Controlling
Moisture
High humidity output from washers, dryers, showers,
kitchens and other sources, combined with today's
energy-efficient construction, can result in a build
up of interior moisture vapor. This vapor migrates
through the fabric of a building from the warm interior
to the cold exterior, and when it condenses to water
can cause structural damage to sidings and finishes.
Vapor barriers installed on the warm side of
the wall prevent most of the migration of moisture
vapor but they have disadvantages. Residual vapor
must be allowed to escape to the outside. Building
paper installed on the outside face of the sheathing
helps prevent rain and snow from penetrating the
walls and also allows the escape of moisture vapor.
Proper wall construction includes the use of
gas permeable paper and vapor barriers (see Figure
3). These are extremely effective in helping to
prevent moisture problems.
Ground Clearance
Keep the lowest edge of siding at least
6" off the ground and coat end grain at the
bottom of vertical siding with water repellant.
Caulking
Thorough caulking of all joints is recommended
including butt joints and where siding contacts
openings or trim. Use only non-hardening caulks
such as polyurethane, polysulfide or latex-silicone.
Pure silicon caulks do not work well on cedar
and are not recommended.
Do not reduce the siding overlap recommendations
given in the installation sections of this publication.
To do so could result in damage from wind-driven
water.
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