# Framing a Wall Over XPS Foam



## ConnorT (Jan 24, 2012)

So, I am going to close on a home with a poured concrete foundation in the next month or so. The first big project will be insulating and finishing the interior.

Question: After I use construction adhesive to install 2" XPS foam on all the floors and walls, can I frame up my new walls through the XPS foam?

My idea is, I've seen this on Holmes on Homes once but I have yet to see another example like I am thinking, that I drill through a 2x4, through XPS, into the concrete and then pound in a concrete fastener (that is long enough of course) to anchor my base stud. Then I frame up my wall, place the entire frame on the anchored stud and then framing nail the frame to the anchored stud and to the floor joists. The rest of the floor would be superply, or equivalent, that is glued to the XPS and mechanically attached to the concrete, followed by carpet. Is this acceptable?

I imagine one alternative would be to XPS everything, superply the floors, then mount my frames through both of those layers. 
Another would be to XPS the walls, frame straight to concrete (with vapor barrier if untreated lumber) and then XPS the floor and finish with superply.

Opinions or suggestions? Should I ask in another forum? I never see anyone XPS their floors who provides details on how they mounted their walls!

Thanks!


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## joecaption (Nov 30, 2011)

Guessing you have spent 0 time looking around this site before asking this question. It's been covered at least 100 differant times in the last 2 months.
Take a min. and look around.


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## ConnorT (Jan 24, 2012)

I do appreciate the quick response, but if the answer is a thread that you know the name of so I can search, that would also be appreciated. I searched XPS and basement keywords, etc. and you'd be surprised how many people use those words and don't do anything relevant to my question. Do you know what forum this has been discussed in recently?

I've been lurking for a few days (it takes more than 0 min to go through the entire Project Showcase forum) and haven't seen anything, so I guess I'll just have to dig deeper. Like Leonardo in Inception, or something.

Well, thanks.


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## Gary in WA (Mar 11, 2009)

Welcome to the forums! Yes, you could install the foam board first, 2" has a compressive strength of 25#per sq. in., just be sure to air seal all joints, fig. 15: http://www.buildingscience.com/documents/reports/rr-0202-basement-insulation-systems

Long as it isn't faced foam-unless you have an interior drainage system, fig.2: http://www.buildingscience.com/documents/insights/bsi-003-concrete-floor-problems?full_view=1

Be sure to air seal the f.b. on the wall--- no air to the concrete at all: http://joneakes.com/jons-fixit-database/743

Gary


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## ConnorT (Jan 24, 2012)

Thanks, Gary. That really helps out. Great resource too. 

However, the previous owner said there isn't a sump pump as the house is 83 years old, but the basement is only about 4-5 feet BG so there isn't an issue with any leaking apparently. Due to the age, I don't believe I would have a capillary break/Enka drain/perforated drain like Fig. 15 in your first link shows. Will this be an issue?

Also, what constitutes as epoxy for putting the foam against the ground? Is foam-safe construction adhesive okay, or do I need to step it up for the floors?
And should I build the subfloor on furrings as shown in your 2nd link, or can I fix it straight to the foam as shown in your 1st?

Thanks.


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## Gary in WA (Mar 11, 2009)

Foam board is fine, I was showing you other options....
Are you showing signs of moisture on the floors; water pooling, efflorescence? Have you done a moisture test with taped plastic- perhaps after the sale....

Depends on the finish flooring choice on the different systems.

Gary


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## ConnorT (Jan 24, 2012)

I will definitely be doing a condensation test. The current basement has been finished for 50 years (just walls/ceiling) without any signs of water damage to the walls or the unfinished floor, but I know that it can be deceiving. I will be doing more investigating.

Interestingly enough in my searches, I found this:

http://www.louisvilleco.gov/Portals/0/Building Safety/basement.pdf

and it confuses me. What is the "1 1/2 inch Void Space" at the bottom of the wall? Do I leave a physical opening around the basement? I just don't get it, it says that dimension is a "minimum" too.
And why would you predrill the bottom plate if you're going to put nails through it? Does that mean the nails go into the concrete? And yes, I do live in Louisville so I assume it actually does apply.


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## AGWhitehouse (Jul 1, 2011)

ConnorT said:


> What is the "1 1/2 inch Void Space" at the bottom of the wall? Do I leave a physical opening around the basement? I just don't get it, it says that dimension is a "minimum" too.
> And why would you predrill the bottom plate if you're going to put nails through it? Does that mean the nails go into the concrete?


I think the intention of this is to minimize any wicking that could occur from minimal water intrusion. Say there is a minor flood (2" of water), that break in the plates and wall finish will keep the wall system safe and will allow it to dry out after the water has been remediated. You don't have to leave that open, it would be covered by some kind of base trim (pvc preferably).

Why the pre-drilling for nails? Don't quite know, sounds odd. May be worth a phone call or face-to-face to see what and why...


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## Gary in WA (Mar 11, 2009)

The soil under the slab is *"expansive"*, and rises and lowers the slab. The 40d nails slide in the bottom plate hole not to bind so the slab can still move with one plate attached. The gap is how much movement is possible for your location (with safety factor added), Google it. Trim does cover it, nailed only to moving bottom plate. 

Gary


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## AGWhitehouse (Jul 1, 2011)

This was a bunch of gibberish we're all glad I deleted...


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## Gary in WA (Mar 11, 2009)

Louisville: http://www.stauferteam.com/content/article.html/2452941

Even others know: http://www.doityourself.com/forum/b...es/239113-framing-floating-wall-basement.html

#5: http://goulartandassociates.com/docs/Expansive%20Soil%20Damages-Know%20your%20rights.pdf

Not just in Louisville, CO: http://geology.com/articles/expansive-soil.shtml


Gary


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## AGWhitehouse (Jul 1, 2011)

Alrighty then...I stand corrected. Thanks!

Still confused though how that little system really "helps" considering the foundations crack and crumble, just seems a mere bandaid and a PIA. So I'll just assume it's along the same lines as Californians continuing to build wood houses in fire zones. Maybe someday we'll build to suit the land and not utilize a one size fits all approach...


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## Gary in WA (Mar 11, 2009)

No problem! I've been told by a reliable source (my wife) that I have trouble remembering things, though I don't remember why she said that......
I agree, I've been to CA, and seen what they build on, you/I will never run out of real estate where we live.....

Gary


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## ConnorT (Jan 24, 2012)

This is truly embarrassing, I live in Louisville, KY. Other than in the hyperlink, the fact that it was Colorado isn't mentioned in that PDF! I feel so stupid. I guess I thought it meant Louisville _co*unty*_ but I should know better that it is Jefferson county down here.

I appreciate the insight into framing techniques, guys, but I think I made a slight miscalculation of location by a few thousand miles.

Well. I guess I will be framing my basement the "normal" way then, and hitting my zone 4 requirements.


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