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Another XPS queston

Posted by jondavis08 (My Page) on
Thu, Nov 29, 12 at 8:44

I've been searching the forums and have gained a great amount of knowledge but I'm always looking to do things the "right" way.

My basement is a rather small basement with large crawl spaces on two sides. I'm assuming this is because of a high water table in our area. A B-Dry system was installed at one point connected to a sump. When losing power a year ago for a few days I found out how important the sump is. Long story short it appears that moisture was in issue is this basement.

I'm now working on finishing the basement and want to do it the right way. From what I've learned I'm thinking of insulating the concrete walls with 1 Inch XPS. Here's a link to the product that I'm thinking,http://www.lowes.com/pd_304089-210-304089.0_4294858106__?productId=3122445&Ns=p_product_price:1 first question would be is this the right product for the job? I also read somewhere that applying a water proof paint to the walls prior to adding the XPS is suggested, is that overkill? Lastly I plan on installing the framing 1 inch out from the XPS.

Again I want to do this right so I do not regret being lazy/cheap down the line. Some of the walls had been framed by the previous owner with a vapor barrier and rolled insulation, when I removed those my sinuses immediately swelled up from mold dust.

Thanks for you help so for the overkill of info!


Follow-Up Postings:

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RE: Another XPS queston

It would help to know your climate. One inch of XPS R5 (reduced to R4 after 10 years) would be adequate in the US south. North of the Mason-Dixon line, R20 is the minimum recommended by Building Science Corp.'s Dr. Joe Lstiburek. (That's actually Code where I am in southern Ontario.)

See US Department of Energy link below for Zip Code specific R value recommendations.

There's no reason to include a space between the framing and the XPS, unless you were to fill that area with fibrous or other insulation to bring the wall up to the minimum recommendation.

Sodium silicate or crystalline waterproofing are the only long-term useful sealers for walls and floors. Both are ideally applied by professionals, due to the toxicity of the prep or the material; diy's tend to ignore safety precautions.

Your link didn't work. But any of the three widely-sold North American brands of XPS boards should do. They are Greenguard/Pactiv, Styrofoam by Dow and Owen-Corning's Foamular. (There are different strength XPS boards, but the typical big box store will carry Type IV exclusively.) Tongue and groove boards work best as they help lock the ends of the boards together. Your goal is to not let the basement air touch the bare foundation.

Some of the walls had been framed by the previous owner with a vapor barrier and rolled insulation, when I removed those my sinuses immediately swelled up from mold dust.

And I bet that same method is right now being advocated at hundreds of building centres across the US and Canada. Not to mention the on-line forums that make me want to grit my teeth!

Here is a link that might be useful: Zip code Specific R Value Recommendations


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RE: Another XPS queston

Thanks for the follow up. Well I'm defiantly not in the South as I'm based in Michigan. Thanks for the link, very helpfull. Looks like I should be considering a R value of at least 11.

I'm also looking to add XPS to the walls in the crawl space, should I be considering the same R value?


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RE: Another XPS queston

Sorry just saw the that the link did provide suggestions for Crawl space walls


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RE: Another XPS queston

If I was to use a XPS with a lower R vaule than suggested would I still get the moistor control that's needed to prevent mold. I'm not too concerned about the warmth of the area but mostl concerned about any condinsation forming behind the wall.


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RE: Another XPS question

Building Science specifies a minimum(page 2) of 1" XPS for the interior basement walls. But I'd still be concerned that the aged value of R4 for XPS might be insufficient by itself to keep the above-grade portion of the wall warm enough to prevent condensation. If you're really into the penny-pinching, just insulate the first four feet below grade.

Here are the estimated savings from insulating the basement of a small bungalow to R 10 and R20 in specific locations.

Source: January 2002 DOE/GO-102002-0776


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RE: Another XPS queston

Ok getting closer to proceeding but wanted to double check a few thing. I forgot to mention that the basement is heated with it's own zone and soon the crawl spaces will be as well. Should I still be looking at the suggested R vaule(11) for the walls.

For installing is there a special adheasive to us for XPS?

Really do appericate the help!


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RE: Another XPS queston

heated with it's own zone and soon the crawl spaces will be as well.

I'm sure the space will be warm without any insulation or air-sealing at all. It will just cost a whole bunch more!

If I were planning to stay, I would try getting closer to R20. Just filling in the stud spaces with R15 high density batts will bring you to over R20.

Use foamboard adhesive for attachment, such as LePage PL 300. However, if you have an irregular poured wall--as opposed to block--buy one tube and see if you can get it to work. I never could. Mechanical attachment works best, I find--either a number of concrete screws and fender washers or running a couple pieces of strapping across the wall anchored by concrete screws. Polypropylene insulation anchors are even better from the energy savings perspective. They don't conduct the cold from the concrete wall and are easier to use and cheaper than metal attachments.

One-Piece Plastic Insulation Anchors (UCan)
Products)hammer into the drilled hole and hold the insulation without conducting cold.

This post was edited by worthy on Mon, Dec 3, 12 at 20:46


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