XPS vs. Closed cell spray foam

kkal474February 8, 2009

We are still in the planning stages of our basement finishing project. We are in the process of comparing insulation options. We are vacillating between XPS applied directly to the concrete walls (1"or 2"?) vs. professional application of closed cell spray foam. On the surface it appears that the spray foam might be better but it is more expensive and I don't want to overspend for something that doesn't truly offer an appreciable improvement in insulation values and thereby comfort and energy efficiency.

Is the spray foam appreciably better in insulating than XPS or is it just more expensive? We are willing to spend the money doing things the best way but don't want to throw money away either.



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As a builder/renovator, I've used both methods.

First, the minimum R factor of either alternative depends on your climate zone.

Secondly, if cost is of no consequence, I'd choose SPF every time. It's fast--half an hour and it's done--and it fills every little nook and cranny in the sill joist area. But on a small basement or a DIY job, XPS carefully installed works well too--though, for best efficiency, it should be combined with SPF at the sills.

Whichever foam you're using, you can keep costs in line by using a minimal amount on the wall so you don't get condensation. Then frame conventionally and use fiber glass (fg) between the studs.

    Bookmark   February 8, 2009 at 7:29PM
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so you don't get condensation enough that you don't get condensation

    Bookmark   February 8, 2009 at 7:32PM
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While I can't say cost is of no consequence We are willing to invest the money needed to have a warm, dry, comfortable , and energy-efficient basement. If over time our cost savings in energy usage and in comfort level give us a reasonable ROI then want to go this route. I am having a hard time figuring out the exact cost difference between the spray foam and XPS combined with batting in the framed wall cavities. We are in Southwest, OH where it gets pretty cold in the winter (some subzero days) but hot and humid in the summer. My assumption is that we would need to have an R value of at least 12-14

An additional question I had was with regards to insulating the floor. Would it then be acceptable to lay down 1"XPS on the floor, spray foamed at the connection to the wall, with a plywood/OSB subfloor ontop? Is there a better alternative.

I appreciate you taking the time to answer my questions.


    Bookmark   February 8, 2009 at 8:01PM
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This is a retrofit. SPF requires a skilled operator, a large truck and costly equipment. The advantage to XPS is that you can do it yourself. It's not difficult for anyone with average skills. But if you're paying someone to install it, it may be cheaper to go with SPF. Installing XPS is time consuming with a lot of finicky details.

The US Department of Energy--Energy Efficiency and Renewable Energy has guidelines for your area for economically efficient insulation levels. (See link below.)

I remember five years growing up in central/north Ohio--New Bremen, Belle Centre, Findlay, Toledo. Frigid winters and broiling summers!

Here is a link that might be useful: How Much Insulation Makes Sense

    Bookmark   February 9, 2009 at 12:13AM
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a plywood/OSB subfloor ontop?

That's the preferred method of Building Science Corp., though they prefer two layers of 1/2"

Here is a link that might be useful: Building Science Corp. on basements

    Bookmark   February 9, 2009 at 12:21AM
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Yup That's Ohio for ya. 2 weeks ago it was subzero and today it was 60's. Go figure!!.

We will be doing most of the work on the basement ourselves without a defined time-line. Some things we do plan on hiring out but for the most part are hoping to DIY. WE could probably do the XPS, particularly since we are not on a time line but have to consider the value of our time as well. My hubby travels for work a fair amount and that may prolong our installation period.

We are going to call a few guys out for quotes and see what they come back with and try and do a direct cost comparison and see where we fall. We talked to a guy the other day that does the soy-based closed cell foam so I suppose we will start there.

I am still confused as to whether or not to insulate the floor with XPS or put down a plastic layer product such as the DeltaFl I have heard about. My biggest concerns is to have a warm and comfortable floor. We will most likely use a combination of flooring materials including tile, engineered HW, and carpet. I have hear that a lot of people simply put down a thick pad with carpet and call it a day but I am not sure if that really is the way to go.

Thanks so much for your information. I greatly appreciate it.


    Bookmark   February 9, 2009 at 8:32PM
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