# Basement Insulation and humidity control



## Bob Mariani (Dec 1, 2008)

Dryloc will help (maybe) Thoroseal is better. When you insulate a basement wall, the moisture now entering is trapped, so how are you planning to expel this from behind the wall?


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## Ron6519 (Mar 28, 2007)

Dehumidifiers will be part of your basement whatever you do. I would incorporate them into the design and have them emptied into the nearest sink by way of a condensate pump.
Ron


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## mcwolfe6 (Jan 26, 2010)

Bob,
That's part of the question. So is it a good idea to use the dryloc or not? Is this creating an evironment where either the wall will not be able to dry when it is saturated with moisture from the exterior or an environment that can cause any sort of issues? I'm just trying to find out if using dryloc as well as the other things I've listed is a good idea or not. If adding dryloc is going to do nothing but cause additional issues then I obviously wont use it but that's why I'm asking. For input from those with experience. So the question is "How do I expel the moisture/reduce the humidity in the basement?" Will dryloc help or is it going to cause some other problems? Is just performing the insulation steps I mentioned earlier enough to reduce the humidity without using dryloc? Do I give up on the idea of reducing the humidity in the basement by any means other than using a dehumidifier? Any useful input is appreciated?


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## VelvetFoot (Mar 9, 2009)

I put some foam on the walls and I think it's less humid down there.
I don't know if keeping a space between the foam and the fiberglass is the current thinking however.


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## Gary in WA (Mar 11, 2009)

BSC suggests *no air space*. No drylock or sealer on inside concrete wall as it has to dry to the inside. 1--1-1/2" of XPS on concrete for a climate of 9800 heating degree days (Minnesota). http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems

Compare yours:
http://pasc.met.psu.edu/PA_Climatologist/newmeans/PA_annual_HDD.jpg

Be safe, Gary


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## Ron6519 (Mar 28, 2007)

VelvetFoot said:


> I put some foam on the walls and I think it's less humid down there.
> I don't know if keeping a space between the foam and the fiberglass is the current thinking however.


 Invest in a few humidistats so you know what the humidy actually is.
It's odd that your humidity is so high this time of year. With the heat on in the house, my humidity has dropped to 30% from the mid 60% range in the Summer.
Ron


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## Bob Mariani (Dec 1, 2008)

Dryloc will not help and should not be the solution. The problem is you should not be having that much humidity. The moisture is not being properly controlled from the outside of the wall. This is where it needs to be addressed.


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## mcwolfe6 (Jan 26, 2010)

Okay, so the concensus is no Dryloc. I will remove it from the plan.

GBR, 
I'm in the 5001-6000 heating degree days area of my state. Does the building science recommendation of no air space apply to cinderblock walls?

Ron,
The humidity is currently in the 30-40 range. It's the summer time when it reaches around 70.


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## Bob Mariani (Dec 1, 2008)

no air space against the wall. Air space between foam and wall is advisable. your humidity is low not high. normal is 40-55. High is over 70


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## Gary in WA (Mar 11, 2009)

"GBR, 
I'm in the 5001-6000 heating degree days area of my state. Does the building science recommendation of no air space apply to cinderblock walls?" Yes, no air space at foam/stud wall in all their pictures, except on the spray foam. This site below shows block and solid concrete walls, and humidity problems/solutions.

The best foams to use have a perm rating of greater than 1 perm for the thickness used. This means limiting extruded polystyrene insulation to less than 1-inch thickness for walls (more than 1 inch thick and they do not breathe sufficiently) and making sure that the rigid insulation is not faced with polypropylene skins or foil facings. Additionally, since foams need to be protected from fire, and this is often done with gypsum board only latex paint should be used on interior gypsum finishes (since it breathes). From: http://www.buildingscience.com/docu...rol-for-new-residential-buildings?full_view=1

From the site I gave previously: ------ However, walls with 0.75 inches of extruded polystyrene and 3.5 inches of fiberglass batt insulation in the cavity would perform well as long as interior humidity was controlled below 50 percent during the summer. Building Science Corp.

If you leave an air space, you still need fire-stopping every 10’ both horizontally and vertically, as per safety code. This means closing off the wall from the concrete or wood stub wall at the tops, so a fire can’t go into the joist bay to spread from wall to floor, required against the foam and bottom plate.

If you have any air leaks anywhere in that 10 x 8’high of wall, it could create a convective loop, which would hamper your batts purpose. http://oikos.com/library/insulating_framed_walls/index.html Wouldn’t it also spread the vapor coming through the concrete wall to the other studs and batts instead of going directly to the inside by the shortest route? Does anyone have any thoughts or sites on this? 

Be safe, Gary


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## Shamus (Apr 27, 2008)

Bob Mariani said:


> Dryloc will not help and should not be the solution. The problem is you should not be having that much humidity. The moisture is not being properly controlled from the outside of the wall. This is where it needs to be addressed.


Agreed.

Start by routing the water away from the foundation. Anyone that tells you it can be "controlled" from the inside won't be living with the results.


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