Identifying Old Foil-Faced Underlayment
marleyandbowie
| Posted in General Questions on
What is this old wood floor underlayment?
While inspecting an old wooden floor system we found this foil faced paper in between the plywood subfloor and painted pine floor. The plywood sits on rough cut joists over a slab in a garage, most likely installed in the 80s – 90s but could have been as early as 1955. It’s foil faced on both sides with some kind of black paper in the middle. Just curious if anyone is familiar with this product and why they would have used it like this? Seems odd to use a radiant barrier in this assembly.
Thanks!
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Replies
That is sound dampening sheet, basically a foil and butyl rubber sandwich, commonly used in car audio applications. 80s to 90s is a good guess.
*Butyl rubber is the most common material, but if your stuff looks more like black paper, it's probably asphalt impregnated cardboard.
I got curious, and Googled "foil flooring underlayment"; there seems to be a lot of different foil-based underlayment and vapor barrier products out there.
Odd to have (what appears to be) a radiant barrier product in contact with other materials, because then you just get a thermal conductor instead of a radiant barrier, but....
Radiant barriers are reflectors that deal with IR radiation, so it doesn't matter if they contact something that is thermally conductive. You could, for example, use a shiny sheet of aluminum as a radiant barrier, and aluminum itself is a VERY good conductor of heat!
All that said though, a radiant barrier sandwiched into a floor assembly between the subfloor and the finished flooring won't accomplish anything at all. The foil facing used here is serving some other purpose, probably as a slip layer.
Bill
Yes, a radiant barrier sandwiched between two materials is just a thermally conductive sheet, that was my only point. I worded...poorly.