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

Rob Moreno is now a member of Home Energy Pros
9 minutes ago
Bud Poll replied to Kaushal Bharath Raju's discussion Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.
"Hi Kaushal, First step is to understand where you are in terms of energy costs.  If current…"
2 hours ago
Kaushal Bharath Raju posted a discussion

Affordability & Deep Energy Upgrade/Passive House Retrofit in Berkeley, California.

We have a small 1940s single level house (1005sqf) in Berkeley, California that is in need of a…See More
9 hours ago
Christopher Morin posted a blog post

5 Things New Energy Efficiency HVAC Contractors Need to Know

1. Do not sell on Price! Use 'Simple Payback'The price of High-efficient equipment will undoubtedly…See More
15 hours ago
David Eggleton commented on David Eggleton's group Considering Permaculture &/or Transition
"In August 2014, in Minnesota, there's another unprecedented opportunity to meet and mix with a…"
21 hours ago
Glen Gallo commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"Nate, RE: Duct test On my own home and a rental I have tested more than once over the last many…"
22 hours ago
Profile Iconangela hines and Charles Goldman joined Home Energy Pros
yesterday
Jeff Flaherty joined Diane Chojnowski's group
Thumbnail

Tools of the Trade

A hammer and a saw used to be the key tools for home contractors. Today, the best-in-breed also use…See More
yesterday
Jeff Flaherty joined allen p tanner's group
Thumbnail

Energy Auditing Equipment for Sale, Trade or to Purchase

Discuss the pros and cons of the equipment you are interested in prior to purchase. Post equipment…See More
yesterday
Debra Little joined David Eggleton's group
Thumbnail

Considering Permaculture &/or Transition

Some who work to increase energy efficiency and intelligent/wise use of energy are, and some will…See More
yesterday
Jim Gunshinan commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"Thanks for all the comments. Yes, it is interesting how the duct leakage grew over the years. Maybe…"
yesterday
Ed Minch commented on Jim Gunshinan's blog post Energy Upgrade California—Up Close and Personal
"What sort of energy bill do you have now, what is  your target bill, and what will it cost to…"
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service