Is there a thread on crawlspace encapsulation?
 

I am staring down the barrel of a new project that is going to slow all other projects down for a short {I hope} period of time. I need to seal up and dehumidify my dirt floor crawlspace.

The wife and I built a single family house in 2002. It's about 1500 sf heated area and a porch that wraps around 3 sides of the house, all within the exterior perimeter of the dwelling. When we built it, we did what was the norm in the area and put it over a crawl space. We covered the ground under the heated part of the house with black plastic sheeting and ignored the part under porch. :o We've been struggling with high humidity under there ever since. All we've done {that we thought was} constructive was install a squirrel-cage fan on a timer to circulate air under the house, exhausting it out a foundation vent. Relative humidity is still a problem at over 80% most of the time, complete with some mold on the floor joists.

I wanted to farm this work out so I could continue with the two other projects I'm working on, but more than $5500 to encapsulate under just the heated part of the house was considerably more than I am willing to pay. :eek: So....

I have this plan that I'm currently going forward with. I've ordered some 12 mil three ply vapor barrier plastic(?) sheeting and the corresponding roll of seam tape and I'm going to put it under the porch area, including going up the inner and outer foundation walls about two feet. I will try and fasten it to the foundation walls with a polyurethane adhesive that comes in a caulk gun type cartridge. I expect that to marginally improve the situation. When that is complete, I will order more of the vapor barrier material to do under the heated part of the house while I address the mold problem.

I'd love to hear from anyone who's tackled this issue already and may have some helpful hints.

Thanks,

Mark

I laid the typical 6mil vapour barrier on the floor of my crawlspace. There were no vents in the space, but if there were I would have blocked them off. I stapled the VB to the header as high as I could possible get it, then jambed some insulation batts against the walls. I didn't bother with any adhesive, just a very large overlap of the pieces.
Photo

Do you happen to know what the humidity was before and after you put the plastic down? Do you have an annual termite inspection where you are?

I ask the termite question because our inspector wants us to leave at least a couple inches between the top of the plastic and the wood so they can see termite tubes if they come to visit.

Uh oh, I hope you weren't doing this during the summer. The dew point of the outdoor air in the summer, in almost everywhere except the desert is higher than the crawlspace temperature. You are essentially bringing loads of moisture and exposing it to surfaces where it will condense and mold.

I assume you know this now as you are on the right track by wanting to seal up and dehumidify the space.

Hi,
You're definitely on the right track IMHO. I think crawlspaces are very misunderstood and cause many problems for the homeowner.

Crawlspaceinfo.com has some great information.

When I constructed our house I was required to "encapsulate" our crawlspace. I threw down some black 6mm visqueen and passed inspection. Now it is sagging on the walls, some spots on the floor have torn- I need to do it properly.

I have radiant floor heat in the floor over my crawlspace, so the floor has lots of fiberglass insulation, but fiberglass insulation doesn't stop airflow, odors, moisture etc., I don't have any of these issues, the floor of the crawlspace does have a vapor barrier and there are no open vents, but the floor should be sealed for energy reasons and an ounce of prevention.;)

My current project is adding rigid insulation below the fiberglass, to add R value and keep the fiberglass from hanging down. When all the rigid insulation is in I plan on using foam to seal it air tight.

Another thing I may do is install Tyvek across the bottom of the joists as an additional measure. I contacted a DOW engineer and she said that would be an excellent application for Tyvek. She explained that basically a floor is just a horizontal wall. IMO the floor cavity should be protected like a wall cavity. I wouldn't want wind and moisture flowing across the back of the sheetrock in my walls, why would I want it on my floor?

The crawlspace is closed off, but air still moves as it is heated and cools down.

I think there would be many benefits to heating the crawlspace. Heat moves to cold, if it is warm in your crawlspace heat is moving from your home though the floors insulation (albeit slowly) into your crawlspace. If your crawlspace is warmer than outdoor it is sucking heat out of your home.

I have been considering ventilating the crawlspace with a heat recovery ventilator/ heat pump. Something like this, but with 110V Genvex Heat Pump and Heat Recovery Ventilation Solutions
The fresh air would take care of any odors; the heat pump would heat the incoming fresh air in winter. In the summer the heat pump would dehumidify the incoming air and provide cool air below your floor which is better than heat in the summer. The unit wouldn't have to be very large, especially in summer. In winter, even a little heat in the crawlspace would decrease the delta T and with lots of insulation, very little heat should get sucked out of your house and into the crawlspace.

Good luck with your’ project. Keep the gap for termite inspection and check out the crawlspaceinfo.com website it has lots of great information.

Thats my plan too. Let us know how it works out!!!!!!!!!!

At my old house I talked to the pro's about my crawlspace.

It has issues with rodents, and just being an unpleasant musty area under the house. It was basically poly not joined at the seams on the dirt, and at the top, it went plywood, fiberglass insulation, floor. The mice and rats found gaps and got into the fiberglass.

Their plan was to come in, open it up as much as possible, tape the poly correctly then pump a concrete pad in place. After that had dried and most of the moisture was gone they'd pull the plywood and insulation out, close things back up but leave the required amounts of venting and then spray foam from the cement, up the walls and then across the floor until it was 100% airtight. Closing up the vents could have been done but by code I would have had to heat the space after that.

They wanted lots to do it. I figured I could do it myself for about $5k. While saving up the money I went nuts with aluminum flashing and steel wool and fixed the rodent entry issue and decided it wasn't worth fixing. I of course didn't have anywhere near the humidity issues you're having though. Being as anal about power usage as I am now, I'd probably do it if I still had the house.

One way to seal up the ring joist/joist/sill area is to spray foam the ring joist to sill plate joint from the inside, add some fiberglass insulation, and finish with rigid foam board. Cut the rigid insulation a half inch or so undersize all around and wedge it in place with small chunks of scrap foam board. Spray foam to seal. The vapour barrier can be stuck with acoustic sealant and taped to the foam board.

Greg

http://i194.photobucket.com/albums/z.../P4130243a.jpg

The vent fan in my crawl space is pulling air out from under the 6mill poly via a drain tile that is under it, this is to keep the foundation drier so it doesn't crumble, it tends to exhaust very humid air and pulls the air away from the crawl space instead of pulling more moisture in to the crawl space, that fan is then on a humidistat so as the crawl space humidity goes up the fan kicks on.
Our plastic sheeting is foamed around the outside edges with expanding foam and polyurethane calk in other places, the caulk does a much better job of gluing and sealing.

My next plan is to have a timer switch installed as well so that the fan kicks on once a day no matter what the humidity, just because the humidistat is on the non vented side of the plastic.

As I said earlier, I ordered the vapor barrier plastic material and a roll of tape {on Wed, 4/11}. Americover.com sent me an email with my UPS tracking number on Thursday, 4/12 proclaiming my order had shipped and would be delivered on Tuesday the 17th. I checked the UPS site along the way and it said my order was on schedule for Tuesday delivery. So last night I got home with great anticipation. I didn't see my vapor barrier when I got home, but my wife points me to a shoebox size package. 3 lbs. Box 1 of 1. :confused:

I call Americover and spoke to a polite lady named Tammy. It seems my tape shipped from their location and the vapor barrier material drop ships from maybe Illinois. She wasn't quite sure of that, but it shipped yesterday and is scheduled for delivery this Thursday, the 19th. It wasn't like I planned to install it last night so after a moment of reflection, it was a silly kind of funny. Let's hope it comes tomorrow. I do want to get it at least mostly installed this weekend.