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 There
are a number of things to consider when selecting a new
roof system. Of course, cost and durability head the
list, but aesthetics and architectural style are
important, too. The right roof system for your home or
building is one that balances these five considerations.
The following roofing products commonly are used for
steep-slope structures.
Asphalt shingles possess an
overwhelming share of the U.S. steep-slope roofing
market and can be reinforced with organic or fiberglass
materials. Although asphalt shingles reinforced with
organic felts have been around much longer,
fiberglass-reinforced products now dominate the market.
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Organic shingles
consist of a cellulose-fiber (i.e., wood) base that
is saturated with asphalt and coated with colored
mineral granules.
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Fiberglass shingles
consist of a fiberglass mat, top-and-bottom layers
of asphalt, and mineral granules.
Asphalt
shingles' fire resistances, like most other roofing
materials, are categorized by Class A, B or C. Class A
signifies the most fire-resistant; Classes B and C
denote less fire resistance. Generally, most fiberglass
shingles have Class A fire ratings, and most organic
shingles have Class C ratings.
A shingle's reinforcement has little effect on its
appearance. Organic and fiberglass products are
available in laminated (architectural) grades that offer
a textured appearance. Zinc or copper-coated ceramic
granules also can be applied to organic or fiberglass
products to protect against algae attack, a common
problem in warm, humid parts of the United States. Both
types of shingles also are available in a variety of
colors.
Regardless of their reinforcing type and appearance,
asphalt shingles' physical characteristics vary
significantly. When installing asphalt shingles, NRCA
recommends use of shingles that comply with American
Society for Testing and Materials (ASTM) standards-ASTM
D 225 for organic shingles and ASTM D 3462 for
fiberglass shingles. These standards govern the
composition and physical properties of asphalt shingles;
not all asphalt shingles on the market comply with these
standards. If a shingle product complies with one of
these standards, it is typically noted in the
manufacturer's product literature and on the package
wrapper.
Wood
shingles and
shakes are made
from cedar, redwood, southern pine and other woods;
their natural look is popular in California, the
Northwest and parts of the Midwest. Wood shingles are
machinesawn; shakes are handmade and rougher looking. A
point to consider: Some local building codes limit the
use of wood shingles and shakes because of concerns
about fire resistance. Many wood shingles and shakes
only have Class C fire ratings or no ratings at all.
However, Class A fire ratings are available for certain
wood shingle products that incorporate a
factory-applied, fire-resistant treatment.
Tile —clay or
concrete—is a durable roofing material. Mission and
Spanish-style round-topped tiles are used widely in the
Southwest and Florida, and flat styles also are
available to create French and English looks. Tile is
available in a variety of colors and finishes. Tile is
heavy. If you are replacing another type of roof system
with tile, you will need to verify that the structure
can support the load.
Slate is quarried
in the United States in Vermont, New York, Pennsylvania
and Virginia. It is available in different colors and
grades, depending on its origin. Considered virtually
indestructible, it is, however, more expensive than
other roofing materials. In addition, its application
requires special skill and experience. Many old homes,
especially in the Northeast, still are protected by this
long-lasting roofing material.
Metal , primarily
thought of as a low-slope roofing material, has been
found to be a roofing alternative for home and building
owners with steep-slope roofs. There are two types of
metal roofing products: panels and shingles. Numerous
metal panel shapes and configurations exist. Metal
shingles typically are intended to simulate traditional
roof coverings, such as wood shakes, shingles and tile.
Apart from metal roofing's longevity, metal shingles are
relatively lightweight, have a greater resistance to
adverse weather and can be aesthetically pleasing. Some
have Class A fire ratings.
Synthetic
roofing products simulate various traditional
roof coverings, such as slate and wood shingles and
shakes. However, they do not necessarily have the same
properties.
Before making a buying decision, NRCA recommends that
you look at full-size samples of a proposed product, as
well as manufacturers' brochures. It also is a good idea
to visit a building that is roofed with a particular
product.
One of the
most critical factors in roof system durability is
proper ventilation. Without it, heat and moisture build
up in an attic area and combine to cause rafters and
sheathing to rot, shingles to buckle, and insulation to
lose its effectiveness.
Therefore, it is important never to block off sources of
roof ventilation, such as louvers, ridge vents or soffit
vents, even in winter. Proper attic ventilation will
help prevent structural damage caused by moisture,
increase roofing material life, reduce energy
consumption and enhance the comfort level of the rooms
below the attic.
In addition to the free flow of air, insulation plays a
key role in proper attic ventilation. An ideal attic
has:
- A gap-free
layer of insulation on the attic floor to protect
the house below from heat gain or loss.
- A vapor
retarder under the insulation and next to the
ceiling to stop moisture from rising into the attic.
- Enough
open, vented spaces to allow air to pass in and out
freely.
- A minimum
of 1 inch between the insulation and roof sheathing.
The
requirements for proper attic ventilation may vary
greatly, depending on the part of the United States in
which a home or building is located, as well as the
structure's conditions, such as exposure to the sun,
shade and atmospheric humidity. Nevertheless, the
general ventilation formula is based on the length and
width of the attic. NRCA recommends a minimum of 1
square foot of free vent area for each 150 square feet
of attic floor—with vents placed proportionately at the
eaves (e.g., soffits) and at or near the ridge.
A roof
system's performance is affected by numerous factors.
Knowing about the following will help you make informed
roof system buying decisions:
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Sun: Heat and ultraviolet rays cause
roofing materials to deteriorate over time.
Deterioration can occur faster on the sides facing
west or south.
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Rain: When water gets underneath shingles,
shakes or other roofing materials, it can work its
way to the roof deck and cause the roof structure to
rot. Extra moisture encourages mildew and rot
elsewhere in a house, including walls, ceilings,
insulation and electrical systems.
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Wind: High winds can lift shingles' edges
(or other roofing materials) and force water and
debris underneath them. Extremely high winds can
cause extensive damage.
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Snow and ice: Melting snow often refreezes
at a roof's overhang where the surface is cooler,
forming an ice dam. This blocks proper drainage into
the gutter. Water backs up under the shingles (or
other roofing materials) and seeps into the
interior. During the early melt stages, gutters and
downspouts can be the first to fill with ice and be
damaged beyond repair or even torn off a house or
building.
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Condensation: Condensation can result from
the buildup of relatively warm, moisture-laden air.
Moisture in a poorly ventilated attic promotes decay
of wood sheathing and rafters, possibly destroying a
roof structure. Sufficient attic ventilation can be
achieved by installing larger or additional vents
and will help alleviate problems because the attic
air temperature will be closer to the outside air
temperature.
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Moss and algae: Moss can grow on moist wood
shingles and shakes. Once it grows, moss holds even
more moisture to a roof system's surface, causing
rot. In addition, moss roots also can work their way
into a wood deck and structure. Algae also grows in
damp, shaded areas on wood or asphalt shingle roof
systems. Besides creating a black-green stain, algae
can retain moisture, causing rot and deterioration.
Trees and bushes should be trimmed away from homes
and buildings to eliminate damp, shaded areas, and
gutters should be kept clean to ensure good
drainage.
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Trees and leaves: Tree branches touching a
roof will scratch and gouge roofing materials when
the branches are blown by the wind. Falling branches
from overhanging trees can damage, or even puncture,
shingles and other roofing materials. Leaves on a
roof system's surface retain moisture and cause rot,
and leaves in the gutters block drainage.
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Missing or torn shingles: The key to a roof
system's effectiveness is complete protection. When
shingles are missing or torn off, a roof structure
and home or building interior are vulnerable to
water damage and rot. The problem is likely to
spread-nearby shingles also are ripped easily or
blown away. Missing or torn shingles should be
replaced as soon as possible.
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Shingle deterioration: When shingles are
old and worn out, they curl, split and lose their
waterproofing effectiveness. Weakened shingles
easily are blown off, torn or lifted by wind gusts.
The end result is structural rot and interior
damage. A deteriorated roof system only gets worse
with time-it should be replaced as soon as possible.
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Flashing deterioration: Many apparent roof
leaks really are flashing leaks. Without good, tight
flashings around chimneys, vents, skylights and
wall/roof junctions, water can enter a home or
building and cause damage to walls, ceilings,
insulation and electrical systems. Flashings should
be checked as part of a biannual roof inspection and
gutter cleaning.
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