# Moisture between foam board and Roxul



## gma2rjc (Nov 21, 2008)

Last week I put foam board against the cement wall in the basement and sealed it. The walls are studded in and I put Roxul in between the studs. 

Yesterday I was showing my son-in-law how I did it and as I pulled a batt of the Roxul out, I noticed there is moisture in the Roxul where it was in contact with the foam board.

Did I do something wrong?


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## RCGA (Mar 13, 2013)

How thick is the board?


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## joecaption (Nov 30, 2011)

Still no vapor barrier on the studs and no drywall up so the moisture can still form against the unheated wall.


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## gma2rjc (Nov 21, 2008)

It's 3/4" thick. 

Thanks Joe. Will moisture get trapped between the foam board and the poly? There won't be a vapor barrier at the very top of the space between the 2x4's, so maybe moisture can get out that way (?).

I'll be removing the Roxul that's already in place and running a fan to let things dry out, then replacing it before putting up the 6 mil poly.


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## Windows on Wash (Aug 30, 2011)

If the walls aren't up, its not at all surprising.

I still would not use poly and you need more foam at the wall than just 3/4" (not sure what you used here either but the max R-Value you have is R-4 and that just isn't enough).


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## Gary in WA (Mar 11, 2009)

Which Zone?; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Michigan

Eg. Grand rapids; R-5 (1"XPS) + R-15 = at 68*F room air, safe to only 37% Relative Humidity at the above-grade/2' down areas.

Gary


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## Gary in WA (Mar 11, 2009)

Since you thanked me, is that the correct Zone? Lol.

Gary


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## gma2rjc (Nov 21, 2008)

Yes, that's the correct zone. :thumbsup: Thanks so much for your help Gary!

Barb


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## Gary in WA (Mar 11, 2009)

You're welcome. We are here to serve. ADA the drywall, it will help immensely in keeping any air from the cold concrete, esp. if you didn't apply glue in 1' square grid pattern or can foamed the perimeter of the sheets. Remember the rims; foil-faced fb/canned foam-low expanding- more for the $. http://www.buildingscience.com/documents/information-sheets/critical-seal-spray-foam-at-rim-joist

http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/

http://joneakes.com/jons-fixit-database/743

The degree of air tightness is imperative, not even 1/16" gap anywhere..... yikes!

Gary


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## Gary in WA (Mar 11, 2009)

BTW, the Grand Rapids was using the average of 3 coldest months of the year, so with the 3/4"---if XPS- you should be OK for most of the year. The above grade foam board code requirements for Zone 5--- to *prevent* cavity condensation is; http://www.buildingscience.com/docu...ulating-sheathing-vapor-retarder-requirements

If adding fibrous insulation FG/Roxul at the rims; use 2" FB with only enough Roxul to meet (wall) code- the more you add= the less ability fb has to prevent condensation because the colder it is; lowering it's dew-point temperature, Fig.3, 4- adding cavity insulation, notice the R-value changes*=* dew-point changes; http://www.buildingscience.com/docu...ld-weather-condensation-using-insulation/view

Gary


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## gma2rjc (Nov 21, 2008)

Thanks again Gary. Buildingscience.com has a ton of helpful information. 

I didn't know Jon Eakes has a website. I used to watch his show on tv, but haven't seen it in at least 6 years.


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## Gary in WA (Mar 11, 2009)

I knew he had a website but not a tv show.... lol. He is a member here.... hasn't chimed in for a while though.

Gary


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## gma2rjc (Nov 21, 2008)

I think it's called 'Ask Jon Eakes'. He has a few videos on YouTube.


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