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Condensation In Wall Cavity

 
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Old 07-27-2019, 11:57 PM   #1
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Condensation In Wall Cavity


Iíve been doing a lot of reading about the best way to insulate walls. In my case Minnesota, climate zone 6.

It looks like the experts are for insulating walls from the exterior to prevent condensation. But...

most builders arenít doing that. Itís still youíre typical wall. 2x6, osb sheathing, batt insulation in cavities, vapor barrier on warm side and drywall.

So what gives? If building science is making this claim about insulating on the outside to prevent condensation then why hasnít code changed and why arenít builders building this way and why havenít I seen a real world cavity condensation problem?

I should mention MN code does require exterior insulation for basement foundation walls.


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Old 07-28-2019, 12:18 AM   #2
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Re: Condensation In Wall Cavity


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Originally Posted by JRremodelers View Post

So what gives? If building science is making this claim about insulating on the outside to prevent condensation then why hasnít code changed and why arenít builders building this way and why havenít I seen a real world cavity condensation problem?

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You have never dealt with rot in a wall cavity?

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Old 07-28-2019, 12:20 AM   #3
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Re: Condensation In Wall Cavity


I have, not from condensation but from other sources.




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Old 07-28-2019, 08:50 AM   #4
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Re: Condensation In Wall Cavity


Where did you read that "insulating from exterior" thing? Just one mans opinion maybe.
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Old 07-28-2019, 08:57 AM   #5
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Re: Condensation In Wall Cavity


If you haven't seen cavity condensation problems, someone detailed the envelope well. I've seen condensation problems both in heating climates and cooling climates.

Wall insulation systems are driven by energy code. If there inky one way to achieve the desired r value, houses would only be built one way
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Old 09-23-2019, 04:31 PM   #6
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Re: Condensation In Wall Cavity


Quote:
Originally Posted by JRremodelers View Post
Iíve been doing a lot of reading about the best way to insulate walls. In my case Minnesota, climate zone 6.

It looks like the experts are for insulating walls from the exterior to prevent condensation. But...

most builders arenít doing that. Itís still youíre typical wall. 2x6, osb sheathing, batt insulation in cavities, vapor barrier on warm side and drywall.

So what gives? If building science is making this claim about insulating on the outside to prevent condensation then why hasnít code changed and why arenít builders building this way and why havenít I seen a real world cavity condensation problem?

I should mention MN code does require exterior insulation for basement foundation walls.


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Hey Minnesota!
I'm up in Duluth. I have seen a few houses go up with two methods for exterior insulation-- a local builder up here that is improving insulating standards orders Half Sips, with the polystyrene core touching the walls-- so hes got, from the warm in winter side; gypsum--> vapor barrier-->stud framing--> batt insulation ( or mesh and cellulose with double wall construction) --> half sip--> peel and stick membrane on exterior like Grace Envs--> rain screen--> siding.

Another builder I used to work for is a dealer for Siga Membrane and Rockwool pannels. He goes --> gypsum --> mesh + cellulose--> wall framing--> exterior sheathing ---> peel and stick Siga-->4" thick Rock wool pannels--> Rain screen--> siding.

I have only seen severe condensation in new walls once--that were 18" deep in passive construction and thats because the poly vapor barrier on the inside and a too tight membrane on the outside trapped all the ambient air in the walls--- got too hot during the day, cooled too much at night and condensed. The Poly barrier is fine as long as there is a really high quality exterior membrane like Siga, or ENVS. Interestingly, the polystyrene core of a Sip or half Sip really sucks moisture out-- you can see it wick on ICF's when the day warms up-- droplets form on the outside.
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Old 09-23-2019, 06:50 PM   #7
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Re: Condensation In Wall Cavity


How a wall should/can be insulated varies hugely by locale.

Most importantly, the wall has to be considered as a "system".

Here in lower southeast Michigan, we have humid winter periods.

A wall system that works in Minnesota might well fail here.

No matter where we put the insulation, if nothing is done to prevent moisture in the air from migrating thru the drywall to the wall cavity, condensation will develop, followed shortly by mold and rot.

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