Soon I will be removing a lot of the wood lap siding on our 1938 house
and replacing it with fiber cement lap siding. The wood siding is in
poor condition and we are adding a room on the back of the house which
would make it impossible to weave in the fiber cement with the old wood
siding. Anyhow, I'd like to add insulation to the walls from the
outside while I have the siding removed. Currently the walls are not
insulated. I live in northern California and the walls are standard 2 x
4 studs, no plywood sheathing between the studs and the siding. I was
planning on using R-13 batt insulation but don't know which type-
unfaced, kraft paper or encapsulated in plastic. My preference would be
in order- encapsulated, kraft paper and then unfaced. I plan on
covering the insulation with either house wrap or 15 lb. roofing paper.
Is there any reason not to use the plastic encapsulated insulation,
stapled to the outside of the framing studs and then cover it with
either Tyvek or building paper and then the Hardiplank lap siding? The
interior walls are lath and plaster. Thanks.
Not positive but I always thought vapor barrier goes to occupied side.
Reading below shows me correct for my area. It could be different for
From Owens Corning, everything you wanted to know.
Faced and Unfaced Insulation
"Facing" refers to material applied to one side of a batt of insulation to
prevent moisture from passing through the insulation and condensing on
exterior or interior walls. This facing is called a vapor retarder.
Insulation that does not have a vapor retarder applied to it is called
Showers, cooking, washing and even breathing can put a surprising amount of
moisture into the home-from 5 to 10 pounds a day! Washing and drying clothes
indoors can add another 30 pounds. Vapor retarders help control the amount
of moisture passing through insulation and collecting inside exterior walls,
ceilings and floors.
In the winter, any moisture that passes through to these surfaces can
accumulate and condense on the cold inner sides of exterior surfaces.
Eventually, this condensation may blister the outside paint, form stains on
drywall ceilings or walls, or even damage your house structure.
Whatever vapor retarder you choose, remember this important rule of thumb:
In heating climates, the vapor retarder is always installed toward the
warm-in-winter side (living area) of the house.
(In the Gulf Coast and Florida, local building practice may not call for an
interior vapor retarder, or may call for the vapor retarder to be installed
toward the outside in exterior walls. See installation instructions on
There are three types of vapor retarders:
Kraft paper attached to insulation with a thin coat of asphalt.
Foil-backed paper attached with a thin coat of asphalt.
A separate 4- to 6-mil polyethylene film applied over installed insulation.
Note: Never leave faced insulation exposed. The facings on kraft- and
foil-faced insulation will burn and must be installed in substantial contact
with an approved ceiling, wall, or floor construction material to help
prevent the spread of fire in the wall, ceiling or floor cavities.
Insulating Irregular Spaces
Insulation must be gently fitted around pipes, wiring, electrical boxes and
heating ducts - compressing the insulation will reduce its R-value. There
should be no gaps or spaces between insulation pieces. These are places
where energy would be lost for the life of the house.
[vapor barrier goes on which side of insulation?]
Where it gets really confusing to me is areas that heat in the winter,
and A.C. in the summer. The "warm side" changes with the season. In my
area the vapor barrier goes on the inside even though (IMHO) the warm
side is outside for more of the year, and the inside air while heating
is typically _very_ dry.
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sdbuse1 on mailhost bigfoot.com
In northern California I would guess you should have the vapor barrier
towards the inside. Check local codes or local builders. I would make sure
it does have a vapor barrier. That leaves out the encapsulated stuff as the
plastic is intentionally compromised to allow ventilation.
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