Selecting the Right Material
What most homeowners desire is a roof that's not too expensive, requires little maintenance, and lasts forever. But most roofs are replaced - or at least repaired - every ten years. By carefully choosing your home's roofing material, you can reduce the cost of replacement. In the long run, you'll use less building material, fill up less landfill space with discarded material, and put less demand on our natural resources.
You can realize energy saving benefits from your roofing choices. If you select a light-colored surface or a material that doesn't absorb heat from the sun, you significantly reduce your home's cooling needs. When your attic stays cooler, your cooling bills go down.
There is a wide choice of materials used to roof a house, ranging from composition shingles, to slate - pieces of stone. Modern products like plastic, fiberglass and concrete are available, and some innovative, energy-efficient homes are being roofed with sod. New products are being developed to overcome the shortcomings of older roofing materials, meet the demands of modern building techniques, and conform to increasingly stringent building codes.
Popular Roofing Materials
Here is a rundown on the most popular types of roofing. Remember that cost alone does not determine quality, and not all of these products will meet the needs of your home. But by carefully selecting the right material, making sure it's installed properly and performing modest maintenance occasionally, you can have a roof that functions properly for 20 to 50 years - or even longer.
- Metal roofs are coming back into vogue. In the late 1700s, zinc, copper, and lead were the most popular materials used for roofing - such famous historic buildings as the Washington Monument and Thomas Jefferson's Monticello have metal roofs.
Standing-seam steel roofing is the most popular residential metal roofing today. (The term standing-seam describes the upturned edge of one metal panel that connects it to adjacent sections, creating distinctive vertical lines and a trendy historical look.) But metal roofs can also be made to resemble wood shakes, clay tiles, shingles, and Victorian metal tiles. Aluminum or coated steel is formed into individual shingles or tiles, or into modular panels four feet long that mimic a row of shingles or tiles.
Metal roofs are durable, fire retardant and almost maintenance-free. They are also energy efficient; metal reflects heat and blocks its transfer into the attic. Research by the Texas Solar Energy Center in 1985 showed that metal absorbed 34 percent less heat than asphalt shingles, and homeowners switching to metal roofing reported saving up to 20 percent on their energy bills.
Steel roofs offer other environmental benefits as well. They are made from between 60 percent to 65 percent recyclable material. Because they weigh very little, metal roofing can be installed over existing roofs, eliminating the need to dispose of excess material in a landfill.
Installing some metal roofing can be an intricate process best done by a professional, and the initial cost of a premium metal roof is higher than most other roofing materials. You need to compute the lifecycle cost to see if paying more to begin with for a metal roof will prove to be a better investment than some other form of roofing.
Mostly seen in commercial applications, hot mopped asphalt roofing is sometimes applied to flat or semi-flat residential roofs that have good access and proper drainage. Asphalt's advantage is that it is less expensive than other roofing materials and holds up fairly well when properly applied. The technique results in a roof that's not very pretty, although in residential use it is often covered with a layer of decorative stone to improve the appearance.
You've no doubt noticed roofing projects that use this technique, since it requires a large kettle of melted asphalt. When being applied, the hot mixture releases extremely high levels of smelly air pollutants. In addition to being unpleasant, the hot asphalt poses a health risk to installers. Because its fumes contribute to smog, hot mopped asphalt may be restricted in some urban areas.
- Composition shingles are a good choice for a clean look at an affordable price. Higher-quality versions made from asphalt or fiberglass shingles offer a more durable option and may be available with recycled content.
Composition shingles come in a large selection of types, brands and colors. Versatile, they adapt easily to different applications. They are relatively easy to install, and in some applications can be nailed in place over an existing roof. They require low maintenance and can be walked on without damaging the material. Most brands offer Class A fire protection.
On the negative side, composition shingles don't have the life span of other materials like tile or metal. They don't offer the dimensional look of tile or wood shakes, and they can blow off in high winds.
- Wood shakes offer a natural look with a lot of character. Because of variations like color, width, thickness, or cut of the wood, no two shake roofs will ever be the same.
Wood offers some energy benefits, too: it helps to insulate the attic, and it allows the house to breathe, circulating air through the small openings under the felt rows on which wooden shingles are laid.
A wood shake roof, however demands proper maintenance and repair, or it will not last as long as other products. Mold, rot, and insects can be a problem. The life-cycle cost of a shake roof may be high, and old shakes can't be recycled.
Most wood shakes are unrated by fire safety codes. Many use wipe or spray-on fire retardants which offer less protection and are only effective for a few years. There are pressure-treated shakes, however, that are impregnated with fire retardant and meet fire safety standards. This pressure treating extends the life of wood shingles and provides better fire safety performance.
Installing wood shakes is more complicated than roofing with composite shingles, and the quality of finished roof depends on the experience of the contractor as well as the caliber of the shakes you use. The best shakes come from the heartwood of large old cedar trees, difficult to find any more. Some contractors maintain that shakes made from the outer wood of smaller cedars - the usual source today - are less uniform, more subject to twisting and warping, and don't last as long.
- Roofing tile is a good choice for homes with a southwestern, Italian, or Spanish Mission design, or even for homes with a modern, clean look.
Tile lasts a long time - its expected lifespan is greater than the lifespan of the material on which the roofing rests. Tile won't rot or burn, and it can't be harmed by insects. It requires little maintenance, and comes in a variety of colors, types, styles and brands.
The biggest drawback to tile is its weight. Depending on the material used to make it, tile can be very heavy - so heavy that extra roof support can be required. Originally made from clay, new tiles are being made from lighter materials, and lightweight metal tiles can be installed over existing roofs. With some new materials, however, color is added only on the surface of the tile, and they can fade over time.
Some types of tile are fragile, so walking on them can break them. That makes it more difficult to accomplish maintenance like painting or cleaning rain gutters or fireplaces. Initial installation can be complicated.
Finally, tile can cost more than other roofing materials.
- Slate actual shingle-like slivers of rock - is another roofing material that shows up on more upscale homes. Although slate is an expensive choice, it offers a very natural look and can be laid out in a variety of patterns.
The benefits of slate are identical to those of tile: a very long lifespan, good fire protection, low maintenance, and an invulnerably to rot and insects. It comes in a good selection of sizes and colors, although colors are limited to those found in nature.
Like tile, slate can be very heavy, sometimes requiring expensive extra support. It, too, is breakable enough that walking on it is difficult for a non-professional, complicating such tasks as rooftop maintenance, gutter cleaning and painting.
Attic ventilation might seem like a minor consideration, but when properly installed, it can extend the life of your attic and roof structure - saving you hundreds of dollars in repair costs.
During warmer months, ventilation helps keep attics cool. It helps prevent hot, moist summer air from warping the roof sheathing. It also stops shingles from deteriorating prematurely. What's more, fresh air in the attic makes a home much easier to cool, which can result in lower energy costs.
In winter months, ventilation helps reduce moisture to keep attics dry. It stops water from backing up under shingles, damaging insulation, and rotting the roof structure itself. It also helps prevent ice dams from forming. Ice dams occur in areas where snowfall and cold temperatures are common and pose a special problem because they prevent melt water from running off the roof. They can even cause leaks inside your home, resulting in drywall damage.
What is attic ventilation?
Intake and Exhaust
"Ventilate" comes from the Latin word for "to fan." Simply put, it's the action of moving air. Out with the hot. In with the cool. And that's exactly how ventilation works. It provides conditions that allow air to flow. Every time stale, overheated air in your home or attic is vented out and fresh air is pulled in to replace it, you have what is known as an "air exchange." But ventilation is much more than a simple breeze blowing through your house. It's a process that provides a steady, high volume of air movement. Think about it as a system of components, all sized and positioned to provide constant intake and exhaust of air.
According to most building codes, you need one square foot of vent area for each 150 square feet of attic floor space. The minimum is one square foot for every 300 square feet of attic floor space if there is a vapor retarder or the space is balanced between the ridge and intake vents. A balanced ventilation system means about 50 percent of the required ventilating area should be provided by exhaust vents in the upper portion of your attic with the remaining 50 percent provided by intake vents.
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:
- Roof covering: shingles, tile, slate or metal and underlayment 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.
Organic shingles consist of a cellulose-fiber (i.e., wood) base that is saturated with asphalt and coated with colored mineral granules.
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.
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. 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.
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.
© National Roofing Contractors Association
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