I am looking for a cross between the insulating concrete forms and the more
common plywood form. I would like to use the insulating forms on the
exterior, and plywood on the interior.
I like the idea of heavy insulation on the exterior of the foundation wall.
I also like the idea of passive solar, and using the foundation as a heat
sink - absorb the heat during the (warmer) day and release it during the
(cooler) night. If I insulate the inside of the foundation walls, I lose
the benefit of that heat storage source.
So, the way I see it, I can either use the standard plywood forms, and
insulate after the concrete has set, or ideally, I can use the insulating
forms only on the exterior, and save some labour.
from a construction point of view, you would be better off pouring a
conventional concrete wall and insulating the outside with 4x8 rigid
foam. you don't have to use plywood--look into renting concrete forms.
I had a hard time understanding the situation exactly, but I've used
foamboard as form board for concrete foundations, and can't see why
using molds is an advantage. It certainly is not cheaper. It depends
upon the height and amount of concrete poured behind the foamboard
because it is not as strong. However, both foamboard and plywood (or
molds) could be used, and later the plywood removed, without so much
concrete on it, and used for subflooring or other construction purpose.
The HomeDepot in our area sells a relatively cheap styrofoam material
with a vapor barrier on both sides. I have put in two foundations with
gravel and drain pipe already in the ground outside the foundation,
using the foamboard as the form holding back the gravel. I used wood
stakes at 1 foot intervals behind 3/4" thick foamboard to hold back the
gravel and drainpipe long enough for the concrete to arrive. When the
concrete pumper came and the filled the void, the liquid concrete mix
held back the foamboard and gravel, and the stakes were easily removed
and discarded. As a result, I have insulation/vapor barrier stuck to
the footing of the foundation, and on the outside gravel and drainpipe.
All of this was done in one step. In a raised foundation, OSB or
plywood should be used to support the 3/4" styrofoam insulation/vapor
barrier, or use 2" thick styrofoam and place the stakes on the outside.
Hope this helps.
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