Environmental Engineering Reference
In-Depth Information
Figure 6.8
Thermal bridge. (From Lstiburek, J. and Carmody, J.,
Moisture Control
Handbook
, Van Nostrand Reinhold (John Wiley & Sons), New York, 1992. With
permission.)
loss. The movement of wind through soffit vents may result in reduced
insulation effectiveness and even blow the insulation inward. Cold spots in
such areas contribute to condensation and mold infestation.
3. Thermal bridges
Localized cooling of interior building surfaces may occur on thermal bridges.
These are areas of relatively high heat conductivity in building envelopes.
Examples include uninsulated window lintels, edges of concrete floor slabs,
and, most commonly, wood studs in exterior framed walls of residences and
other buildings where insulation is installed in wall cavities. Since the wood
stud has a higher thermal conductivity than insulation, it provides a pathway
for heat loss and localized cold spots on exterior walls. These cold spots can
result in high localized relative humidities and potential sites for mold
growth. Thermal bridges are illustrated in
Figure 6.8
.
4. Wall cavities
Condensation occurs when warm, moist, interior air moves into wall cavities
where it contacts cold surfaces. Such concealed condensation is common in
poorly constructed, poorly insulated walls. However, it may also occur in
well-constructed walls (even with vapor barriers). In cool/cold climates, the
first condensing surface is typically the interior surface of the exterior non-
insulating sheeting (typically plywood or oriented-strand board). In
warm/hot climates, the first condensing surface is the exterior side of the
interior gypsum board or finish material. If the interior is being cooled, warm,
moist outdoor air condenses on contact with interior finishing materials,
resulting in mold growth on the back of such materials as vinyl wallpaper.
5. Plumbing
Condensation commonly occurs on uninsulated plumbing lines and fixtures.
Uninsulated cold water lines in a relatively humid environment can result
in considerable “sweating” and subsequent wetting of adjacent materials.
Sweating occurs on toilet fixtures as well. Such sweating may cause both
structural damage and mold infestation.
