Does anyone have any info/thoughts on the effectiveness of crawlspace vapor barriers over the soil in a vented crawlspace in the bay area, and how well it reduces indoor humidity?

IMO, I think there's a lot of snake oil here.

Views: 177

Reply to This

Replies to This Discussion

It's very important in humid climates.  

It may be less important in dry climates, you'd want to consult a dry climate expert like Mike MacFarland or Rick Chitwood. Where you are has a lot of microclimates, so if it's not important for dry climates keep in mind it will probably be quite variable from one project to the next.  

I imagine if there is a "wet season" where the soil gets saturated it'd be a good idea.  

Yes, I agree that it is usually less of an issue in a dry climate. One of the problems I've seen in "dry" climates is if there is any vegetation, watering is required. Even though this can become more of an issue with slab on grade, the crawlspace can also be a water source into the building's interior. Needless to say, it does rain as well. Most downspouts in dry climates terminate at the foundation, keeping that area of the building nice and wet during rain events. When the rains (or watering) occur it is cheap protection covering the soil and preventing higher levels of moisture from entering the home. 
Now you can remove the unnecessary venting, especially if ductwork is present. 
For a good paper on crawlspaces see Craig DeWitt's Nov. 2003 ASHRAE Journal "Crawlspace Myths".

It depends where you are in the Bay Area.  If on high ground with dry soil there isn't much effect.  But in my old house in Alameda where water came up out of the ground when it rained and the soil surface was permanently wet then the effect was significant (no more condensation on windows, for example). So it isn't so much a climate effect, its a soil moisture issue.

Climate is definitely a factor, especially in the many varied climates of the SF area. Ground water needs to be controlled even with a complete vapor barrier. Radon mat systems work to remove excess moisture under the vapor barrier, but will not easily remove the ponding that may appear during heavy rains. This requires a sump as well.
Even in dryer crawlspaces I'd still recommend a vapor barrier, sealing and insulating. Though cost is always a factor to consider, especially the insulation in the moderate climates of the Bay Area. Those dry crawlspaces are typically wet sometime during the year. Even with venting the poly will help reduce the moisture load of the space during those "wet" times. 

So Blake,

Looks like your answer is "always recommend" as you have no idea or control of what may happen in the future with weather or soil.  This summer my lawn NEVER turned brown, and some people indicated their dehumidifiers were not keeping up and mold was forming for the first time ever. 

Why is it so crushing to have people not follow every recommendation we make?  I used to obsess on trying to recommend only what I thought people would buy, now I make LOTS of recommendations that people delay or disregard.  If you recommend crawlspace vapor barrier and they decline, is this a big deal?  NO!  On the other hand, by recommending things you protect yourself should something happen later.  

Recommend the vapor barrier.  Should the lack of vapor barrier contribute to a problem that responsibility does NOT lie with you.  

RSS

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Kim Tanner updated an event

Beyond Residential Testing at The Energy Conservatory

May 14, 2014 to May 16, 2014
The Energy Conservatory (TEC) is hosting a Beyond Residential Testing event. In addition we are…See More
1 hour ago
Casey Gesell posted a video

Super Attic - Attic Insulation System

http://www.drenergysaver.com | 1-888-225-6260 The new Super Attic: Advanced Conversion System -- converts your attic from a vented attic into an unvented at...
1 hour ago

Casey Gesell just added their location.
(via Member Map)

3 hours ago
H.O. Electric posted a video

H.O. Services, Generator, Electrical, Plumbing, Heating, Cooling, Belmont, Lexington, Arlington, MA

H.O. Services is your residential Electric-Plumbing-Heating-Cooling Specialist. We are an electrical contracting company providing homeowners the best Electr...
4 hours ago
Jim Gunshinan's blog post was featured
4 hours ago
Profile IconMichael and michael coleman joined Home Energy Pros
4 hours ago
Luis Hernandez posted a discussion

Air Source Heat pump or mini-split efficiency

Greetings everyone!    I have a technical questions I hope I could get some feedback! I understood…See More
5 hours ago
Jim Gunshinan posted blog posts
23 hours ago
H.O. Electric posted a photo

about us-team

H.O. Services is your residential Electric-Plumbing-Heating-Cooling Specialist. We are an…
23 hours ago
H.O. Electric added a discussion to the group News & Announcements
Thumbnail

Stay Cool With Easy To Install Ductless AC System!

Stay Cool With Easy To Install Ductless AC System!   Save $300.00 Off A New AC System For A Limited…See More
23 hours ago
Richard Wells commented on Diane Chojnowski's group Facebook Pages
"Three thousand home energy efficiency audits, and nearly a thousand retrofits in four short…"
yesterday
Richard Wells joined Diane Chojnowski's group
Thumbnail

Facebook Pages

Does your company or organization have a Facebook Page?This group is for pros who have facebook…See More
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service