the blowing agents; i forget) and apparently breathes the worst, which may or may not make a stink. all are good if kept dry.

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