UNDERSTANDING THE ROOF
OVER YOUR HEAD
There are several
things to consider when selecting a new or replacement roof system. Of
course, cost and durability head the list, but aesthetics and
architectural style are important, too. The right roof system is the one
that balances these four considerations. This page is designed to assist
building owners understand some of the issues involved in determining
what work needs to be done.
All roof systems have
five basic components:
the rafters and trusses constructed to support the sheathing.
the boards or sheet material that are fastened to the roof rafters to
cover a house.
a sheet of asphalt-saturated material used as a secondary layer of
protection for the roof deck.
shingles, tiles, etc., that protect the sheathing from weather.
the features of the roof system's design, such as shape, slope, layout,
etc. that affect its
ability to shed water.
sheet metal or other material laid into the various joints and valleys
of a roof system to prevent water seepage.
VENTILATION IS KEY
One of the most
critical factors in roof system durability is proper ventilation.
Without it, heat and moisture buildup in the attic area combine to cause
rafters and sheathing to rot, roof 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 the life of the roofing
material, 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 floor to protect the house below
from heat gain or loss. A vapor retarder under the insulation next to
the warm ceiling below, to stop moisture from rising into the attic.
Enough open, vented spaces properly located to allow air to pass in and
out freely. A minimum of 1 inch (more space is preferred) between the
insulation and roof sheathing.
The requirements for
proper attic ventilation may vary greatly, depending on where the home
is located, as well as the home site's conditions, such as exposure to
the sun, shade, and atmospheric humidity. Nevertheless, the general
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 (i.e.,
soffits) and near the ridge.
ROOFS HAVE ENEMIES
Heat and ultraviolet rays cause roofing materials to deteriorate over
time. The deterioration can occur faster on the sides facing west or
south. Rain: When water gets underneath shingles, shakes, or other
roofing materials, it can work its way to the deck and cause the roof
structure to rot. The extra moisture encourages mildew and rot elsewhere
in the house, including damaged
insulation, and electrical system.
High winds can lift the edges of shingles (or other roofing materials)
and force water—and debris—underneath them. Very high winds can do
Snow and ice:
Melting snow often refreezes at the roof's overhang (where the surface
is cooler), forming an ice dam and blocking proper drainage into the
gutter. Instead, the water backs up under the shingles 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 torn off
Condensation can result from the buildup of relatively warm,
moisture-laden air. Moisture in a poorly ventilated attic promotes decay
of the wood sheathing and rafters, possibly destroying the roof
structure. The solution may be to increase attic ventilation through the
use of larger or additional vents so the attic air temperature will be
closer to the outside air temperature.
Moss and algae:
Moss can grow on wood shingles and shakes if they are kept moist by poor
sunlight conditions or bad drainage. Once it grows, moss holds even more
moisture to the roof surface, causing rot, and its roots actually work
their way into the wood. Algae also grows in damp, shaded areas on wood
or asphalt shingle roof systems. Besides creating an ugly black-green
stain, algae can retain moisture, causing rot and deterioration. Trees
and bushes should be trimmed away from the house to eliminate damp,
shaded areas, and gutters should be kept
clean to ensure good
Trees and leaves:
Tree branches touching the roof will scratch and gouge roofing materials
as they are blown back and forth by the wind. Falling branches from
overhanging trees can amage—or even puncture—shingles and other roofing
materials. Leaves on the roof system's surface retain moisture and cause
rot, and leaves in the gutters block drainage.
Missing or torn
The key to a roof system's effectiveness is complete protection. When
shingles are missing or torn off, the roof structure and interior of the
home are vulnerable to water damage and rot. The problems are likely to
spread—nearby shingles are easily ripped or blown away. Missing or torn
shingles should be replaced as soon as possible. Shingle deterioration:
When shingles get old and worn out, they curl, split, and lose their
waterproofing effectiveness. Weakened shingles are easily 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,
and it should be replaced as soon as possible.
Many apparent roof leaks really are flashing leaks. Without good, tight
flashings around chimneys, vents, skylights, and wall/roof junctions,
water can sneak into the house and cause damage to the walls, ceilings,
insulation, and electrical system. Flashings should be checked as part
of a twice-yearly roof inspection and gutter cleaning.
TYPES OF ROOF COVERINGS
possess an overwhelming share of the Canadian residential roofing
market—can be reinforced with either organic or fiberglass materials.
Although shingles reinforced with organic felts have been around much
longer, fiberglass-reinforced products now dominate the market. Organic
shingles consist of a cellulose-fiber (i.e., wood) base that is
saturated with asphalt and coated with colored mineral granules. To
fight fungus growth in warm, wet climates, they are available with
special algaecide granules.
consist of a fiberglass mat, top-and-bottom layers of asphalt, and
mineral granules. Typically, a fiberglass mat offers greater durability,
but its manufacture is important.
The fire resistance of
asphalt shingles, like most other roofing materials, is categorized by
Underwriters Laboratories Inc. (UL) Class A, B, or C. Class A is the
most fire-resistant, while Classes B and C have less fire resistance.
Generally, most fiberglass shingles have Class A fire ratings, and most
organic shingles have Class C ratings. UL Class A fire ratings are
available for certain products that incorporate a factory-applied,
fire-resistant treatment. A shingle's reinforcement will have little
effect on its appearance. Both 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 either organic or fiberglass products to protect against algae
attack, a common problem in hot, humid climates. Both types of shingles
also are available in a variety of colors.
and shakes are made from cedar, redwood, southern pine, and other woods.
Shingles are machine-sawn; shakes are hand-hewn and rougher looking.
Their natural look is popular in California, the Northwest, and parts of
the Midwest. A point to consider: Some local building codes limit their
use because of concerns about fire resistance. Many wood shingles and
shakes only have a UL Class C fire rating (or no rating at all).
Tile—clay or concrete—is
a durable but fairly expensive roofing material. "Mission-style" and
"Spanish" 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. Note: Tile
is heavy. If you are replacing another type of roof system with tile,
you will need to verify that the structure will support the load. Slate
is quarried in places such as Vermont, New York, Pennsylvania, Virginia,
and Canada. It comes 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 skill and experience. Many old homes in the Northeast still are
protected by this long-lasting roofing material.
primarily thought of as a commercial roofing material, and has been
found to be an attractive roofing alternative for home owners. There are
a variety of metal shingles intended to simulate traditional roof
coverings, such as wood shakes, shingles, and tile. Apart from metal
roofing's longevity, metal shingles are relatively lightweight,
typically have a Class A fire rating, have a greater resistance to
adverse weather, and can be aesthetically pleasing.
roof products simulate various types of traditional roof coverings, such
as slate and wood shingles and shakes. A point to consider: Although
synthetic roof products may simulate the appearance of traditional roof
coverings, they do not necessarily have the same properties.
We recommend that you
look at full-size samples of the proposed product, along with
manufacturers' brochures, or visit a building that is roofed with that
product before making a buying decision.
Q. How can I know when
a roof system has problems?
A. All too often, roof system problems are discovered
after leaking or other serious damage occurs. Periodic (twice-a-year)
inspections often can uncover cracked, warped or missing shingles; loose
seams and deteriorated flashings; excessive surface granules
accumulating in the gutters or downspouts; and other visible signs of
roof problems. Indoors, look for cracked paint, discolored plasterboard,
and peeling wallpaper as signs of damaged roof areas.
Q. What are my options
if I decide to re-roof?
A. You have two basic options: You can choose a complete
replacement of the roof system, involving a tear-off of the old roof, or
a re-cover over the existing roof, involving only the installation of a
new membrane and surfacing. If you've already had one re-cover over your
original roof, check with a professional roofing contractor to see if
your deck can support a second re-cover.
Q. My roof leaks. Do I
need to have it totally replaced?
A. Not necessarily. Leaking can result because some
flashings have come loose or a section of the roof system has been
damaged. A roof system failure, however, generally is irreversible and
results from improper installation or choice of materials or from the
installation of a roof system inappropriate for the building.
Q. Can't I just do the
A. Most work should not be do-it-yourself. Professional
roofing contractors are trained to safely and efficiently repair or
replace a roof system. Novices can harm a roof with improper roofing
techniques and severely injure themselves by falling off or even through
a roof in need of repair or replacement. Home owner maintenance should
be confined to roof system inspections in the fall and spring to check
for cracked or curling shingles and to cleaning rain gutters filled with
dead leaves and other debris. If you must see the roof for yourself, use
a firmly braced or tied-off ladder equipped with rubber safety feet.
Wear rubber-soled shoes and stay on the ladder (and off the roof), if
Q. How long can I
expect my roof system to last?
A. The condition and lifespan of your roof system will
depend on the type of roof system you have, the effects of your local
environment, and the maintenance the roof system has received. Asphalt
shingles generally last 15 to 20 years; wood shingle/shakes, 10 to 40
years; clay/concrete tiles, 30+ years; slate, 30 to 100 years; and metal
roofing, 25 to 50+ years.
manufacturers offer a variety of warranties on their products. Take a
close look at those warranties to see what responsibilities and
financial obligations they will assume if their products fail to reach
their expected lifetimes.
Q. What will a new roof
A. The price of a new roof system varies widely,
depending on the material selected, the contractor doing the work, the
home itself, location of the home or building, local labor rates, time
of year, and more. Keep in mind that cost is only one factor, and it
must be balanced with the quality of the materials and workmanship. For
each roofing material, there are different grades—and corresponding
prices. Plus, there are a variety of styles and shapes. You need to look
at the full product range and make a choice based on your budget and
Roofing terms you
The surface—usually plywood or oriented-strand board (OSB)—to which
roofing materials are applied.
A small structure projecting from a sloped roof, usually with a window.
An L-shaped strip (usually metal) installed along the edges of the roof
to allow water runoff to drip clear of the deck, eaves, and siding.
The horizontal lower edge of a sloped roof.
A flat board, band, or face located at the outer edge of the cornice.
A sheet of asphalt-saturated material used as a secondary layer of
protection for the roof deck.
UL system for classifying the fire resistance of various materials.
Roofing materials are rated "Class A," "B," or "C," with "A" materials
having the highest resistance to fire originating outside the
Sheet metal used to prevent the seepage of water around any intersection
or projection in a roof, such as vent pipes, chimneys, valleys, and the
joints at vertical walls.
Slatted devices installed in the gable or soffit (the underside of the
eaves) to ventilate the
space below the roof deck and equalize air temperature and moisture.
Oriented-strand board (OSB):
Roof deck panels (4 feet x 8 feet) made of narrow bits of wood, laid
down lengthwise and crosswise in layers, held together with resin
"glue." Often used as a substitute for plywood sheets.
Vents, pipes, stacks, chimneys—anything that sticks up through the roof
The supporting framing to which the roof deck is attached.
The inclined edge of a roof over a wall.
The top edge of two intersecting, sloping roof surfaces.
The boards or sheet materials that are fastened to the roof's rafters to
cover the house.
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.
The common measurement for roof area is—100 square feet (10 feet x
The horizontal element that spans the space between the eave and the
wall of the building. The overhang area of the roof that also usually
provides the roof air venting.
The engineered components that have supplemented rafters in many newer
houses. They are designed for specific applications and cannot be cut or
altered in any way.
The angle formed at the intersection of two sloping roof surfaces.
A material designed to restrict the passage of water vapor through a
roof system or wall.