The Metal Wizards
MW ROOFING
MW is pleased to provide you with
this information as part of our ongoing effort to educate
home and building owners
about roofing and roofing contractors.
We hope this information will make you a more knowledgeable consumer and, when the
time comes, a smart roof system buyer.
A new roof system is a big investment. We want to help you get a quality roof system
at a fair price from a professional roofing contractor.
Roof system components
All steep-slope roof systems (i.e., roofs with slopes of 25 percent or more) have
five basic components:
- Roof covering: shingles, tile, slate or metal and under layment that protect
the sheathing from weather.
- Sheathing: boards or sheet material that are fastened to roof rafters to
cover a house or building.
- Roof structure: rafters and trusses constructed to support the sheathing.
- Flashing: sheet metal or other material installed into a roof system's various
joints and valleys to prevent water seepage.
- Drainage: a roof system's design features, such as shape, slope and layout
that affect its ability to shed water.
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.
consist of a cellulose-fiber (i.e., wood)
base that is saturated
with asphalt and coated with colored mineral granules.
consist of a fiberglass mat, and fiberglass 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,the 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 machine sawn; 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.
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, the 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.
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:
- 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. The 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.
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: Sun:Heat and ultraviolet rays cause roofing materials to deteriorate over
time. 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 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
Commonly asked questions
Q:How can a home owner recognize 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
system 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 reroof?
A:You have two basic options: You can choose a complete replacement of the
roof system, involving a tear-off of your existing roof system, or re-cover the
existing roof system, involving only the installation of a new roof system. If you've
already had one re-cover installed on your original roof system, check with a professional
roofing contractor. In many instances, building code requirements allow no more
than one roof system re-cover before a complete replacement is necessary.
Q: My roof leaks. Do I need to have it replaced completely?
A: Not necessarily. Leaks can result from flashings that have come loose
or a section of the roof system being damaged. A complete roof system failure, however,
generally is irreversible and a result of improper installation or choice of materials
or the roof system installation is inappropriate for the home or building.
Q: Can I do the work myself?
A: Most work should not be done yourself. Professional roofing contractors
are trained to safely and efficiently repair or replace roof systems. You can damage
your roof system by using improper roofing techniques and severely injure yourself
by falling off or through the roof.
Maintenance performed by home and building owners should be confined to inspecting
roof systems during the fall and spring to check for cracked or curling shingles
and cleaning gutters filled with dead leaves and other debris. If you must inspect
your roof system 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 system), if possible.
Q: How long can I expect my roof system to last?
A: Most new roof systems are designed to provide useful service for about
20 years. Some roof system types, such as slate, clay tile and certain metal (e.g.,
copper) systems, can last longer.
Actual roof system life span is determined by a number of factors, including local
climatic and environmental conditions, proper building and roof system design, material
quality and suitability, proper application and adequate roof maintenance.
Roofing product manufacturers offer a variety of warranties on their products. Take
a close look at those warranties to see what responsibilities and financial obligations
manufacturers will assume if their products fail to reach their expected lives.
Q: What will a new roof system cost?
A: The price of a new roof system varies widely, depending on such things
as the materials selected, contractor doing the work, home or building, location
of the home or building, local labor rates and time of year. To get a good idea
of price for your roof system, get three or four proposals from reputable contractors
in your area. Keep in mind that price 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.
There also 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 needs.
Within the roofing profession, there are different levels of expertise and craftsmanship.
Insist on a contractor who is committed to quality work.
Q: How can I determine my annual roofing cost?
A: When considering your roofing options, the following formula may help:
Total Cost (Materials and Labor) ÷ Life Expectancy of Roof System (in years) = Annual
Roofing Cost
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.