What to do about uninsulated flooring - no subfloor

[kelt65]

Hey all,

I'm sure some of you have houses like this - raised with no subfloor. Spray foam is a no-no because it traps moisture and hide termites. My floors are pretty old and there are gaps due to shrinkage, etc. I imagine the wind will whip up under there in the winter.

Is it OK to go under the house and use a quality caulk to caulk up the seams between the floor planks? Going through actual insulation at this point is not do-able, but foam panels might be an option in the future. Is caulking going to cause any problems down the road? Any recs. on type of caulk?

[nhguy]

Hi I live in NH and we frequently get temperatures below zero in the winter, so we put 2" foil-faced urethane under our floors. I left a gap around the edges, so I could seal them with canned foam. I would think you could use 1" or even 1/2 in LA and be well sealed from the winter wind. Our basements is moist and so far have had no ill effects. The crawl space part I covered with a membrane and crushed stone to hold down the moisture. The flooring got the same 2" urethane and foamed edging. We don't have termites in NH, so I'm not that up on their likes and dislikes. We do have carpenter ants, which enjoy moist wood, but I've seen none in the last seven years. GL

[Texas_Ranger]

I wonder if it wouldn't be wise to put some kind of wind and vapour barrier up first, like tyvek stapled to the entire floor from below, wrapped around the joists. Just thinking aloud! The point is you don't want warm and somewhat humid room air to get down into your insulation and you don't want the wind to whistle through from below. Then you could use regular batten insulation.

[SkipW]

In my mudroom addition (mudroom, bath and laundry) we have wide pine floors with big gaps and no sub floor. The crawl space is tiny and I could barely fit under the floor joists. Laying on my back and sliding around, I used an electric stapler and stapled 6mil plastic to the bottom of the joists for the entire addition, 20x20.

There is basically now an 8" air gap between the top and bottom of the floor joists which acts as a layer of moderate air and it also stops air penetration from down below. Just this change probably warmed the room 10 degrees in the winter and keeps it much drier in all seasons.

I'm not sure I would caulk the joints for two reasons, one is looks and the other is constant maintenance with the expansion and contraction of the seasons.

[kelt65]

Never thought about stapling heavy plastic down there, that's a thought. I was thinking caulk since it would also help keep out pests, but plastic would certainly be easier. I don't think caulk would be visible from the interior, and even if it were, I'd just use any of the products designed to fill in the gaps on the market.

[Sow's Ear Mal]

Fyi---I had huge gaps in my old pine floor. It made it impossible to sweep because dirt would collect in the grooves and just get moved from gap to gap. I filled them with a small trowel and an experimental mix of Alex brand translucent acrylic caulk mixed with 1 and a half cups of fine sawdust. (collected from the router) I wiped off any over fill with a damp cloth. It worked really well, but I do have a plywood subfloor, and not just the gaps. (floor was raised by PO's at some point and has a million huge nails so we re-installed old pine boards over it)
We also have a post and beam addition with a dirt floor a foot beneath the floor boards. We were told to insulate the short walls of the perimeter and lay vapour barrier on the dirt floor directly. Haven't done that yet, but we did do a little digging and found a bunch of cool old bottles.

[MrPowerful (WavyGlass)]

Did you find a solution? I'm in New Orleans and we've got this issue at our house too.

[greatwindowsss (WavyGlass)]

Did you find a solution? I'm in New Orleans and we've got this issue at our house too.

same problem here

[heartwood]

reported.....

[kelt65]

Did you find a solution? I'm in New Orleans and we've got this issue at our house too.

I've decided to replace my flooring entirely, but it will be expensive. After walking around on it for a year and surviving this last winter, I'm convinced there's nothing else i can do that will truly address the problem. A 1/2" subfloor + 3/4" new flooring will be pretty tight and make the house much more tolerable in the winter. When it dropped below 40F this year I could not get the house even remotely comfortable. The central furnace cost over $400 to run the first month I ran it and after that it was space heaters + electric blanket all the way. Winter sucked. These old houses need to be insulated and modernized a bit before putting in central air, I can't believe people are putting in central air with no insulation, it costs a fortune.

The reason the floors gap, though, is basically because the floor was made of inexpensive plain sawn wood, which expands and contracts horizontally. If you notice the "nicer" old homes in New Orleans have original flooring that is as tight as the day it was installed - because it is quarter or rift sawn so that the wood expands and contracts vertically. It's more expensive but not THAT much more, as it is more wasteful than plain sawn wood. But the grain is finer as well, and it generally just looks better. Most hardwood flooring sold by outlets is all plain sawn. Vertical grain cuts run between $7-$10 sq. foot, rather than $5-$6.

That said I am going to have to do some cutting, since the new floor will be 1/2" higher than the old one, which is only 3/4" thick. That hurts, but it won't be all that bad. Cutting the doors hurts the most, fortunately the fireplace hearths have a lot of room to spare.
I'm not sure I'd do much about the gaps except the sort of things people are discussing here. I wouldn't do spray foam under the house, I have two friends that did that and they say it made no difference in their bills and the cost was over half that of new flooring ($10K)!