The
Roofing Process: The Basics
While no two roofing jobs are exactly alike, all share one
basic premise: when completed it cannot leak.
A roof system is designed
to shed water, but it takes the right materials and careful workmanship
to build a roof that is durable and leak proof. Start with a solid deck
made of plywood, OSB sheathing, or 1x6 boards; any wood that is not sound
must be removed and replaced before you begin roofing. If you live in
a snowy climate, plan for ice and water shield, which is an asphalt-backed
plastic membrane that stops leaks at the eaves. Next come asphalt paper,
the drip edge, the shingles (with flashing and counter-flashing as needed),
and the hip and ridge caps. All combine to make your roof impervious to
water.
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Quick
Tips |
Roofing
and codes
The key to a good roof is knowing the climate you live in and the
subsequent roof details that are required. A building inspector
or code official can tell you the required fastener spacing for
your area. Ask at your lumberyard about flashing, ice and water
shield membranes, and ridge vents. As for the shingle type, most
codes now require shingles that are labeled as meeting the ASTM
D-3462 or ASTM D-225 standard. Color and style are, of course, up
to you. |
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Roofing
jobs require attention to detail. When properly installed, a quality
roof can last the life of a home. Installed improperly, a roof can
cause a wide range of problems. |
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Estimating
the Project
Whether you hire out or do it yourself, the first step is to measure the
roof and estimate the materials. Roof area is calculated by dividing the
total area into rectangles and squares. Roofers generally add another
10 percent for simple roofs, and 15 percent for roofs with hips and valleys.
The shingles themselves are sold by the "square," which is 100-square-feet.
Eighty shingles will cover one square. Make sure, however, to add the
10 to 15 percent "waste" allowance.
You'll also need four nails per shingle
(six in tornado or high wind country). These are sold by the pound. Asphalt
roofing paper and eaves membrane are sold by the roll, but measured in
lineal feet. Flashing can be purchased in rolls or in pre-folded squares.
Valleys typically require 16-inch-wide flashing, while dormers and sidewall
junctions use one 6x6 or 8x8 inch square of step flashing per course of
shingles. Don't forget to add extra shingles for hip and ridge caps, along
with drip edge and ridge vent. Now you have a fairly clear idea of what
your roof will cost, minus the labor.
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Working
From the Deck Up
Once you've determined that the deck is sound and well fastened, you'll
need to prep it for roofing. Think of a roof as a fish with scales, where
each new layer overlaps the first to keep the water out. First comes the
drip edge, which is nailed along the perimeter of the roof. Next apply
the ice and water shield membrane to overlap the drip edge. Asphalt roofing
paper then covers the whole deck, followed by metal flashing in the valleys.
Next come the shingles (with step flashing applied as you go around chimneys
and skylights), and finally caps for the hips and ridges made with folded
pieces of shingle. If you need ridge vents, put them on after the shingles
but before the ridge caps, following the manufacturer's instructions.
Charting Your Course
For a clean look, it's good to lay out your courses before you begin to
shingle. Use a chalk line to mark straight lines for your courses all
the way up the roof. Begin by measuring one shingle's width up the roof
at each gable end. Snap a line to join the two and proceed up the roof,
snapping lines every 5 inches. This allows you to set the top edge of
each shingle to the line as you go up the roof, and maintain a 5-inch
shingle reveal all the way. Vertical lines spaced every 3 or 6 feet also
help you to keep your tabs lined up. Start your first course with the
shingle edge flush with the drip edge. As you step your courses up the
roof, follow the chalk lines to make sure you are maintaining a nice,
straight pattern.
Details, Details, Details
There are many details that impact the look and performance of your roof.
Shingling the valleys properly and providing adequate flashing and water
shedding detail is a must. Depending on your climate and precipitation
levels, side walls may need higher flashing or extra membrane protection.
Chimneys, vents, and skylights must be flashed and counterflashed to keep
water out. Shingle courses must be cut on an angle along roof hips. Ridges
and hips must be capped to prevent water from entering where two courses
or adjacent roof angles meet. Ridge vents, which allow the roof to breathe
in warm weather, are recommended in many climates. Local codes will tell
you how much roof venting you need.
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