|Wall Construction & Design
It is necessary to design walls so that moisture vapor does not
enter and condense within the exterior wall cavity. Proper design
will ensure the insulation's thermal efficiency and the overall
structure's performance. Design must provide continuous vapor retarding
equivalent to a rating of 1 perm installed on the living space side
of the insulation.
Vapor retarders are also required on the ground in all crawl
spaces and under concrete slabs. Acceptable products include: 6
mil polyethylene, asphalt impregnated kraft or foil-backed insulation
(tabs must be stapled to the narrow face of the studs, not to the
wide face), vinyl-faced or foil-backed gypsum, sandwich-type kraft
with an asphalt or polyethylene core, or equivalent. Vapor retarding
paints are also available for interior walls.
Slope ground away from structure for a minimum of 3 feet.
Incorporate an overhang or drainage system into the structure
design to prevent water from running down sidewalls.
Both attics and crawl spaces require adequate ventilation. Clothes
dryers must be vented outside; kitchen and bathroom fans are recommended
to vent localized moisture outside.
Attics. Attic vents should provide a minimum of 1 square foot
of net free vent area for every 150 square feet of attic space.
Unrestricted air circulation is best achieved by a combination of
soffit vents and ridge or roof vents.
Crawl space vents should provide a minimum of 1 square foot of
net free vent area for every 25 lineal feet of exterior wall. They
should be placed to allow for cross-ventilation.
Siding Return at Roof (Dormers)
Use flashing, allowing at least a 2-inch clearance between siding
and roof line. Cut edges of siding must be finished in accordance
with finishing instructions described in this guide.
It is recommended to apply cypress siding over standard sheathing
material with maximum stud spacing of 16 inches on-center. Where
building codes permit, siding may be applied over unsheathed walls.
A suitable building or felt paper wind barrier is recommended and
must be used where building codes require.
Foam and Foil-Faced Sheathings. Both rigid foam and foil-faced
sheathings can be vapor barriers. Rigid foam sheathings, however,
offer no resistance to sag caused by the weight of the siding on
the nails. For application of cypress over rigid foam sheathing,
use angular threaded ring shank nails long enough to penetrate at
least 1 inch into framing members. For example, siding over 1-inch
foam requires a 3-inch nail (10d).
click here for more information
on nails & recommended applications.
Note: Wood siding applied over foam sheathing may take on a wavy
appearance if the siding is compressed by nailing with too much