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My
wife's office
desk is
in the corner of our daylight basement surrounded by large windows.
She has always complained that she is cold in that corner despite the
very effective wood stove that we use to heat the entire basement that
is her studio workspace. This year I decided to do something to
make her more comfortable. The first step was to improve the
insulation factor of the windows,
click here
to learn more about the window insulation panels that I designed.
 My next step was to improve the insulation of the
exposed concrete foundation
wall. I have been doing a
similar project around
the frost wall of my workshop. The inside of the basement concrete wall is
framed with 2X4s and filled with fiberglass which has an R value of
about 13. Not much when the outside ambient temperature remains
below freezing for several months a year here in Maine.
The exposed un-insulated wall is shown at left. |
  So
I decided to add 4 inches of rigid foam insulation to the exterior of
the wall for an insulation rating of about R24. First I dug down
about 8 to 12 inches and 5-6 inches away from the wall. Then
I attached 2 inch rigid foam board to the wall with Liquid Nails construction
adhesive. I used boards to hold the foam in place while the glue
set.
I had pre-cut the top edge of the foam to 15 degrees on my table saw for
a drip slope for the wood strip that will cover the top edge. I
also taped all the seams with aluminum tape to form a complete seal.
The second layer of foam was adhered with special foam adhesive because
Liquid Nails will not glue 2 non-porous surfaces together. |
 Finally
after taping all the seams I glued on a layer of T111 concrete sheathing
using Liquid Nails again. Once again I used boards to hold the
panels while the glue dried since it tended to slide down. The foam and boards all drop below
grade as far as I could practically dig which was 8 to 12 inches.
Here in Maine the frost level goes down about 36 inches. If I were
building new construction I would have wrapped the entire foundation in
foam insulation.
Note: I ran out of 2" blue foam, and had to run out and get more from a
different store where they only carry Owens Corning foam board which is
pink. It's basically the same material and R-value. |
  To
protect the exposed edges I used 1X6" lumber that I ripped to 15 degrees
along the back edge of the top board. I used pre-primed lumber and
painted all sides with one coat of finish paint before attaching it to
the wall. I beaded the edge of the wood with dark colored latex
caulk before screwing the board to the wall. I used a pocket hole
jig to drive the screws in at a very shallow angle so that they would go
right into the wood along the top of the concrete. The pocket
holes were then filled with caulk.
Finally I caulked all the seams with dark colored caulk and painted 2
more coats of good quality latex exterior paint. The finished
project blends in almost seamlessly. I am hoping that my wife's
legs will stay warmer now that the concrete wall will remain warmer this
winter!
Next year I plan to dig out from the wall and bury 2" foam 2 feet out
from the wall. The ground temperature remains at 45F year round
below the frost level which can be as low as 36" here in Maine. Trapping
that heat below insulation will help to keep the frost wall warmer below
grade. A building expert explained to me that the horizontal foam adds
an equivalent depth to the wall insulation. So by putting 1 foot against
the wall, and 2 feet out from the wall I could achieve the equivalent of
insulating 3 feet deep down the wall. I already did this on my
workshop, and hope to
document the improved insulation value later in the winter. |
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