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Discussion Forum

Crawl Space Encapsulation?

designer | Posted in General Discussion on July 7, 2005 09:32am

Seeking a “Professional” opinion.

I recently moved into a new home in coastal NC. Within one week of turning on the air conditioning water droplets appeared on the mil poly laid on the dirt in the crawl space. The crawl space is 5 blocks high and has the recommended vent size and count.  The siding is brick all the way down to the footing. R19 bats between the floor joists (w/o moisture barrier). All heating and air handling equipment is in the attic. No ductwork in the crawl space, no water or damp ground under the poly, no other signs of moisture entry through the walls. All other venting, i.e. bath and dryer vent to the outside. House has gutters channeling water well away from the house. Grade does pitch from the foundation. 

I had it checked out with the following results:

  • Light sweating on floor system
  • Light mold spores growing on floor system/ground (although I cannot see them)
  • Humidity/dew point: outside 54.7% crawl space 71.2%temperature: outside 77.3 degree, crawl space 72.0 degree

They recommend “Crawl Space Encapsulation” with a dehumidifier at $3.00/sq.ft.

Its been two weeks since inspection and moisture appears no worst or may be drier. To the best of available information, only one house in the entire development has a closed crawlspace. Homes here age up to 15 years old.

Am I being Taken? Any other recommended option? Leave it alone as its not abnormal?

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Replies

  1. User avater
    Soultrain | Jul 07, 2005 10:19pm | #1

    I've been reading up on this stuff (dealing with moisture, fungus, etc) as of late for my house project.

    One idea (I'll leave it to others to opine how viable an option it is) would be to mix up a solution of borax & anti-freeze (Use the propylene glycol rather than the ethylene glyco) & coat your floor joists using a garden sprayer or paint brush.  Be sure to wear breathing & eye protection.

    This should kill any mold that is on there & since there is no running water in your crawl space (at least I would hope there isn't), it will prevent it from returning.

  2. User avater
    BillHartmann | Jul 07, 2005 11:50pm | #2

    I know nothing about the cost.

    But I just posted this a few days ago to some one in Charlotte

    http://www.jlconline.com/cgi-bin/jlconli...t/View/0408fixi

    "Fixing a Wet Crawlspace A thorough cleanup, dehumidification, and an air-sealed poly ground cover can turn a slimy crawlspace into a dry, safe environment Jeff Tooley In North Carolina, where I live and work, enclosed crawlspace foundations with small vent openings are very common. Most of those crawlspaces experience high humidity, and many have problems with mold and rot. My contracting firm, The Healthy Building Company, specializes in sealed and insulated crawlspaces, which the newest version of the International Residential Code now allows. Instead of vents, a sealed crawlspace has a continuous vapor barrier to keep ground moisture out of "

    $2.95

    The author is in Bear Creek, NC so it is similar conditions to yours.

    He also had this one on conditioned CS for new constrcution.

    http://www.jlconline.com/cgi-bin/jlconli...t/View/0310buil

    And hear is a similar aritcle on sealin CS. It is $3.50. But it is in the March 2003 FHB (#153) and you are more likely to find it at a library.

    And look at this.

    http://www.advancedenergy.org/buildings/knowledge_library/crawl_spaces/

    Has links to a number of articles include the NC code that allows unvented CS

    Vented CS might have been OK when they where used in a dry area and well vent BEFORE AC WAS USED. But AC is going to make the CS much cooler

    That last link is specific about NC.

    I know an engineer in Wilmington that I think has been involved in crawlspace issues if you want a 2nd referal.

    I just checked the weatherunground.com for Wilmington and for yesterday the dewpoint ran 72-75. So unless you can keep the crawlspace warmer than 75, including all pipes, ducts and floors you will get rain in there.

  3. dIrishInMe | Jul 09, 2005 03:18pm | #3

    I'm a builder in Raleigh and have yet to see a sealed crawl space.  I have read several articles on sealed crawl spaces though and will say that the concept makes sense.  In our part of the country I think it is kind of bleeding edge technology though.  Personally I like to stay on the leading edge, but stay away from the bleeding edge :-) One thing to think about with sealed crawl spaces is are you going to be trapping radon gas within the building envelope? - Although I think the presence of radon in Eastern NC is fairly low. http://www.epa.gov/iaq/radon/zonemap/northcarolina.htm Understand though that in a sealed crawlspace configuration, air still has to be circulated with a minimum number of air changes per hour.  This is normally done via circulating conditioned air from the HVAC system which means that whatever air is down there will be circulated directly to your living area. 

    Personally I think it is bit premature to jump into a several thousand dollar retrofit for your crawl. 

    Possible stupid question... You said: "Within one week of turning on the air conditioning water droplets appeared on the mil poly laid on the dirt in the crawl space."  I'm assuming the water droplets are on the top side of the poly.... 

    Are you sure that some of this might just be due to water that got into the structure during construction and has not yet got a chance to dry out?  It sounds like your house was under construction this spring, and the house undoutidly got rained on before it was dried in (perm roof on).  A minimal amount of moisture in the crawl is normal for this part of the country.  Talk to your neighbors and if they don't know what their crawl is like, ask if they would mind if you took a quick peek.

    Question: is the poly vaporer barrier covering 100% of the crawl space floor?  When I did my personal crawl, I used a special poly (Tu-tuf), lapped and glued the seams, and ran the plastic up the wall about 6" - 12"  such that the plastic was extending to grade, and glued the plastic in place to the walls.   I have never seen a commercially built house with crawl poly installed that well, but if the moisture is really that bad down there, I would think that your builder might just be willing to send one of his guys down there to tighten things up to 100% coverage (assuming it is not already) as this would mean minimal expense for him.  I'm not talking glued and all that, just full coverage.

    Some old school guys think that less than 100% coverage is "good for the house" in that it prevents your hardwood floors and trim from drying out too much, but I say that is BS.  6 or 7 years ago I even had a building inspector make me leave exposed dirt... I won't say how I dealt with that after the final inspections though... :-)

    In your report it gave the temp and dew point in the crawl.  What would be more interesting would be the moisture content of the floor joists down there.  The danger to your house resulting from excess moisture in the crawl space in addition to mold/mildew is rotten wood in the structural members.  A moisture meter costs a few hundred bucks, but your termite co. can probably check it for free - my guess is that you had soil poisoning as part of the construction and have at least a 1 yr termite warranty in place.  Soil poisoning is required in all building jurisdictions I build in and generally they are done by pest control companies.  Pest control companies in this part of the country know all too well that the type of termites we have like moist meals.  Moisture levels of around 20% in framing members are cause for corrective measures.  

    The report also said "Light mold spores growing on floor system/ground (although I cannot see them) "  Yea, well, I bet that probably applies to every surface in the state of NC... :-)

    Also you said: "Humidity/dew point: outside 54.7% crawl space 71.2%temperature: outside 77.3 degree, crawl space 72.0 degree"  Must have been a cool day... I'm a little confused about the way the numbers are presented because normally dew point is is expressed in degrees.  Anyway, was the temp at the time of the test was below the dew point?    I wonder if you have any large air leaks of conditioned air from the house into the crawl?  Like maybe under a bath tub, or other large penetration in the subfloor. 

    At this point, personally, I'd do the "wait and see" but if you are bent on doing something immediately, you might want to look into humidistat controlled powered foundation vents.  Do a Google on "powered foundation vents".  Not saying this would be a great solution, and a little pricey, just saying that it would be far cheaper than the $3 a sq foot you have been quoted.  I think I even saw these for sale at Lowes.  Or, how about renting a good sized dehumidifier, letting it run down there for a week or 2, and then wait another few weeks to see if the moisture returns.

    BTW - good post - concise and complete info provided...

    Matt



    Edited 7/9/2005 8:30 am ET by Matt

    1. designer | Jul 09, 2005 11:29pm | #5

      Thanks, Matt, I think I'll play the wait and see game for awhile. The same report listed the moisture content of the wood floor Joists at 29%. (of course this report was compiled by the guys who only do Encapsulated systems). I know none of the builders here add the "Dry" system to new construction.

      The poly covers the entire ground and is pinned at some places. No poly up the wall and I can even see a couple of inches of dirt in a few places.

      Your Idea of renting a large dehumidifier and drying things out intrigue me and I could improve on the poly coverage myself for a lot less then the five grand.

  4. User avater
    BossHog | Jul 09, 2005 03:45pm | #4

    Here's a sample of the stuff at http://buildingscience.com/ regarding crawl spaces. There's much more, but this is a good start.

    http://www.buildingscience.com/resources/presentations/pacny/04-crawl.pdf

    http://www.buildingscience.com/resources/articles/24-27_Yost_for_author.pdf

    http://www.buildingscience.com/topten/south.htm

    The world is a dangerous place. Not because of the people who are evil; but because of the people who don't do anything about it. [Einstein]

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