Asphalt
shingles are the most commonly used type of roof covering for pitched
roofs on homes. The overlapping design of the installed shingles provides
a double layer of protection as the water flows down the roof slope to
the roof edge. Asphalt shingles, also known as composition shingles, are
so widely used because of their moderate cost, light weight (compared
to many other roofing products), durability, and ease of installation.
Asphalt shingles are surfaced on the top side with mineral granules to
provide protection from the elements and a level of fire resistance. Asphalt
shingles are available in a variety of colors, weights and patterns. Regular
weight asphalt shingles generally have an economic life span of 16-20
years; heavyweight shingles are sold as 30-40 year shingles. Roof surfaces
with full southern exposure tend to experience a shorter life span.
The installation of an asphalt roof involves more than just the roofing
itself. The shingles are normally installed over solid wood or composite
sheathing, which is nailed to the roof framing. A water-resistant saturated
felt underlayment is typically rolled out over the sheathing before the
shingles are applied. In cold climates, a special rubberized membrane
is installed along the eave to provide extra protection from ice dams
and water backup. Eave or gable edge flashing is also commonly used in
many areas.
Flashings are also required at all roof penetrations. Flashings are angled
barriers designed to divert water where a roof plane changes (valley)
or at the roof surfaces around a roof protrusion (vent pipe, chimney,
etc.). Poorly applied flashings open and allow water to penetrate the
roof surface. If valley flashings are too narrow, backed-up water can
find its way under the roofing materials. Most reported roof leaks are
in fact flashing leaks.
Many homes require a roof drainage system to control water runoff from
the roof and prevent damage to exterior elements and water seepage into
subgrade areas. In most cases, metal or plastic gutters are hung along
the eave of the roof and carry the water to downspouts, which discharge
the water at ground level.
Some gutters are made of wood or are built-in as part of the eave framing
and lined with metal. Built-in or "Yankee" gutters are more often found
on older homes and are prone to damage and eventual leakage as they age.
Downspouts, which are made of metal or vinyl, must be large enough to
handle all the water collected by the gutters in a reasonable time period.
At least one downspout is usually needed for each 25-30 feet of gutter
length.
Gutters and downspouts also help reduce erosion along the foundation and
protect steps and walkways from unwanted water (and ice) buildup. All
downspouts must be piped away from the house foundation to prevent water
accumulation and eventual seepage into the foundation. If underground
lines are present, be certain to keep them unclogged and flowing. The
major cause of the failure of roof drainage systems is blockage due to
leaves, twigs and sediment buildup. Regular cleaning of gutters, especially
in spring and fall, is essential. Coating of gutter interiors and sealing
of seams may be needed in some cases to prolong their useful life and
prevent leakage.
To obtain maximum life from your asphalt shingle roof:
• Keep trees trimmed to prevent damage to the roof surface
from branches or falling limbs.
• Check the roof surface annually for obvious damage, lifted
or worn shingles. Pay particular attention to valley areas and flashings.
• Have missing or damaged shingles promptly replaced.
• Periodically check the underside of the roof for signs of
leakage or damage, especially around vent pipes and chimneys. Also look
for any signs of mildew or mold, which may be associated with roof leakage
or ventilation problems.
• Maintain good ventilation in the attic even in winter months.
Poor attic ventilation can cause damage to a roof structure. Additional
vents or an automatic vent fan may be required.
• In areas with heavy snowfall and subfreezing temperatures,
be alert for ice dams which form along the eaves. Ice dams can cause water
damage to the interior ceilings and walls.
If isolated portions of a roof show some wear, or if storm damage occurs,
repairs can normally be accomplished without much difficulty. But regardless
of the type of materials used, eventually all roofing will require replacement.
If it is badly worn or just suffering from overall old age, limited repairs
won't practically extend its service life. |