View Full Version : Crawl space moisture barrier

Erwin Cox
01-27-2008, 12:52 PM
What is the code for moisture barriers in crawl spaces? Are they required and if so, anybody have a code number.

Dom D'Agostino
01-27-2008, 02:30 PM

Where are you located and what Codes are used in your area?

Paul Kondzich
01-27-2008, 02:31 PM
Is the crawl space vented, etc. etc. etc.

Peter Drougas
01-30-2008, 12:14 PM
Unless you have to back up your comments because a seller is complaining about the suggestion, I don't see why Code should be brought up.
I comment in all reports that they should have a vapor barrier on a dirt floor. It goes under the "Suggested idea" level in the report. Something they should consider doing to keep the house in good condition.
Has this become and issue with the Real Estate transaction?

Erwin Cox
01-30-2008, 05:59 PM
I'm an expert witness in a trial coming up and want to be prepared to back up the need for 6mm moisture barrier in crawl spaces. I'm trying to find a code to quote.

Jerry McCarthy
01-30-2008, 06:06 PM
If you want help here first answer the questions asked. Nobody can help without some details such as what was asked for.

Jerry Peck
01-30-2008, 08:32 PM
Where are you located and what Codes are used in your area?


What - where?

(Or, should I say 'Where - what?')

You have not answered Dom's questions and NO answers can be given without the information.

Guesses can be made, but you can do that.

Aaron Miller
01-31-2008, 05:46 AM
What is the code for moisture barriers in crawl spaces? Are they required and if so, anybody have a code number.


You really aren't forthcoming with much information, but here's my take on it. If you are being called as an expert you will want as much authority on your side as you can muster. The model building code is one good thing to have in your camp in theses circumstances. Without that reference you will be relying solely on your opinion, "customary building practices in your area", of the AHJ's (usually) uneducated guess at what's correct.

IRC N 1102.1.7 states in part "The exposed earth in all crawl space foundations shall be covered with a continuous vapor retarder having a maximum permeance rating of 1.0 perm [(57 mg)/(s · m2 · Pa)], when tested in accordance with ASTM E 96."

Go to: Plone — (http://www.buildingscience.com/search?SearchableText=crawl+space)
Look up the info based upon the area of the country you're in. Joe Lstiburek, Ph.D. and Nathan Yost, M.D. have good crawl space info on this site.

Also try IBACOS: Integrated Building and Construction Solutions (http://www.ibacos.com), Forest Products Laboratory -- Forest Service -- USDA (http://www.fpl.fs.fed.us/), U.S. DOE Energy Efficiency and Renewable Energy (EERE) Home Page (http://www.eere.energy.gov/), ad infinitum.

Don't go to court half-cocked.


Rick Hurst
01-31-2008, 07:14 AM

How many crawlspaces have you seen that have a vapor barrier in our area?

I've maybe seen 10 in the last 20 years.

Just not common in this area are they?


Aaron Miller
01-31-2008, 07:34 AM

No, they aren't common here. Even when I see a vapor barrier, it's 6-mil polyethylene that's been seemingly applied with a scattergun. I always write up crawl spaces as in need of a vapor barrier and recommend the upgrade from 6-mil polyethylene to 20-mil EPDM or PVC pond liner with solvent-welded lap joints. Those are relatively permanent and can be traversed by repairmen and inspectors without damage.

The few builders here that still construct pier and beam foundations with crawl spaces are still living in the 50's technologically speaking. The last I saw was a new 6-million dollar box in Highland Park. The builder put down 6-mil polyethylene and then covered it with crushed rock (to properly perforate the plastic, I assume). In addition he added a high-end sump pump at the high end of the sloped crawl grade and humidistat-controlled fans that were installed backward (blowing into the crawl space - useless except for pressurizing the crawl and send the moisture through the wooden floors).

When I told him he had significant mold growth on the undercarriage, he scoffed. I got him an extra pair of coveralls from the van and invited him to crawl on that damned crushed stone to have a look. Served his knees just right.