If I finish my basement and start by placing insulation foam board
against the basement walls, which way should the foil face ? I have
seen it installed so that the foil faces the interior, but logic would
lead you to think that the foil should be on the outside and the foam
Any help is appreciated.
Please don't top post.
Be careful with this advice. The actual rule is; place vapor
barrier on the "warm" side of the insulation. In the south,
that is the outside. So, it depends on where you are living.
Since this is a basement, I would assume that it is in the
north. We don't have basements down here, so if you are up
north, put the foil on the interior side. In a basement
installation, it really doesn't make a whole lot of
Inside, if there's only 1 and no airspace between the board and the wall.
That way, the foil adds about R2 to the board insulation value. The board
itself is a vapor barrier, so from that point of view it doesn't matter
where the foil goes.
Double-foil board will work better with an air gap between the foil and
the wall, but the wall foil needs another vapor barrier on the wall itself
(eg polyethylene film) to protect the foil from moisture.
You were correct on the location: Chicago suburb, New construction.
I checked with my local 'Home Depot' and 'Lows' and both carry 1/2",
3/4" and 1" single and double foil sided foam board. But, if I choose
double foil sided, I need to cover the wall with a plastic first ?
(glue it up or something ? )
Is it worth the difference in price to use 1" instead of 1/2" or
Is there a particular name brand that I should use, or stay away
from ? or just use whatever is in stock ?
when I was doing my basement, this group was very helpful. They pointed me
to the Building Sciences Corp site for information on basement insulation
All your questions will be answered in their literature. I found it to be a
Ok, I read it and if I understood it correctly. You should never
attempt to trap moisture, and foam board with-out foil or plastic
backing should be used in the basement. Right ?
It even stated that insulation between the studs without a paper face
should be used.
I would go with the extruded polystyrene (Dow Blue or Owens Corning
foamular). The foil faced insulation is polyisocyanurate which can
soak up water--a bad thing on a basement wall. If you have room, I
would go with 2".
Just to follow-up...
I used 1" pink foam board spot glued to the basement walls using PL
adhesive, then unfaced fiberglass insulation. No vapor barrier. I probably
should have used 1/2" green board sheetrock, but didn't.
If you have ever had water, I would recommend not putting the fiberglass
insulation all the way to the floor. Maybe stop about 2 feet or so above
the floor. That stuff soaks water like a sponge. I know this from
experience in oct 2005 floods.
My final plan is to use 2" Owens Pink, then wood studded walls with un-
faced fiberglass and a wood planking as the wall surface. (all that
I looked up the building regs from the city and they recommend an
outlet every 6' along the wall.(that sounds like a lot). It did not
mention GFI, but I would install them anyway.
Is the difference between 2" and 1" really going to be noticed ?
Do I need to be concerned what type of floor covering I should be
using right now ? or just wait until the walls are finished and then
look at something like berber (glued) ?
Any comments ?
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