I have hardwood floors flowing from one room to another, the first room being above a basement, the second room above (3 foot clearance) soil surrounded by a partial foundation exposed to outside air/humidity conditions, but apparently reasonably graded to avoid water infiltration into the soil. The joists supporting this room have insulation with the paper facing the living space (approximately 5 inches thick), but there are likely gaps still, especially where the radiator pipe enters cuts through the joists, subfloor, insulation and floorboards. Since this is the original 1920 floor, I doubt that there is proper paper between the hardwood and the subfloor.

Going from the first room to the second room, you immediately feel the floor temperature difference, as well as the overall room temperature difference. Of course some of the warmth of the first room is coming from the basement; the coldness of the second room's floor seems excessive.

Does anyone have an idea of the proper barrier to use between the insulation and the soil? Does this sound like a temperature only problem, or a temperature and humidity problem? (PS: I do not have a moisture tester). Will 6 mil of PP sheet on the soil going up the walls partially address the issue? Should I put some house wrap (e.g. Tyvek) or some sort of sheet-type insulation on the bottom of the joists to add to the insulation already between the joists?

All and any suggestions warmly welcomed.

Thanks again in advance.

Kirk

You can cover the soil with 6mil polyethylene which will help keep the moisture level under the room lower. That does nothing for the floor temp though. You don't want to cover under the joist with anything that will trap moisture. You just create a mold problem.

The only solution that doesn't require major rework would be the reflective bubble foil under the joist. It requires that you remove the current insulation out of the joist. If you leave the insulation in place and use the bubble wrap you will create a moisture/mold problem. You can add more insulation via solid 1" or 2" 4'x8' foam insulation if you have a very cold climate. I have no idea how much if any this would help your floor temp but done properly it should seal out moisture and slow convective heat loss from holes in the subfloor. I'm going to do it to my crawlspace but I'm waiting until our dryest time of year to button it up. I want the moisture level of the subfloor joist to be as low as possible before closing it up.

I'm also drilling some holes in the joist with a paddle bit to allow air movement between joist. You don't want to trap moisture in any one area. The key to keeping rot & mold at bay is air movement and moisture control.

http://www.insulation4less.com/installa ... _space.pdf