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Crawl space in NY - encapsulated vs. vented?

8 years ago

Our 1938 house was built over a full
basement (currently unfinished, but we plan on finishing it soon). About 20
years ago, the previous owners added a room (approximately 15’ by 20’) over
vented crawl space. It is accessible from the basement through what appears to
be an old basement window that used to open to the outside. The opening is
pretty small (about ___) and was previously closed with an access panel. The
crawl space has 2 vents, concrete floor (which is dry) and block walls. There
is very old fiberglass insulation between the floor joists (the insulation is
in pretty bad shape). So the room above it is freezing in the winter, you can’t
even stand on the floor without socks – it’s like standing barefoot on concrete
outside. The floor is especially cold around the perimeter of the room where
the insulation may have been fallen out or damaged. There are 2 Runtal
radiators (wall panels) in the room so the room itself gets somewhat warm but
the floor is freezing.

Another issue is the smell that comes
from the crawlspace and you can smell it everywhere – basement, 1st
floor, etc.

The crawlspace currently has PEX
lines for 2 radiators. There are also 2 central air vents with flexible ducts
but we are thinking about removing those because we want to install a ductless
mini-split. So the only lines left in crawlspace would be PEX lines.

We are in New York (Long Island) so
it gets cold in the winter and humid in the summer.

I have been reading a lot on this
issue, and the current trend is to encapsulate the basement. But does it make
any sense if we don’t have any equipment in there but only 2 PEX lines (which I
understand don’t freeze when the temperatures drop)?

Another suggestion has been to
insulate and seal the crawlspace between the floor joists (first fiberglass and
then rigid foam panels on top, sealed with tape and caulked on the edges), keep
the crawlspace vented and close it off with access panel from the rest of the
basement. I am more inclined to go with this option but how do I make sure I
don’t get moisture trapped under the floor which would lead to rot, mold, etc? Has
anyone done this and happy with the results?

Do we encapsulate or leave the
crawlspace vented?

Comments (3)

chapel212
8 years ago
Did you ever get an answer ? I have the same exact issue and would love to know, thanks
Bongo
Original Author
8 years ago
Yes, we left it vented and just sprayed closed cell foam under the floor. (After removing the old insulation). Then we closed off the crawlspace from the rest of the basement with a panel. Just sprayed last month and so far we love it, but we'll see if the floor stays warm once the cold weather is here... But for now im very happy with the results, and it was only a $1,500 investment vs. thousands to encapsulate it. If you are in Long Island, i can tell you which company we used tp do the spray foam.
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I'm in GA with much the same weather. I question how much good encapsulation does without actually heating and cooling the encapsulated space. There's no way you could recoup the cost of installing one, even if you did the labor yourself. You'd be much better off replacing the ductwork for the HVAC, any way you can ride it out and time it to coincide with replacing the HVAC unit?
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I live a few miles west of Indianapolis, same climate as you. Here is what we do. lay 6 mil plastic on the ground overlap 12" and run it up the wall 12". Insulate between the floor joist from the box sill out 2' what ever the thickness of the floor joist. (do not insulate all of the floor). Staple r-16 to the plate and let in droop 6" onto the floor. Close and seal all crawl vents. We also condition the space by installing 2 vents into the existing duct. This will prevent condensation and keep the space dry. You may think that you're wasting heat but you're heating the floors and there will be a noticeable difference. We have been doing this for 30 years and it does work very good.
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The part missing from your description is how they insulated the floor of the crawl space, and whether they installed active ventilation. I have a new addition in progress and the architect specified 2" R10 rigid foam under the crawl space floor, with EPDM waterproofing and 1/4" drainboard under the foam and up onto the walls. The walls have 1.5" rigid foam insulation, 1/4" drainboard and EPDM waterproofing over 12" thick block walls. There is no insulation in the floor joists. The city also required 1 sq ft of cross flow ventilation area in/out of the existing conditioned area, with a continuous ventilation fan that flows 1 cu ft /minute of air for every 50 sq ft of crawl space. I plan to use a Panasonic fan that is rated for continuous operation at 10 cu ft/minute. The use of the term "conditioned space" is not consistent across the industry. For example, a basement with no heat or A/C vents is usually considered to be conditioned space. If the crawl space is not vented to the exterior, then my city requires it to meet the requirements for conditioned space. Bruce
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Went back last night to empty the dehumidifier, and out of curiosity pulled back an overlap. The house was closed up in November. The seams aren't taped, but folded back and overlapped with sand on top. There was enough water between the folds to run out when I lifted it. The ground is absolutely soaked underneath the plastic, and half a dozen spiders ran out along with other bugs and grubs under the plastic. Considering the seams aren't taped, I'm afraid we are going to have the termite equivalent of a rotten log in the forest - cool, wet, undisturbed dirt. Are the seams supposed to be taped? The wall nearest where I was at has a bricked/enclosed back porch on the other side and a big concrete patio beyond it. It hasn't rained in more than a week, so I find it hard to believe that rain/ground water is leaching that far. We are on solid red clay - the big thing in this area is having to have a perc test before you get your hopes up for a home site. MY GUESS -- they put the plastic down on wet dirt before the put any of the floor down. We had a lot of rain in the fall & winter. I have no idea what standard practice is, but I imagine that if it had been closed in and allowed to dry out for a week or two before the plastic went down, this wouldn't have been an issue. The HVAC guys had to run everything after it was closed in, so it's not like it wouldn't have been possible to do. I think the ground was soaked, the put the plastic down, and now its a saturated ground beneath the vapor barrier that isn't sealed to keep it out.
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Bongo
Original Author
8 years ago
Just make sure to do closed cell (not open cell) foam to prevent moisture and rotten floor.

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