Re: GBlist: The foam in the wall gang
Thu, 13 Feb 1997 11:15:13 -0500 (EST)


Greg wrote " I would be concerned about air quality issues raised by the wood
stove in
addition to the foamboard. Considering combustion air and adeqate removal of
the products of combustion would be part of the process. I would also
consider the potential for moisture condensation in the cavity behind the
insulation. Addressing basic building construction concerns such as these is
often serendipitous."

I'm not sure which side of the insulation you concerned may develop
condensation. I have two general thoughts. The first is that it is alright
for concrete block and extruded styrene foam board to get wet. I'd be more
concerned if the water bridged from the condensation plane into the interior
where it wetted some cellulose based material (lumber of sheetrock for
example). Ordinary drainage detailing will prevent that. Second, the
moisture dynamics in a wall that is block-extruded-styrene-block depends on
outdoor conditions (climate), indoor conditions (heating or cooling mode) ,
whether the wall is all above, all below or partially below grade, and the
moisture sources inside and outside. In most conditions, the wall should
have little risk of condensation. However, I can imagine a moisture
condensation problem occurring in this type of wall in an air conditioned
building (hot outside-cool inside), a rain wetted exterior wall with direct
sun and vinyl wall paper on the interior (if the building is running negative
that helps a bunch too). In fact, I don't have to imagine it, I can recall
it. This problem is not intrinsic to block-foam-block walls however. I
can't think of one that couldn't be fairly easily avoided.
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