Insulation, Radiant and Vapor Barriers - Insualtion for raised floor

I removed a subfloor on an addition that was a closed in patio in the 80's due to the floor being freezing cold in the winter and some termite issues. The floor is a raised floor comprising of 2x4s on sleepers. After removing the subfloor, to my surprise, in between the joists there is 2 inch Owens Corning Energy Shield, now sold by Atlas, that has a foil face on each side. I believe the coldness is caused by air infiltration from the crawl space and the outside into the raised floor. The raised floor next to the crawl space that is vented and cold in the winter. Also, there is a 2x4 hole from the crawl space into the raised floor. Was this done for air circulation? I would like to close it because mice and termites used it to enter the crawl space. I want to re-insulate or add more insulation to the raised floor by sealing it as much as possible but I am concerned that I may make the floor a trap for moisture after it is closed up so tightly. I was planning to seal all of the crevices with spray foam, block the 2x4 hole and either add more insulation or replace the foam board with something thicker with a higher r-value. What do you think and/or suggest. Also, there is no vapor barrier on the floor which I assume was not installed due to the insulation being foil faced. Thanks for any replies.

You are loosing a lot of heat through your floor.
The best solution is to tightly fit four inch thick sheets of closed cell insulation, polystyrene or similar, between the joists.(Leave no gaps.)
That will leave the 2x4's as the weak link, conducting your heat to the outside.
To solve this fit sheets of two inch thick polystyrene under the joists/complete floor from wall to wall making sure there are no holes.(Use spray to make good any holes.)
This will enable the heat loss from the floor to be restricted to keeping the wood warm and dry.
You do not want a situation where the bottom of the joists are in the open and as such are subject to cold and therefore condensation followed by wood rot.

Where can I find 4 inch thick foam board? The big box stores don't have it? If I use 2 two inch thick boards, is there a possibility of condensation between the boards? Also, the space beneath the joist is only about half an inch. So I was thinking the following:
1. Remove current insulation and fill all crevices with spray foam around the perimeter.
2. Install 6 mil poly as a vapor barrier by running under the joists.
3. Spray foam the gap under each joist.
4. Replace or re-use the insulation and place between the joists and spray foam all gaps along the edges of the insulation.
5. Glue and screw T&G plywood subfloor to the joists and spray foam the gap between the subfloor and the drywall.


If I can find 4 inch insulation that would be great, I contacted a manufacturer of insulation and they suggested if there is no moisture problem, to install bat insulation on top of the 2 inch insulation.

What do you think? Any responses appreciated.

Jeffzy
By all means use two layers of two inch thick polystyrene, a small gap will not be a problem as air is a good insulator, indeed polystyrene is small balls of air surrounded by a very thin layer of plastic. The air is the insulation the plastic skin keeps the air in place. Once an air space exceeds 16mm then convection starts and the insulation is useless.
Moisture only becomes a problem when the air is warm and humid and it comes into contact with something that is cold. Think of a bottle of beer straight from the fridge - the moment its out of the fridge the air round it cools and the water vapour drops out as condensation, in no time you have one very wet and dripping bottle of beer.

This is the point of using polystyrene, it may become very cold on the outside,in exceptional circumstances even wet, but being the best insulation available, that cold and any condensation stay on the outside, because polystyrene is virtually water and damp proof.

I would query "3"?
If I understand correctly, running a 6mil plastic sheet under the joists? Provided all joins are taped, this is a very good "almost vapour proof barrier" and will stop the ingress of all water vapour. Having a two inch layer of polystyrene will also keep your heat in.

I consider this an excellent proposal,it will do a good job for you.