Insulation under a wooden floor

[TractorJeff]

I've posted before that I live in a converted barn. Primary living quarters are on the second floor. First floor is room is always cold! Its my guess that they put nothing down between the dirt and the floor joists. Wife wants to pull up the carpet to lay flooring. I said if that is the case then pull up the subfloor and insulate underneath.
She said how? I said I don't know?
Background:
There is maybe 12 inches(?) from the ground to the floor joists. Also there is foundation walls approximately 18" high all the way around supporting the structure.

 

[Slowgsr]

Can you get underneath from the bottom?

 

[Bondo]

Can you get underneath from the bottom?

Ayuh,.... That would be the way to go,.....

I would have Alota work space at 18",..... 12" is pretty tight,....

 

[NUTTSGT]

If I was going to go through all that trouble, I think I would have somebody come and spray foam the foundation walls. While you are talking to them, inquire about what they can do for insulating the floor.

 

[Holzarbeiter]

If you are willing to pull up the subfloor you can nail 2x2 on the side of the floor joist 2" down and use 2" foil backed foam insulation.
Or, nail 2x2 flush with bottom of floor joist, rip treated ply to nail on 2x2s to fill in between floor joists and spray close cell foam to fill to top of floor joist.
Depending on ceiling height and what layout your ground floor is, nail sleepers to subfloor and fill with insulation, this option will mess with door heights kitchen and bath cabinetry as well as stairs.
Electric radiant floor heating could be an option as well

 

[RM209]

If you pull up the subfloor, you can install fiberglass batts between the floor joists. If so, I recommend that you use fiberglass bats with a kraft-faced vapor barrier facing the subflooring. It's probably a good idea to use "tiger teeth" (steel wire supports) so the batts don't separate from the vapor barrier. I'd also recommend that you install poly vapor barrier on the soil; it will control the moisture, which probably aggravates the feeling of cold in the winter.

RM209

 

[Voi]

Here is an article on the subject.

http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/insulating-exposed-floor

They discuss using rigid foam to reduce thermal bridging but you might have trouble getting rigid foam on the underside of your barely raised joists, especially if you need to add some sort of sheathing there to both hold in the insulation and protect it from pests.

You can also put rigid above the joists and screw down subfloor over it. But then you have to give up the room height. How much depends on how much rigid you need for your climate zone.

I haven't read that article in a while but there were some comments on bottom of page. Sometimes the comments under the articles on that site can go on for a couple of pages or more and they're often worth reading.

First thing I'd want to know is if there is something between or under the joists to hold fiberglass in place and will whatever that is provide protection from pests (and is protection from pests even necessary?)?

I would also want to know if it would be possible to tear out the current floor and joists and put in a slab with rigid underneath. Might be cheaper than insulating joists and putting down new flooring if you like the stained/polished concrete look.

Spray foam is an option but it's expensive and won't have the same effect on thermal bridging as a layer of foam under or over the joists.

 

[TractorJeff]

Pests will get blocked out if I do indeed tear up the floor. I'm thinking if I put a vapor barrier down below as I am sure it is dirt that I would run PVC Drain piping to create a RADON Vent system as this would control moisture also? My other thought is that I would only insulate and say "screw it" as it was built in 1975 and has been this way since. Meaning I would only put insulation in between the joists, then spray the concrete knee wall/foundation and call it good. In 20 years we may move and the next owner will probably bulldoze the place to build a "new" house after all "Location" is the key.
I'll read up what is on the website link provided to see what other options are!