This past winter I found I had a cold wall in my home around my
chimney. I want to replace the fiberglass insulation in that wall
with spray in closed cell foam. I dont want to open up the sheetrock.
It would be much easier to pull off the siding and spray it in from
the outside. Would this be problematic?
YES... It is MUCH easier to deal with sheetrock repairs on
the inside of the wall than it is to cut open a small section
of the outside of the wall, removing the siding, then sheeting
to access the inside of the wall cavity... Then having to
close up the wall, replacing the sheeting then residing all
while making sure it is weather tight...
If you are worried about blending in the wall -- strip off
the sheetrock on that entire wall surface and insulate
the entire wall the same way, rather than one or two
stud bays... The sheetrock repairs to the entire wall
would be easier as your only transitions would be in the
corners and at the edges...
That is exponentially EASIER to deal with than ripping into
the wall of the building to insulate it from the outside in...
Not all spray foam is flammable. There are a number of them out there
that don't support combustion - you remove the flame and the foam
won't burn any more.
To the OP: It is pretty common in these parts to insulate from the
outside as you're planning to do. If you can easily pull some of the
siding (you didn't say what type of siding), then it's certainly worth
looking into. Be aware that code calls out a 2" spacing around the
chimney, and that by adding insulation the requirement for that
spacing is even more important. You mentioned a gas log in a
subsequent post, and that helps matter as the heat produced won't be
as great as a roaring wood fire.
The camera inspection is a very good idea. Unless you can verify that
the stud bays are completely sealed, and the foam won't expand beyond
the stud bays, it's probably a bad idea to spray foam into a wall at a
A problem is you wont know how much to put in, to little and its not
going to fill the cavity, to much and you will Bow the wall. I had a
house done, years later Ive opened several walls and non are fill up
right. The cold could be just from the cold brick itself transfering
in cold, or poor exterior brick to wall air seal.
pros have a minimally expanding foam that wouldnt bow walls.never seen
it DIY and around a chimney its likely not a good idea.
how old is the home / chimney.
does the chimney have a working fireplace on it or just a flue?
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