# XPS foam on irregular basement wall



## Windows on Wash (Aug 30, 2011)

How is the interface with the framing at the top? 

The question becomes, can you get a good and tight air seal around. Otherwise, we are just creating a condensation surface. 

The air space is non ideal in this case.

Where is the home located?


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## Bud9051 (Nov 11, 2015)

Your location as Windows asked is important. Extreme cold will increase the likelihood of condensation.

Now, despite you having already purchased some rigid this definitely looks like a good application for spray foam. In stall your wall an inch or more away from the foundation keeping it nice and vertical and then spray foam between and behind the studs. To keep the spray foam costs down you could do a flash and batt approach just filling the space behind the studs and all of the irregularities. Then fill the stud cavities with Roxul.

Your location will tell us how important it is to go crazy with lots of R-value down there.

A couple of concerns would remain. This is only part of the basement so heat loss through the uninsulated areas will still dominate and once insulated those walls could get very cold so unknown how that might affect the drainage system. Does it actively handle water?

Bud


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## foos (Jan 30, 2017)

Hi guys -- thanks for the quick replies!! A few answers:

- I live in central Ohio. Reasonably cold winters

- this wall runs perpendicular to the ceiling joists, and I could most likely get a reasonable seal at the top with a can of spray foam. Also, as a side note, this portion of the wall is especially dry thanks to it being protected by a front porch

- I hadn't thought about how insulating would affect exterior water handling, which now gives me pause. Despite the interior staying dry, the sump does run periodically when the ground is especially wet (which is not so uncommon). If insulation makes the exterior water freeze against the foundation, that'd be bad...

-


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## Bud9051 (Nov 11, 2015)

Central Ohio will probably not be cold enough to drive frost very deep next to the house so the drainage concerns are probably moot. 
Before codes went crazy with requiring full insulation from top of foundation to floor I used to (and still do) suggest that home owners only insulate a couple of two feet below ground level. If you insulate 2' below grade the heat escaping from the foundation below that has to conduct through a lot of soil and that effectively amounts to a lot of insulation. Plus, the ground below is constantly supplying its share of heat. Thermal contour gradients don't support the need for full foundation insulation. The difficult part comes in when you place a finished wall in front, do you leave it empty behind (not exactly good) or just use a little less insulation (acceptable IMO).

Do some research on Roxul and see if they can convince you that it might work to fill in some of those irregularities. I've only used it for above grade walls but they suggest it for below grade.

Bud


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## foos (Jan 30, 2017)

thanks again! now I'm thinking that since I'd need to spray foam the existing walls, I might as well just frame out this wall and get some quotes on spray foaming it all. I bought just a couple of the XPS panels, and I'm sure I can at least use them for the interior walls. I will research Roxul too.


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## Gary in WA (Mar 11, 2009)

-----------------------------Welcome to the forums!------------------------

How long a time period does the sump pump run, is there any sign of interior water on any wall or the floor, or is it hidden in other part of finished room? Adding FB in front would set the thermal boundary, the Drylock/sump takes care of the liquid water. Are the painted walls ever really wet, and is there access to the drain channel from back of the new foam board. This would determine if you need to install a drainage surface in front of the foamboard or SPF...

Bud, time to re-boot; https://buildingscience.com/documents/insights/bsi-045-double-rubble-toil-trouble

SPF is expensive, if on a budget, foam board works fine on the rims/walls, Fig. 15 (drain); https://buildingscience.com/sites/default/files/migrate/pdf/BA-0202_Basement_Insulation.pdf

Gary


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