Environmental Engineering Reference
In-Depth Information
(without weep holes and the removal of excess mortar), rain water will be
carried into walls, again causing mold infestation and structural damage.
Timbers on wall interiors are covered by polyethylene plastic, which
serves as a vapor barrier. It is designed to prevent warm, moist air from
passing into building cavities where it may condense and cause structural
damage and mold infestation.
4.
Windows
Windows in dwellings differ in style, size, placement, and materials. They
are designed to keep wind, rain, and snow out, allow light in, and provide
a means of natural ventilation during moderate to hot weather. Windows
are a major source of energy loss because of their thermal energy transmitting
properties. On single-pane windows (found in older houses), moisture on
interior surfaces cools and condenses, causing damage to interior window
surfaces (and in many cases significant mold infestation). Windows also
break the continuity of building cladding. These breaks must be provided
with flashing or be caulked to prevent water from penetrating wall cavities
during heavy rains. Water penetration into wall cavities around windows is
common as houses age and maintenance is neglected.
5.
Flooring
Materials used in both exterior and interior house construction change with
time. In older houses (>40 years), softwood boards were commonly used to
construct floors. In many cases these were overlain with hardwood oak floor-
ing. Because of the high cost of such flooring, it became common to construct
floors using CDX plywood sheeting. Later, contractors used a combination of
softwood plywood sheeting as a base, with
” (1.6 cm) particle board under-
layment above it. This was inexpensive and provided a smooth surface for
attachment of wall-to-wall carpeting. Between 1960 and 1990, over 10 million
homes were constructed in the U.S. using particle board underlayment, a very
potent source of formaldehyde (HCHO). Emissions of HCHO from underlay-
ment have significantly declined in the last decade or so (1988 to 2000). It is
little used in modern site-built construction and has declined to approximately
50% of new manufactured house construction. Particle board flooring has
been displaced by oriented-strand board (OSB), a composite wood material
that has better structural properties and very low HCHO emissions.
The main floor surface of slab-on-grade houses is, of course, concrete,
with wall-to-wall carpeting and other floor coverings overlaying it. This
concrete-ground contact provides a cool surface, which may result in opti-
mal humidity levels for the development of high dust mite populations.
Slab-on-grade substructures also provide (through cracks) a mechanism for
the conveyance of radon and other soil gases (most notably water vapor)
into building interiors.
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6.
Decorative wall and ceiling materials
A variety of materials are used to finish interior walls and ceilings. Base
materials have historically included plaster over wood or metal lath, or
