View Full Version : Crawlspace Sealing, Dehumidifier requirements

paul brown
09-18-2011, 06:33 PM
I'm now moving on with my 4 year-long renovation and I need your expertise and advice on suppliers or whomever else I should seek out to make the best decision. I apologize in advance but I feel I must give you the background of what's been done so far. I'm in Summerville, SC, and have 1983-vintage low-country style house, vinyl sided (at that time vinyl siding installed directly over crappy foam board). It is a 2 story, 6 dormers (3 front, 3 back) with wrap-around porch. I've had the roof torn down to the bare plywood, all nails removed, and screws fastened every 6-12 inches, all suspect wood replaced with new plywood. Ice and water shield was covered over 100 of roof and 24 g standing seam metal roof installed. New custom gutters and aluminum gutter covers were made and number downspouts doubled to improve water removal from roof. Each gutters feed into 12x12 grated boxes tied to 4" buried drain pipe leading water 100-200 feet from hose. Before that I sealed the entire second floor from rim-joists up to roof sheathing with polyiso foiled 1/2 inch foam board, including the soffit ends, foam panel joints were sealed with ASTM foil tape as well as where foam met wood/corners. After/during roof job, original vinyl siding removed, 1/2 inch osb was installed, then folding foam panel over that, then new Miama Dade County Florida 130mph double 5 mastic vinyl siding installed. All new aluminum coil stock made for soffits etc. All new vinyl soffit installed on wrap around porch as well. I removed every bit of fiberglass insulation in the attic and had open cell foam sprayed from soffit to soffit. Foamer even removed drywall to seal foamed area over garage from the living area of house. No other insulation in attic. The foaming was done over the winter and the foamer came back and tore out more drywall to get to areas that looked like hotspots from the outside. Therefore, I'm assuming I have a sealed attic. I also had the upstairs heat pump moved, additional return vent installed and new r8 flex duct installed. The downstairs is an AC/with a 96% efficiency gas furnace. The terrible job of flex ducting under the house was re-done with total hard pipe, the unit tuned for efficiency, and a new additional return vent installed. In addition, all of the poorly installed, poorly insulated floor registers were removed from the baseboard wall locations inward about a foot and all registers located under cabinets were R&R as well.
Gas/Electric bill for this July for same avg temp/same #days was $174 vs $300 last year. Same results for August and June.
I have various brands of thermometer/RH meters throughou the house since the work was done. We keep house at 74-76 degrees, same as last year. RH in living areas this summer runs between 45-50% on most humid of days. Last year was in 60% range. However, in the Sealed attic, room over garage, and dormer mini attics, under same conditions temp/RH is 78-85 degrees and 70% RH. I think it's coming from crawlspace, the last place to address according to moisture engineer's consultation a year or so ago.

Now, with all that said, I'm to address the crawlspace. It is 32-36 inches high. The house is on concrete block pillars and the crawlspace is totally open to the wrap around porch, which has vents installed about every 10 feet. I have installed lights under there and have cleaned out all the contractor garbage from 30 years accumulation. I have removed my 6mil vapor barrier which was torn to shreds and useless and have gone under and removed left over trash concrete slabs, nails, etc. I have also removed every bit of the fiberglass insulation. The termite inspector said in July my moisture content after all the above was done was at 19%, which is about the same as any other year (17-19%). What I want to do now is seal off the vents on the outer foundation totally, then seal as much as possible the crawlspace under the actual living area and install a dehumidifier. However, the state pest control agency as well as my termite bond company says I cannot totally seal. First, My porch is integral to the living area, so I have to put up a barrier between porch and living area. Even though it is a tightly constructed tongue and groove, totally covered porch, water still gets on the porch during blowing rains and will seep under the porch area sometimes, especially if I don't squeegee off the edges (the porch is almost totally flat with no pitch). Second, this barrier can only go to the top mortar joint below joists (about 4 inches). Before the engineer came to visit, I had already purchased, well over a year ago, Raven Industries Vapor Barrier VB15, a solid 15 mil non-radon vapor barrier. I haven't installed it because I had a wood moisture engineer come to my house and he said to start at the top first and work my way down. I think I'm at that point now. Since there are piers running along the perimeter of the living area, I intend to install (powder shot gun) treated 2x2 inch pressure treated boards, further treated with copper naphthenate(sp), along the piers, both at top (4inches from top) and bottom and then screw the VB15 to these board using 1/4 inch thick by about 1 1/2 inch wide aluminum strips, again, top and bottom. Each pier will be wrapped and sealed with the VB15. The Termite company came today and flooded the piers with Termidor and put a booster treatment in the crawlspace. I'm now ready to start installing the Vapor Barrier (I'm also sealing all VB15 joints (I think they have to overlap 6") with Raven's special 4 inch wide tape. Also I have to foam/caulk any holes I find in the subflooring where pipes, wires, etc enter.

Aside from your opinion of the above, I need your expert advise on a dehumidifier: Brand, installation, proper sizing, indoor humidistat for monitoring crawlspace, condensation extraction.
I hear "Santa Fe" ALL the time. Is this a good option AND what do you think of ordering over it the internet? I have an expert electrician and HVAC guy ready to help with this part. My understanding is that it should be installed in a central location. This puts it near the HVAC air handler. Could I put it near there and use the same condensate pump for both or would I need a bigger pump to handle the increased water volume.
What about anindoor humidistat for monitoring crawlspace, condensation extraction. What do you recommend?
Also, the barrier is going to be only under the living area but there will still be that 4 inch crack at the top between floor joist and that mortar seam where 2x2, goes and VB15 goes only that high. All of the info I read says get a dehumidifier based on square footage. Does this mean that my dehumidifier will need to dehumidify the porch area as well? If I include the porch area, I'm looking at about 5300 square feet. If I do not include the porch area, it is about 3400 SF.
With all I plan to do, do I need a dehumidifier for 5300sf or 3400sf. I'm afraid since the porch will still be open to the wood above it and the ground below it, that that moisture will have to be taken care of some how.
If you cannot help me make the best choices, Jundee, please put me in contact with someone who can. I've already had 3 experts come out and I definitely disagree with their assessment based on you guys and the site buildingscience.com.
Thanks for reading this long post and thanks in advance for what I expect will be OUTSTANDING advice.
Vr, and,
Have a GREAT day everyone!
Paul Brown
Summerville, SC

James Duffin
09-18-2011, 07:05 PM
Attached is the NC code for closed crawl spaces that may answer some of your questions. Be sure to check your local codes to make sure they are the same. As you can see a dehumidifier is an option but not a requirement.