My son and I are building him a house, framing the walls with 2x6
studs and sheathing with 1/2" Advantec. The house is in a cold region
and we're insulating the walls with 5 1/2" R21 fiberglass batts and 1"
styrofoam bridging the studding on the inside walls (with 1/2"
drywall applied over the styro). We'll caulk the edges of the
styrofoam and seal the joints with tape.
However, we're concerned that any moisture that may penetrate the stud
bays will condense on the cold, inside surface of the Advantec,
possibly leading to the formation of mold.
Question: Is there a proven, relatively inexpensive, anti-mold
construction spray that we could use in the stud bays prior to
insulating that will inhibit the growth of mold/fungus over time? Is
this step necessary?
First off, I have never heard of a mold preventative spray.
Fiberglass insulation itself will mold---how would you spray that so
it penetrated the batts? If you were going to plan on letting a wall
assembly get wet, I'd suggest you better use treated studs covered
with treated plywood.
I believe that the approach should be to prevent water and vapor
intrusion. First, you need to be absolutely anal about your exterior
drainage. Windows and doors should be flashed, Building paper should
be applied "shingle style" to shed water, your siding should be
carefully detailed to prevent water intrusion. You also need to be
anal about your interior vapor barrier to prevent moisture from inside
the house getting into the stud cavities.
An approach that many builders are taking where I live (Northern MN)
is to apply a layer of foam to the outside rather than the inside.
Part of the reasoning for this is that the foam outside will raise the
temperature of the sheathing/stud cavity and make condensation less
likely. One concern I'd have about this approach is that you would
need to be sure that your stud cavities are dry before you close them
up. (probably a good policy anyway).
Why are you using Advantec?
Excellent answer. I would any add that the vapor retarder in the inside
shoud be 5x more that the exterior. Adding the foam to the exterior is more
effective, and would offer a better shear racking value to the braced wall
line (exterior walls).
Thanks for your reply. We used Advantec because it doesn't
delaminate under wet conditions (such as downpours during
construction), and because it's manufactured in Maine, where we live.
We've already put 20 squares of cedar shingles to the exterior walls,
using Grace Ice and Water shielding around the door and window
openings, and carefully lapping 30# felt paper everywhere else.
We decided not to insulate the exterior of the building since it
seemed a lot easier for our father and son crew to apply it across the
interior surface of the studding, considering the fact we'd need to
strap the exterior insulation to apply the cedar shingles. We were
hoping to spray the bare stud bays with an anti-mold solution and let
it dry before we installed the fiberglass batts.
We'll be "anal" about sealing the styrofoam across the interior
walls, but we hoped there might be an affortable way to "inoculate"
the stud bays against any possible mold formation.
Mold is generally inhibited by the presence of salts of metals such as
copper and zinc. I know companies like Dow Chemical (e.g. Amical),
BASF, and others have materials available that are used for wood
treatment or use in polymers and will preserve wood for many years
even when buried in the ground. I would check at their websites or
make a couple of calls for anti-fungals that are of limited water
solubilty and see if I could get some directly from the company then
make up an alcohol solution and spray it on the surfaces I want
protected. If that's not possible due to EPA regulations I'd see if
they could recommend someone who sells products with these actives.
If all else fails I (personal option - not a reccomendation) would go
to a chemical supply company and buy some copper sulfate (blue stone)
and make up a dilute solution and spray it on the areas that will need
protection. Copper sulfate, while it is water soluble, should remain
in mostly dry areas for many years as long as there is not water
actually flowing over the surface.
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