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The following
information is provided by the National Roofing Contractors
Association (NRCA) as part of their ongoing effort to educate home
and building owners about roofing and roofing contractors.
A new roof
system is a big investment, and you should get a quality roof
system at a fair price from a professional roofing contractor.
Hopefully, this information will make you a more knowledgeable
consumer and, when the time comes, a smart roof system buyer.
 ROOF
SYSTEM COMPONENTS
All
steep-slope roof systems (i.e., roofs with slopes of 25 percent or
more) have five basic components:
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Roof covering:
shingles, tile, slate or metal and underlayment that protect the
sheathing from weather.
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Sheathing:
boards or sheet material that are fastened to roof rafters to
cover a house or building.
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Roof structure:
rafters and trusses constructed to support the sheathing.
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Flashing:
sheet metal or other material installed into a roof system's
various joints and valleys to prevent water seepage.
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Drainage:
a roof system's design features, such as shape, slope and layout
that affect its ability to shed water.
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CHOOSING
A ROOF SYSTEM
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.
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VENTILATION
AND INSULATION ARE KEY
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:
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A gap-free
layer of insulation on the attic floor to protect the house
below from heat gain or loss.
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A vapor
retarder under the insulation and next to the ceiling to stop
moisture from rising into the attic.
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Enough open,
vented spaces to allow air to pass in and out freely.
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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.
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EVEN
ROOFS HAVE ENEMIES
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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TERMS
YOU SHOULD KNOW
Deck/sheathing:
The surface, usually plywood or oriented strand board (OSB), to
which roofing materials are applied.
Dormer:
A small structure projecting from a sloped roof, usually with a
window.
Drip edge:
An L-shaped strip (usually metal) installed along roof edges to
allow water run off to drip clear of the deck, eaves and siding.
Eave:
The horizontal lower edge of a sloped roof.
Fascia:
A flat board, band or face located at a cornice's outer edge.
Felt/underlayment:
A sheet of asphalt-saturated material (often called tar paper)
used as a secondary layer of protection for the roof deck.
Fire rating:
System for classifying the fire resistances of various materials.
Roofing materials are rated Class A, B or C, with Class A
materials having the highest resistance to fire originating
outside the structure.
Flashing:
Pieces of metal used to prevent the seepage of water around any
intersection or projection in a roof system, such as vent pipes,
chimneys, valleys and joints at vertical walls.
Louvers:
Slatted devices installed in a gable or soffit (the underside of
eaves) to ventilate the space below a roof deck and equalize air
temperature and moisture.
Oriented strand board (OSB):
Roof deck panels (4 by 8 feet) made of narrow bits of wood,
installed lengthwise and crosswise in layers, and held together
with a resin glue. OSB often is used as a substitute for plywood
sheets.
Penetrations:
Vents, pipes, stacks, chimneys-anything that penetrates a roof
deck.
Rafters:
The supporting framing to which a roof deck is attached.
Rake:
The inclined edge of a roof over a wall.
Ridge:
The top edge of two intersecting sloping roof surfaces.
Sheathing:
The boards or sheet materials that are fastened to rafters to
cover a house or building.
Slope:
Measured by rise in inches for each 12 inches of horizontal run: A
roof with a 4-in-12 slope rises 4 inches for every foot of
horizontal distance.
Square:
The common measurement for roof area. One square is 100 square
feet (10 by 10 feet).
Truss:
Engineered components that supplement rafters in many newer homes
and buildings. Trusses are designed for specific applications and
cannot be cut or altered.
Valley:
The angle formed at the intersection of two sloping roof surfaces.
Vapor retarder:
A material designed to restrict the passage of water vapor through
a roof system or wall.
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