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Insulating Floor above Crawlspace

skyhigh82's picture

Want to insulate the floor above a crawlspace with fiberglass kraft faced batts. Area above crawlspace has oak flooring installed with nails showing through sheathing. If I use Kraft faced insulation and stuff it next to the floor sheathing and the nails puncture the vapor barrier, will this cause any issues, or is there a better way?

Insulating a cold floor (post #207466, reply #1 of 2)

Keeping in mind that heat always moves to cold and that the floor is attached to the foundations, walls and indirectly the roof, there is a constant movement of heat by conduction from the warm air in the room to the outside via the floorboards.

A better way is to lay closed cell insulation on the existing floor, closely butted polystyrene sheets or similar and to lay a new glued t&g OSB floating floor over. This will ensure there are no drafts or heat bridges and you will save money and have warm feet.

The nails will not be a (post #207466, reply #2 of 2)

The nails will not be a problem (other than poking you in the hand as you install the insulation). 

Unfortunately, fiberglass insulation installed "open" like that loses a lot of effectiveness, but it's cheap and relatively easy to do.

There are plenty of other schemes, though most involve foam, which is going to cost more.  A simple thing you can do is install the fiberglass, then cover it below with Tyvek.  This will at least double the effectiveness of the insulation.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville