Environmental Engineering Reference
In-Depth Information
Roof construction also reflects resource availability and cultural preferences.
In new U.S. residential construction, roofs are typically constructed with
oriented-strand board decking on wood trusses. Decking is then covered
with asphalt felt and shingles. In the southwestern U.S., as in some other
parts of the world (Europe, Southeast Asia, Japan, Australia), terra cotta
roofing is preferred. In some parts of the U.S. (South) and Australia, painted
galvanized steel is the most common roofing material.
Roof construction and materials used are important. The roof must carry
away water without leakage, lest significant internal structural damage and
mold infestation occur. In cold, snowy climates, the roof must be strong
enough to support the weight of heavy snow. In regions with severe storms,
roofs must be securely anchored lest they experience serious damage. The
cavity between the roof and ceiling timbers must be adequately ventilated
to prevent the build-up of excessive moisture, which in cool/cold climates
may result in condensation and even freezing. Poorly ventilated attics may
result in structural damage and mold infestation.
3.
Sidewalls and walls
The exterior sidewalls of dwellings are typically constructed using structural
timbers, fiberglass insulation, Styrofoam or polyurethane sheeting to provide
additional low-cost insulation, oriented-strand board sheeting in corners and
around windows to provide extra strength, an external semipermeable mem-
brane (e.g., Tyvek), and one or more types of external cladding. Typical cladding
includes, or has included, aluminum or vinyl siding, wood or fibrocement
weatherboard, stucco over concrete block, and brick or stone veneer. Cladding
is an important factor in protecting the building from the vagaries of weather
and climate. All cladding types indicated above provide reasonable protection
from wind, water, and snow. From a structural standpoint, houses constructed
with brick/stone veneer are less prone to damage from wind gusts which can
tear off small to large pieces of vinyl and aluminum siding. Wood weatherboard
must be painted repeatedly and, with time, can deteriorate as a result of weath-
ering and inadequate maintenance. In many older houses, wood weatherboard
was painted with lead-based paint and represents a potentially significant
source of lead contamination of the soil surrounding the building, as well as
interior dust. Old weatherboard-clad houses are often a major public health
concern because of their potential to cause lead poisoning in young children.
As in the story of the three little pigs, an all-brick or stone house would
seem to provide the best shelter. However, such houses are not without prob-
lems. Brick/stone veneer houses constructed on unstable soils develop small
to large settlement cracks which provide an avenue for rain to enter building
cavities. Here both liquid water and water vapor can cause structural damage
and mold infestation. In the absence of settlement cracks, many brick/stone
veneer facades pass water through porous mortar and brick, and through
small holes. If constructed properly, rain water will drain down the interior
surface of the mineral facade and seep out through properly functioning weep
holes at the bottom. If brick/stone veneer facades are poorly constructed
