# Above grade block wall, framing and insulating interior walls



## Windows on Wash (Aug 30, 2011)

Rigid foam will kill two birds with one stone here. 

2" of XPS in your area would be good. No need for a vapor barrier then.

In this case, basement insulation is probably the most applicable in terms of application. 

DOE on Basement insulation: 

http://www.nrel.gov/docs/fy13osti/55802.pdf

Airtight Drywall:

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

Vapor Perm rates:

http://buildingscience.com/documents/information-sheets/building-materials-property-table

Controlling Condensation:

http://buildingscience.com/document...ng-cold-weather-condensation-using-insulation


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## ponch37300 (Nov 27, 2007)

Don't want to use foam sheets. I want to do a 2x4 wall so electrical can be run and also to give something solid to attach things to.


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## SeniorSitizen (Sep 10, 2012)

Insulation on the interior will work if you monitor the block wall interior surface temperature and keep the ambient air dew point temperature below the wall temperature.


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## ponch37300 (Nov 27, 2007)

Getting ready to do this now that it's getting nice out and need to figure out what materials I need to use. Want to put up some walls on the inside of a block building that is heated. Walls will be 2x4 studs with a treated bottom plate. Then insulated with fiberglass batts and drywalled.

Planning on using faced batts so that will be my vapor barrier correct? No need for anything else right? 

Leave a gap between the framing and the block wall?

Anything else I'm missing?

Thanks.


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## Bud9051 (Nov 11, 2015)

I hate to be direct, but your approach is not the best (or even good).
You rejected the idea of the rigid insulation against the block walls and you want to leave a gap. In your climate we can live with the vapor barrier.

Your only plus is that this wall is mostly above grade, but it will be very cold. Any moisture that migrates from the footings up through the blocks to that gap will be circulated up to the coldest surfaces where it may form ice.

As for fiberglass insulation next to (or near) a block wall, I would shift to Roxul, intended for this application.

As WOW suggested, I would still go with the rigid against the blocks and then I would install the 2x4 framing directly against the rigid. Add 3.5" of Roxul and your vapor barrier. This assembly should easily dry to the outside so the VB will help to reduce moisture levels in the building.

Bud


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## ponch37300 (Nov 27, 2007)

Bud9051 said:


> I hate to be direct, but your approach is not the best (or even good).
> You rejected the idea of the rigid insulation against the block walls and you want to leave a gap. In your climate we can live with the vapor barrier.
> 
> Your only plus is that this wall is mostly above grade, but it will be very cold. Any moisture that migrates from the footings up through the blocks to that gap will be circulated up to the coldest surfaces where it may form ice.
> ...


My approach was what I thought I remember being the "right" way to finish basements years ago. I thought that you wanted air flow between the cement wall and the stick framed wall so it wouldn't get condensation and mold? Is this way no good anymore?

As for the rigid insulation against the block wall I'm not against that. If I go with rigid insulation against the wall would this be considered a vapor barrier? If so I would not want a second vapor barrier by using faced insulation or roxul and a vapor barrier correct?


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## jlhaslip (Dec 31, 2009)

Bud9051 said:


> As WOW suggested, I would still go with the rigid against the blocks and then I would install the 2x4 framing directly against the rigid. Add 3.5" of Roxul and your vapor barrier. This assembly should easily dry to the outside so the VB will help to reduce moisture levels in the building.
> 
> Bud


Using the Foam on the blockwall and a Vapour Barrier on the frame wall will trap moisture between the two causing condensation.
I agree with the Roxul, but with no vapour barrier on the Frame wall, especially without there being an air gap between the foam and the frame wall.


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## Bud9051 (Nov 11, 2015)

@ponch "My approach was what I thought I remember being the "right" way to finish basements years ago." So much of the advice available is a carry-over from long ago. If the gap is between an insulated stud wall and a cold concrete wall (usually mostly below grade) then the air circulation acts as a conveyor to move the moisture (humid air) from the lower areas up to where the blocks are colder and the moisture is deposited. The most popular solution is to install a sufficiently thick layer of rigid insulation, then batts to bring the r-value up to code, then the drywall. 

Getting to jl's question as well, do you add a vapor barrier before the drywall? In a basement application I do not recommend an inside vapor barrier as it is difficult for the wall to dry to the outside. The only path is up and out the exposed foundation. Even with 2" of rigid insulation, a vapor retarder and not a vapor barrier, a basement wall will be able to dry to the inside. With this application being all above ground, the wall cavity could dry to the outside. Adding the vapor barrier would depend upon that moisture generated on the inside which wasn't stated. If there is no significant moisture being introduced, then omitting the VB would be fine. If the humidity is going to be high, I would want to prevent that moisture from entering the wall, and if any enters from the outside it can exit the same way. The amount that passes though 2" of rigid is very small, but does not constitute a double vapor barrier.

Bud


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## ponch37300 (Nov 27, 2007)

Ok so you guys have talked me into rigid foam on the walls. Is 1" good enough? Or do I have to use 2"? 2" will be pretty expensive and I'm going to add insulation in the studs also. Then after foam on the walls I can frame up a 2x4 wall. Run electrical and then insulate. Roxul looks pretty expensive compared to fiberglass batts. As long as there isn't a moisture issue fiberglass should be fine since there is rigid on the block wall, right? If I go with fiberglass batts do I want faced or unfaced? Is the rigid insulation considered a vapor barrier? Or do I still need a vapor barrier on the hot side, as in faced batts of insulation?

Thanks for all the advice.


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## Bud9051 (Nov 11, 2015)

Using only 1" would be marginal. If there is no moisture being generated in there, like snow covered vehicles, washing cars, growing plants , then you could probably get by with r-5. In addition you might want to use r-13 fiberglass instead of r-15 Roxul. I'm assuming this building is not living space and thus under code restrictions. The thickness of the rigid is determined by the ratio of inbound insulation to the rigid r-value. They want the inside surface of the rigid insulation to remain above the dew point. For 70° air inside that building you would want the RH to be in the range of 20% and that is dry. If the RH in that building will be 25% or higher you would want to consider 1.5" or 2" rigid. Unfortunately I've not see a reference for this on basement walls or exposed concrete walls. I have one for rigid on the exterior of a wood framed wall assembly if you want to see that for reference.

For extra margin, we can add a couple of r-points for the block walls themselves so, baring a large moisture source, the 1" should work.

Bud


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## SeniorSitizen (Sep 10, 2012)

I really doubt there is a DIYer or contractor that can insulate and seal a concrete wall to the specifications the mentioned scientists do in their labs and I doubt those people have ever built a house. 

I see this as being a great opportunity for anyone that needs employment to start a mold remediation company. I predict there will be a great demand in the near future.


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## Gary in WA (Mar 11, 2009)

Depends on if the foam board is faced or not, interior vapor control is all based on the perm rating on the exterior side of the cavity insulation. You are in Zone 6; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Wisconsin It doesn't compare to your basement requirements with the elements sheltered, the constant moisture present, or the warming of the soil by foundation heat loss; which is why there are different listings/R-values posted.
*
Read Fig.4 *to see the different foam board (or not) applications for the required vapor control next to drywall, choose your application from the samples, as well as degree of Relative Humidity you want; http://buildingscience.com/sites/default/files/migrate/pdf/RR-0410_Vapor_Barriers_Wall_Design.pdf I've linked this before about 2 dozen times, since 2010 and it was 6 years old then... way back when I first started linking numerous times in an answer - someone even called me the "link master", how times have changed 180* for some, lol.

Gary
PS. add some foil-faced foamboard under the regular bottom plate to stop air/moisture/thermal problems; http://www.greenbuildingadvisor.com...ressure-treated-sill-plates-and-building-code


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