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Floor Insulation For A Tiny Crawl
Space
My house, in southwest Washington state
was built in 1959. It has 2x8 non-tongue and groove sub-floors, and oak
tongue and groove plank flooring. After I removed the carpet from one
room, I found the hardwood so surface damaged that I really needed to pull
it up and surface plane it and refinish it. This process is going well.
Here comes the problem, and the question. When I pulled up the first
planks of oak, I saw sunlight reflected off the lawn right outside a
foundation vent. There was no insulation. The space under the house is
inaccessible because there isn't enough space to get under it.
Is there an insulating material that I could put *on top of* the
sub-floor? I plan on laying an extra sub-floor on top of the existing one,
and putting in a hydronic radiant floor.
Jim
It
makes me wonder what was going on during those glorious 50's. My
girlfriend's "other" house was built in 1958, and it also has
a micro-miniature crawl space... only a rat could crawl through it. It
makes everything difficult.
Most truly effective insulation materials need more thickness than you
could possibly give up. Polyisocyanurate (such as Celotex rigid
insulation board) is about the best... you can get an R-value of 3 or 4
in just 1/2" of thickness. But... I don't know if you can walk on
it, even with the weight-distributing effects of a 3/4" plank floor
above it. There are 6 inch thick foam roofing panels that can be walked
on... so somewhere there is an answer.
Some floors are laid over a thin sheet of polyethylene foam, but this
has minimal R-value.
For hydronic heating below hardwood floors, there are many companies
that offer products. Look in Fine Homebuilding (available at most
bookstores) for some companies that sell these products. The deal is
tricky because your nails have to miss the plastic tubing that is laid
in slots in the sub-floor.
Other thoughts:
Can you excavate some of that mini-crawlspace? If so, there are heating
products that fasten to the underside of the sub-floor. I have a plumber
friend who did this in his new house recently, it works great. It's just
a radiator-like device (he called it "fin-tube") that
transfers it's heat to the wood floor above. It's all copper pipe and
aluminum fins, and is installed like any other copper plumbing.
If you dared to excavate, you could insulate around the perimeter walls?
From my experience and education (including a semester course in heat
transfer) there is minimal heat loss through the floor in most
wood-framed structures. But the floor will still be cold. I have seen a
lot of houses here in frigid Northern Michigan (common winter
temperature: -20) that have non-insulated crawl spaces... and they are
just fine, but they do waste some heat. Closing the vents in winter is a
good idea to keep pipes from freezing.
Bruce W. Maki, Editor.
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