I have a very unique house. From the looks of it, I think they tore down a barn, built a foundation, framed the house with 16x16 beams and sided it with the barn. The down side of that is it’s VERY inefficient heating and cooling wise. I’ve started dealing up air leaks inside the walls with expanding foam. It’s made a big difference so far.
There is one leak I have no idea how to fix. The entire first floor is surrounded by these 16x16 beams. Butted up to them is the wood flooring.  The space between the beams and the floor is constantly cold and lets cold air in. The floor is standard touge  and groove wood flooring. It’s pretty tight up against the beams around it. I went under the house and used foam all around the foundation. The floor is pretty well insulated but I cannot stop the air leak between the beams and the flooring. It’s so tight against each other I can’t get anything in there to seal it. I tried pulling the molding off to get non expanding foam in there but the space isn’t enough to get the little straw from the foam can in there.
Does anyone know of something I could get in there to seal it up? Any other ideas?

Probably need ms paint to understand what you are describing. I had a post and beam floor house and the plan (sold before I did it) was to put insulation bats in between the joists and secure them with mesh so they stay in place. Sounds like that is not what you have.

Maybe get a vapor barrier or something breathable like tyvek to at least prevent air movement? I don't think you are supposed to use a vapor barrier under the floor as it could cause mold, but tyvek may work.

Be careful spraying foam or attaching foam from the foundation up and onto the floor beams. Termites can hide behind it.

Spend $600 or so on a thermal camera.  Take a targeted approach and fix things that need fixing vs. shotgunning repairs hoping they work.

I was surprised where my heat holes were.  Seek shot pro paid for itself pretty quick.

Look into Rockwool Insulation, they may have something you could use.

I have one, that’s how I figured this out.
I guess I could simplify this and just say I need something to fill a gap in wood that’s on average 1/16” of an inch but is the length of my house. Some spots are more like 1/32”. I was hoping to find a liquid that will get down there and harden to stop the airflow.There is molding over it so it wouldn’t need to be pretty.

Get a spray foam kit and just apply a very thin layer to create an air seal.
Thicker if you want to insulate it.

An elastomeric paint might also work.

Spray foam won’t get down that crack I’ve tried. I I don’t think that paint is made for wood use. I’m specifically looking for something to stop the cold are from coming in.

Someone recommended to me to try liquid flex seal. I’m not sure that the best for wood either but so far I can’t come up with anything better.

How about caulking the crack shut with something like OSI Quadmax? No, it doesn’t insulate per se, but it would stop the airflow and it should allow for the seasonal movement of the wood.

Great Stuff - several varieties (fire resistant, rodent/insect resistant, large crack, 'minimal swell'). For closing gaps between floor joists, brad nail 1x2 wood strips to the bottom of the joists (both sides) creating a runner which can be used to "shelf support" tightly fitted 1/2" Styrofoam insulation. As you install, lay the 'pink stuff' on the Styrofoam shelf between the Styrofoam and the flooring with the vapor barrier correctly positioned.

Spray foam from the underside coating the entire subfloor.
Elastomeric paint will adhere to properly prepared wood.

How about some photos so people can give good advice

I don’t have access to a free photo server anymore. I definitely would. I think I got enough ideas to make something work.

Without seeing what underneath your house looks like, I'm going to assume it's at least a basic pier and beam style foundation.
You should probably do something like this:

Attached File


This pic is of an insulated floor. However, if you foam (closed cell foam) just the corners (and not the field in-between joists), you should have a very good air seal.

Don't use open cell foam for the exterior of the home. It can trap humidity and cause rot. Plus it's not as good at air sealing as closed cell, but it does have good uses elsewhere in the home.