Plastic Sheeting/Insulation Vs. Spray Foam For Pier And Beam Crawlspace

[niwashikun]

Hi,

We have a two pronged issue we're trying to address.

1. Musty smell, likely coming up through floors

2. Very cold floors in winter

After endless hours researching I'm virtually paralyzed by info overload and conflicting opinions.

I've narrowed it down to two solutions, either:

1. Closed cell spray foam insulation on the underside of the floor

2. 6 mil (or thicker?) plastic sheets over the dirt and some type of insulation under the floor

I realize there are strong opinions on both sides of the sealing/ventilating issue and I don't want to start another thread arguing those sides.

Therefore I'm looking for comments from people who have actually done one of the two solutions and can give their direct experience as to what effect it had on the above two issues as well as related problems.

My concerns/questions :

Both Solutions:

Effect on musty smells

Effect on floor temperature

Effect on dampness feeling of floor

Solution #1:

Issues with leaking pipes

Issues with liquid spilled in house

Issues with access to pipes for repairs

Solution #2

Issues with mold on/under insulation

Issues with vapor/air convection through floor

Does plastic address odors

House Facts:

-1948 pier and beam bungalow in the heights, 1250 sf, unenclosed crawlspace approx 18" dirt to subfloor.

-Original portion (ca 900 sf) oak floors (with lots of crevices) on top of diagonal shiplap sub floor (parts I've seen have lots of space between boards)

-70's addition (ca 350 sf) has plywood subfloor with various amounts of linoleum and vinyl flooring on top.

-plumbing in crawlspace, most electric and all hvac in attic.

Thanks!

[samagon]

I am by no means an expert. far from it actually.

but I would think the musty smell should be your main concern. I doubt insulation would help.

I assume you've done all the normal checks for water pooling, and that sort of thing. I would suspect that the smell doesn't necessarily have to be coming from under your house. do you possibly have a cracked pipe somewhere? with as dry as it has been of late, under your house should be dry as a bone, have you checked with a flashlight to see if there is any moisture in the ground?

unfortunately, I have no idea how either of your solutions would exacerbate, or resolve the smell issue.

as for the cold floors, I consider it par for the course on an older house and have rugs in a few strategic locations, and have some house shoes I wear when it gets dreadfully cold.

[niwashikun]

Samagon,

The insulation is for the cold floor issue. The plastic sheeting is for the dampness and smell. Although the spray foam insulation would be for both.

However I just found a study done recently in LA which gave some pertinent info. One thing they mention is that for open crawlspaces the ventilation overcomes the evaporation from the soil so that the crawlspace air has the same humidity level as the outside air. Thus they suggest that the plastic sheeting is not necessary. This seems to go against conventional wisdom as I know many people who have put plastic sheeting under their bungalows.

We've been trying to track this smell for a while. Odors can be very elusive and even more so to describe. My wife is the one who is really aware of it and I only get occasional whiffs. I'm not even sure we are smelling the same thing but it's driving her nuts, which means it's driving me nuts;-)

[niwashikun]

As I mentioned in the previous post, I found a study (link is below) which deals with crawlspaces in LA thus I will amend my original solutions to be:

1. Closed cell spray foam insulation on the underside of the subfloor

2. Rigid, foil-faced polyisocyanurate foam insulation attached to the bottoms of floor joists and sealed with foil tape and penetrations filled with spray foam

If you used the plastic sheeting covering the dirt I'd be interested to hear what effect it had as well.

http://www.lsuagcenter.com/NR/rdonlyres/D33F711D-DC4B-4E4C-9ED6-A97DCE9DB026/79806/pub3187insulatingraisedfloorsHIGHRES.pdf

Thanks!

[innerlooper]

I would eliminate a couple of possible (but somewhat rare) causes of odor:

Make sure that there are no abandoned-but-still-connected plumbing drains. For example during remodel, folks will forget a washer drain in the wall, which then vents sewer gases into walls and living space.

See if all of your plumbing fixtures are properly vented. A non-vented trap downstream from another fixture can "blow out" (lose its water seal) from air being pushed ahead of the drain water. Also an unvented trap can siphon, allowing sewer gases in. Unvented washer drains (added decades after construction) are not uncommon in the Heights.

Also a fixture drain that does has a vent, can have trap problems if the vent is clogged for some reason. A kitchen sink under a window for example might have a steel vent that has 90 degree elbows which can clog after 80 years.

Animal has died in walls or under (built-in) tub. Is your tub drain area open to the crawl space?

If this was a summer problem I would check if your AC is oversized and not removing moisture properly. Can get a hygrometer pretty cheap now like from Radio Shack etc. Much over 50% RH consistently could be a problem.

[niwashikun]

Thanks Innerlooper,

Those are good suggestions.

Our plumbing seems fine. We do have a washer in the kitchen with open drainpipe, however there is no odor coming from or around the drain and the stronger odors are in the opposite corner of the house farthest from the drain.

Our tub is open to the crawlspace and we do get cats and opossums in there. When we had our house raised I did pull a skull (cat?) from under the house but it was very old. I've had plumbers under there (during the raising) and no one mentioned a dead animal or smell. Also I finally got my wife to do a smell check and she didn't smell anything at the tubs location.

It is possible our AC is slightly oversized and we are checking into that as well. Of course it will be even more oversized after we seal the crawlspace, fix the windows and doors and deal with the insulation in the attic. There are also potential roof leaks. It's not a summer problem and I've been told by a mold inspector that the humidity levels are usually higher in the winter. Checking humidity level now won't work because we've had the windows open for weeks now.

The results of my wife's smell check were that there are two offending odors:

#1 "Dirty gym locker"

#2 "Sour"

#1 seems to be all over the place ( on surfaces and just in the air, stronger the higher you go)

#2 is more localized to the floor and window blinds.

She did not smell either odor under the house or in the attic.

We've lived here 6 years and this started about 2 years ago.

I think our next move will be to have a mold inspection.

[innerlooper]

I would still clear all your fixture drains with baking soda and vinegar, and remove traps and clean them as possible to clear all fouling.

Where does your cooling condensate drain line run? They used to allow installers to put them straight to plumbing stacks, which could allow sewer gases to enter the AC air flow. Today they are mostly run to sink traps.

Mold testing sounds good but be careful of results. The mold has to be living on something, and if RH is not high, what would that be?