Roof Systems FAQ
COOL ROOFING SYSTEMS:
What is a cool roof?
Cool roofs, also called white roofs, are a highly reflective and emissive roof coatings that stays 50 to 60 degrees F cooler in the summer sun, thereby reducing energy costs, improving occupant comfort, cutting maintenance costs, increasing the life cycle of the roof, and contributing to the reduction of urban heat islands and associated smog.
What kinds of roofing products are available for residential applications?
There are several. Check out our articles about the different types of roofing systems available by clicking here
How cool is a cool roof?
During the summer, a typical dark roof is 150 to 190 degrees Fahrenheit at peak, while cool roofs peak at 100 to 120 degrees Fahrenheit.
SLATE ROOF SYSTEMS:
How much does a slate roof cost?
A simple, straightforward slate roof starts out at $12 per square foot and can run more than $20 per square foot depending on the type of slate used, the design of the roof, the height of the building, the pitch of the roof, and so forth. Most slate roofs run between $12 and more than $20 per square foot, installed.
Besides the low life cycle cost, why else should one install a slate roof?
Aesthetics: Slate roofs come in a wide variety of sizes, colors, and thicknesses. One can create many different looks to enhance just about any architectural style. Click here for GAF/ELK’s virtual design studio to get a visual perspective on styles and colors of slate roofing.
Ecological considerations: Slate is a natural product that comes out of the ground and can safely go back into the ground. Petrochemical roofing made of asphalt and fiberglass typically lasts twenty years. According to statistics, construction and demolition debris make up 28% (by weight and volume) of the refuse being placed in landfills. That is more than the waste from Styrofoam, fast-food packaging, disposable diapers, and all plastic packaging combined! Approximately 20% of all construction debris is roofing. Though not the only reason, environmental concern is certainly a good reason for installing slate.
Effective protection: A slate roof is the best chance you have for getting a leak-free roof. Most leaks in roofs occur in flat areas and areas with protrusions. Since slate roofs are installed by craftsmen who are thinking in service life of decades or even centuries, these details are usually installed with great care. As a result, the quality of leak protection is much higher. Thus slate roofs leak much less often than other kinds of roofing — especially on houses with complicated roof lines. Slate roofs are much more wind resistant than asphalt roofs. Slate roofs also do not rely on the underlying roofing felt to remain leak proof the way many clay and concrete tile roofs do.
Long-term Reliability: Slate has been the material of choice for a large percentage of the most important buildings built in the last five centuries. The method of installation has changed little over five centuries. New roofing products, such as many of the simulated slates, have come and gone in less time than asphalt roofs last. Some of these products have been sold with 50-year warranties, which became worthless when the businesses went under.
Is a slate roof fireproof?
Slate itself is fireproof. A slate roof is one of the most fire resistant roofs that exist. However, the wood deck under the slate is not fireproof. Often fires will jump from house to house as sparks hit adjacent roofs, igniting the surface if it is a flammable material. Many of the raging fires that engulf hundreds of houses every year would not occur if the houses were covered in slate.
Does a slate roof need to be cleaned periodically?
No. Slate requires no cleaning
Does a slate roof need periodic maintenance?
Yes. Even new slate roofs will shed a few slates from time to time. It is a good idea to visually inspect a slate roof at least once a year. The owner of the property can do this annual inspection. Any slates that are seen to be missing, sliding, or broken should be replaced every few years. It is always a good idea to have a more careful inspection from a slate roof expert.
Are there any special framing or structure considerations for slate?
A good solid deck with 16” on center framing is preferred. Most structures are built to handle wind and snow loads that far exceed the weight of slate. However, a weak structure that has too much flex to it will result in a poorly installed slate roof. Ideally, one would use a 3⁄4” thick tongue and groove deck on 2” x 12” rafters 16” on center. However, this is an expensive deck, and would be a rare sight today. Otherwise, it would be best to have at least 5/8” plywood or 3⁄4” plywood over 16” on center trusses built to handle slate.
METAL ROOFING SYSTEMS:
Why should I spend a little more for a metal roof?
Ordinary roofing materials have shorter life spans than metal and will need to be replaced regularly. With constantly increasing material and labor costs, that could mean a significant expense over the life of your building. A metal roof virtually never needs to be replaced, saving you money while adding value to your residential or commercial structure.
How much protection does a metal roof offer?
FIRE: A metal roof will not burn or support combustion.
WIND: Experience at recent hurricanes has shown that metal roofs outperformed other roofing products.
WATER: A metal roof has a low rate of water absorption, greatly reducing damage to structure. And a metal roof cannot be penetrated by hail.
How can a metal roof save money on energy bills?
Metal reflects the majority of the sun’s rays, so it doesn’t retain as much heat as wood, asphalt shingles, tile or cement. This means a metal roof could help your attic stay cooler longer - leading to a significant reduction in your building’s energy bills.
Is a metal roof noisy when it rains?
Contrary to popular belief, metal roofs are not noisy when it rains. In fact, according to one study, metal roof’s noise levels are about the same as other products like asphalt shingles, wood shingles or clay tiles.
Can I walk on my metal roof?
Yes, but since a metal roof requires virtually no maintenance, there should be no reason to do so. Like any roof, care should be exercised. You can discuss specific details about walking on your metal roof with your installation company.
Does my present roof have to be removed before a metal roof is installed?
In most applications over asphalt, our metal roofs can be applied directly over the old roof, saving money and eliminating a great deal of mess. In addition, because there is no old roof to dispose of, landfill space is spared, helping to protect our environment.
How much do these metal roofs weigh in comparison to other types of roofing?
Metal roofing materials are less than one-third the weight of asphalt, one-twentieth the weight of concrete, and add less than 10% to the weight of the existing roof materials.
Does the roof need to be grounded?
Grounding of any exterior metal siding or roofing is not recognized as necessary by any major building code organization. Occasionally, certain municipalities or local building codes may require it. Detailed grounding instructions are available. Because metal roofing is both an electrical conductor, and a noncombustible material, the risks associated with its use and behavior during a lightning event make it the most desirable construction material available.
How long will a metal roof last?
A metal roof won’t dry out, split, curl, peel or flake like conventional roofing products. Metal roofing has been successfully used for centuries and they last substantially longer than any other roofing product on the market.
CLAY AND TILE ROOFING SYSTEMS:
How long do tile roofs really last?
No one knows for sure. Tile roofs date back to Neolithic China, and many
Ancient structures with tile roofs still exist. In Europe and Asia roof tiles have
been the primary roofing product for hundreds of years. Both clay and concrete
Tile roofing systems, when installed properly, will withstand weather conditions
that begin to deteriorate other roofing products the day they are installed. In
general, a tile-roof, clay or concrete - may outlast the building it protects.
Are roof tiles available in shapes other that Spanish
or Mediterranean?
Yes. Roof tiles come in many colors, shapes and sizes. In fact, with
modern innovations, clay and concrete roof tile manufacturers produce tiles
that suits any architectural style, from authentic Spanish and Mediterranean to
New England Colonial, historic or contemporary. Roof tiles can be flat or
round, simulate wood shakes, or slate replicate centuries-old roofing materials.
The possibilities are virtually limitless.
Why consider a tile roof instead of asphalt shingles?
VALUE: Resale and property values…
APPEARANCE: There is not an asphalt shingle on the market that can match
the superior aesthetics of clay and concrete roof tile. The numerous styles,
hundreds of colors, and variety of finishes available with roof tile allow you
and your designer to create a roof to suit nearly any architectural style or one
that is entirely unique.
PERFORMANCE: Roof tile has been used for centuries worldwide and for
good reason. Both clay roof tile and its modern partner, concrete, are not
only beautiful but also extremely durable. With proper building design and
installation, tile roofs can last 50 to 100 years or more. They do not rot in wet
climates and are not susceptible to destruction by pests. Tile roofs can be
used in any climate or region and can withstand fire, earthquakes, the sever-
est weather conditions, including hail, wind and snow. For these reasons,
most roof tile manufacturers offer product warranties of at least 50 years.
ENVIRONMENTALLY FRIENDLY: Both clay and concrete roof tiles are made
from naturally occurring materials that do not deplete precious natural
resources. They are manufactured without chemical preservatives. And old
tiles can be recycled to make new tiles or other products.
COST EFFECTIVE: With superior aesthetics, durability and longevity, roof tile
is a cost-effective alternative to other roofing products. A simple comparison
of life cycle costs makes it clear that a tile roof is one of the best available today.
“I saw a news picture of a home with a tile roof surrounded by
homes burned to the ground.
Do tile roofs protect my home from fire better than other roofing materials?
Clay and concrete tiles are completely non-combustible. The complete roof
assembly has a Class “A” fire rating, the highest fire resistant rating available.
Buildings with Class “A” rated tile roof systems should be eligible for the
lowest fire insurance rates.
What about the insulation value of a tile roof?
Tile roofs are good insulators. The combined effect of the roof tiles, air space, and decking allows for better air circulation and reducing direct heat transfer. This should lower energy costs year round. Aesthetically pleasing, more durable than other roofing materials, and able to withstand extreme weather conditions, tile has been the first roofing choice in Europe and Asia for centuries. Tile’s durability has been clearly demonstrated by how well it has withstood the test of time, weather and natural disasters. Tile perfectly complements the architectural styling of any home or building. There is tile that duplicates wood shake; just right for that ranch-style home. There’s tile that replicates slate; a fitting choice for the Tudor style and of course the rounded tiles are ideal for Spanish and Mediterranean structures. The lifecycle cost of tile (annual cost over its expected life)is much less than metal, treated wood shakes, asphalt, or fiberglass shingle
roofs. This makes tile a natural choice; not just for durability, but also for its long-term economical benefits. To ensure that tile roofing continues the traditions of excellence, the Tile Roofing Institute member companies are constantly testing their products in extreme, real-world conditions. Striving for continuous improvement, the Tile Roofing Institute member companies have demonstrated that buildings with tile roofs provide the greatest protection and best value of any roofing material. Every year, regardless of the part of the country, wild fires devastate hundreds of homes.
In independent testing, concrete and clay tile roofing has proved to be safer than traditional
roofing materials such as shingles, wood shake or metal. By design, a tile roof is allowing air circulation under the tile, which reduces heat transfer to the attic during a fire. For homeowners living in an area prone to tornadoes, hurricanes or extreme winds, roof tile provides one of the best defenses against weather-related property damage. One of the best attributes of concrete and clay tile roofing is its resistance to severe storms and hurricane-force winds. Its design and construction provide high air permeability, which helps relieve wind stress. Independent testing sponsored by the Tile Roofing Institute has shown that with proper attachment, clay and concrete roof tiles can sustain winds in excess of 125 miles-per hour that would have stripped off most other roofing materials. Different parts of the country are susceptible to devastation from extreme hailstorms. Clay and concrete roof tiles can resist damage from hailstones as large as 1.5”, just larger than a golf ball. A tile roof system provides two layers of protection from the elements. The tile itself provides a tough water-shedding outer shell. An underlayment of asphalt roofing paper over the roof decking provides the inner shell if the tile was struck by extremely large hailstones. This is real protection that few other roofing systems can provide. Independent testing at the University of Southern California has shown that clay and concrete tile roofing systems, when installed according to building code standards, exceed current seismic load requirements for building materials.
STEEP SLOPE ROOFING:
How many homes are topped with asphalt shingles? Why?
Asphalt shingles are the leading choice for residential roofing in the United States because they provide quality, durability, versatility and economy. Over 12.5 billion square feet of asphalt shingle products are manufactured annually – enough to cover more than 5 million homes every year. Four out of five homes are roofed with asphalt shingles.
Asphalt shingles offer consumers the broadest array of colors, shapes, and textures available. With an enormous range of styles, asphalt shingles can match almost every type of architectural design and achieve virtually any desired effect – and do it affordably.
What are some of the benefits of asphalt shingles?
PRODUCT PERFORMANCE. Asphalt shingles perform well in extreme temperatures and in areas where wind, water, and ice are prevalent.
AFFORDABILITY. The efficient, high-volume production and relatively low application cost of asphalt shingles provide consumers with an overall value that’s tough for other roofing materials to match, especially in terms of comparable life expectancy.
LOW MAINTENANCE. Asphalt shingles, when properly chosen and applied, require little or no regular upkeep, and are easily repaired if damaged.
EASE OF APPLICATION. Asphalt shingles are considered to be the easiest of all standard roofing materials to apply. In addition, the flexibility and strength of asphalt shingles supports their application on a wide variety of roof designs.
FIRE AND WIND RESISTANCE. Asphalt shingles are manufactured to resist external fire and flammability standards, and carry Class A, B or C fire ratings, with Class A providing the greatest fire resistance. These fire ratings are defined by nationally recognized standards and tested by independent testing agencies. In addition, many asphalt shingles carrying a “wind resistance” label indicate that they have been manufactured and tested to demonstrate acceptable resistance in high-wind locations.
How are asphalt shingles made?
In the United States, asphalt shingles are categorized as either organic-based or fiberglass-based.
Organic-based asphalt shingles are manufactured with a base (also termed mat or substrate) made of various cellulose fibers, such as recycled waste paper and wood fibers. This organic base is then saturated with a specially formulated asphalt coating and surfaced with weather resistant mineral granules.
Fiberglass-based asphalt shingles are manufactured with mat composed entirely of glass fibers of varying lengths and orientations. This fiberglass base is then surfaced with a specially formulated asphalt coating, followed by weather-resistant mineral granules.
What are the different types of asphalt shingles and which one is right for my roof?
The two basic types are composition and fiberglass-based shingles.
Composition shingles are made of organic felt manufactured from wood and paper fibers.
Fiberglass base shingles are made of man-made fiberglass mat.
Both kinds are soaked in asphalt, but the fiberglass base shingles are more fire-resistant than the organic ones. Although asphalt shingles may look like individual tabs, they are generally manufactured in 12 inch by 36 inch pieces that are notched to look like smaller units. The exposed portion is called “exposure” and the lower edge is referred to as the “butt.” They come in a variety of weights. Generally speaking, the heavier the shingles, the longer they last. Choosing from the wide assortment of available colors, textures, patterns and weights can be daunting. Most homeowners prefer premium-weight shingles, which may weight 430 pounds per square, compared with standard shingles at about 230 pounds. Because these are more three-dimensional, they do a better job of mimicking the texture of real wood shingles.
Strip Shingles: these asphalt shingles are approximately three times as long as they are wide. Manufactured in both standard and metric dimensions, strip shingles are distinguished by the number of cutouts or tabs that they have. The most common type of strip shingle is the “three-tab” shingle. Different textural and lighting/shadowing effects can be achieved with strip shingles depending on the number, shape and alignment of the cutouts.
Laminated Shingles: these special shingles contain more than one layer of tabs to create extra thickness. They are also referred to as three-dimensional or architectural shingles because they create visual depth on a roof and impart a custom look. Laminated shingles continue to be a favorite among builders, roofing contractors and home buyers.
Interlocking Shingles: as the name suggests, interlocking asphalt shingles are individual shingles that mechanically fasten to each other, and are used to provide greater wind resistance. They come in various shapes and sizes providing a wide range of design possibilities.
Large Format Shingles: generally rectangular or hexagonal in shape, these shingles do not utilize cutouts or tabs.
How do I determine if my asphalt shingle roof should be replaced?
Sooner or later, every roof needs to be replaced, usually due to the long-term effects of weathering. If a residential roof is more than 20 years old, it is a prime candidate for re-roofing.
To determine if you need a new roof:
On the ground, walk around your home with binoculars and inspect your roof for cracked, curled or missing shingles, as well as any excessive loss of the protective mineral granules. DO NOT CLIMB ON THE ROOF; walking on the roof is dangerous and can damage your roof.
In your attic, take a flashlight and look at the underside of the roof deck and rafters for any stains or wet spots indicating water leaks.
Asphalt shingles can often be applied directly over existing roofs without the necessity of tearing off the old roof. However, new shingles cannot be properly applied over hard or brittle materials, uneven surfaces for nailing or roof decks with warped, rotted or unsound support that should first be replaced or repaired.
Some local ordinances forbid re-roofing over two or more layers of shingles. If a home already has been shingled several times, it is important to first determine if the roof deck can support another layer of shingles before undertaking any re-roofing project.
What is roll roofing?
In addition to asphalt shingles, asphalt roll products are used for residential roofing applications (primarily for underlayments and flashings). There are four basic types of roll roofing materials, each tailored for use in certain job requirements:
Smooth Surfaced Roll Roofing: Also termed coated felt, this smooth-surfaced roll roofing is covered with ground talc or mica. It is used primarily as flashing to seal the roof at intersections and protrusions, and for providing extra deck protection at the roof’s eaves and valleys.
Saturated Felt: This asphalt-impregnated, organic-based felt is used as an underlayment between the roof deck and the roofing material. Saturated felt is produced in a variety of weights.
Specialty-Eaves Flashings: This self-adhering, polymer-modified bituminous sheet material is designed for special flashing applications along roof eaves and in other areas. It is used particularly in regions where ice dams and water backups are common.
Mineral-Surfaced Roll Roofing: This type of roll roofing is used alone as a primary roof covering, most frequently on small or secondary-use buildings such as supply buildings, barns, garden sheds, etc. The top surface of the roll is imbedded with mineral granules.
How much do asphalt shingles cost?
Depending upon weight and quality, asphalt shingles can cost anywhere from about $90 to $175 per square installed (a square refers to a roof area equal to 100 square feet).
What are some Steep Slope roofing terms?
Architectural Shingles: (See Laminated Shingles below)
Asphalt: A bituminous waterproofing agent applied to roofing materials during manufacture.
Deck: The structural surface to which the roofing or waterproofing system (including insulation) is applied.
Flashing: Pieces of metal or roll roofing used to prevent seepage of water into a building around any intersection or projection in a roof, such as vent pipes, chimneys, adjoining walls, dormers and valleys.
Granules: Ceramic-coated colored crushed rock that is applied to the exposed surface of asphalt roofing products.
Hip: The inclined external angle formed by the intersection of two sloping roof planes. Runs from the ridge to the eaves.
Incline: The slope of a roof expressed either in percent or in the number of vertical units of rise per horizontal unit of run. Also referred to as slope.
Interlocking Shingles: Individual shingles that fasten together mechanically and provide greater wind resistance.
Laminated Shingles: These shingles have more than one layer of tabs to create extra thickness. They are often referred to as three-dimensional or architectural shingles because they create visual depth on a roof and impart a custom look.
Large Format Shingles: Generally rectangular or hexagonal in shape, these shingles do not have cutouts or tabs.
Membrane: A roof covering or waterproofing layer whose primary function is the exclusion of water.
Re-covering: The process of covering an existing roofing system with a new roofing system.
Re-roofing: The practice of removing an existing roofing system and replacing it with a new roofing system.
Ridge: The uppermost, horizontal external angle formed by the intersection of two sloping roof planes.
Roll Roofing: Asphalt roofing products manufactured in roll form, either smooth- or mineral-surfaced.
Saturated Felt: An asphalt-impregnated felt used as an underlayment between the deck and the roofing material.
Self-Adhered Eave and Flashing Membrane: A self-adhering waterproofing shingle underlayment designed to protect against water infiltration due to ice dams or wind driven rain.
Strip Shingles: Manufactured in both standard and metric dimensions, these asphalt shingles are approximately three times as long as they are wide, and are distinguished by the number of cutouts or tabs that they have. The most common are three tab.
Square: A unit of roof measure covering 100 square feet.
Thermal Insulation: A material applied to reduce the flow of heat.
Three-Dimensional Shingles: (See Laminated Shingles above)
Underlayment: Asphalt saturated felt used beneath roofing to provide additional protection for the deck.
Valley: The internal angle formed by the intersection of two sloping roof planes.
Vapor Retarder: A material designed to impede the passage of water vapor into the roofing system.
LOW-SLOPE ROOFING
What are the major low-slope roofing systems?
The two broad categories of asphalt roofing systems for commercial, industrial and institutional buildings are Built-Up Roofing (BUR) and Modified Bitumen Systems (MBS).
What is Built-Up Roofing (BUR)?
Built-up Roofing (BUR) is the most popular choice of roofing used on commercial, industrial and institutional buildings. BUR is used on flat or low-sloped roofs and consists of multiple layers of bitumen and ply sheets. Components of a BUR system include the roof deck, a vapor retarder, insulation, membrane and surfacing material. The components are assembled at the job site to actually form the built-up roof. At the heart of this roofing system is the roofing membrane, which consists of roofing bitumen and multiple reinforcing plies of roofing felt. Roofing bitumen is the primary adhesion/waterproofing agent used between roofing plies. Bitumen arrives at the job site in solid form, but is heated and applied as a liquid. Roofing bitumens may be either a product of petroleum refining (asphalts) or a product of the coal-cooking process (coal tar pitch).
Multiple reinforcing “plies” are asphalt-coated roofing sheets or felts installed in three or more layers to strengthen and stabilize the BUR membrane. These multiple reinforcing felts also make the membrane more pliable and resilient, protect the bitumen from water degradation, and serve as a fire-retarding element in the membrane system.
BUR roofing membranes can be protected from solar radiation by embedding gravel in the bitumen, applying a surface coating or applying a granular-surfaced “cap” sheet. Light-colored surfacing materials can be used to reflect heat from the building. In addition, surfacing agents can provide additional fire protection.
How is BUR applied for maximum performance?
It’s critical to get secure bonding of the roofing felts (plies) using bitumen. To achieve this bond the roofing contractor applies thin, uniform moppings of bitumen. This waterproofs the system and ensures proper adhesion for fusing the membrane system together. The temperature of the bitumen is critical. By heating it to the proper temperature the roofing contractor gets the right viscosity for proper mopping. The contractor heats the bitumen to its EVT or Equiviscous Temperature, the temperature at which it can be most effectively mopped into uniform layers. Each batch of bitumen should be labeled by the supplier with its EVT. Once felts are rolled into place on the heated bitumen applicators pull brooms or squeegees over the felt or use some other method to make sure that its embedded in the bitumen. The strength of the membrane depends on the type of felt used, the number of plies, overall ply construction, and the lapping of the overlaying felts. Typically, membrane ply construction is defined by headlap, endlap, and sidelap.
Headlap is the distance of the overlap that exists between the lowermost and the uppermost plies of the shingled portion of the roof membrane when measured perpendicular to the long dimension of the membrane.
Endlap is the overlap distance that is measured from where one roll of felt ends to where another begins.
Sidelap is the overlap distance along the length of the felt where one roll of felt overlaps the adjacent overlying felt.
The application of Built-Up Roofing systems is detailed work, but the professional who pays particular attention to those details such as curbs, walls, flashings or other projections that interrupt the membrane, achieves a quality, efficient, long-lasting product for the building owner.
What are some of the advantages of BUR?
Built-up roofing systems (BUR) have had a long-standing popularity, due in large part to the success and proven reliability of BUR. The stock of 20, 30 and 40-year-old BUR roofs still in excellent condition attests to this fact.
Specifically, BUR roofs offer:
Multi-Layer Protection – the multiple layers of bitumen and bitumen saturated “felts” make a watertight barrier capable of providing many years of reliable protection from the elements.
Thermal Performance – Built-up roofing systems exhibit exceptional resistance to the conduction of heat between the exterior and interior of a building, resulting in noticeable reductions in heating and cooling costs.
Fire and Uplift Resistance - Built-up roofing systems are tested through Factory Mutual Research Corporation to meet very strict fire resistance requirements and ensure adequate uplift resistance under extreme wind conditions.
Economy - Compared to other high performance commercial roofing systems, built-up roofing is one of the best investments on the market due to its competitive cost per year of expected service life.
What is Modified Bitumen (MB) or Modified Bitumen Membranes (MBS)?
Modified bitumen membranes (MBS) combine the features of a built-up roof with the added tensile strength from its polymer modification. Using a reinforced sheet that is prefabricated in the plant, modified bitumen systems require a less labor-intensive application and can be applied cross-platform in both commercial and certain residential applications.
A modified bitumen roofing system is composed primarily of polymer-modified bitumen reinforced with one or more plies of fabric such as polyester, fiberglass or a combination of both. Factory surfacing, if applied, includes mineral granules, slag, aluminum or copper. The bitumen determines the membrane’s physical characteristics and provides primary waterproofing protection; while the reinforcement adds strength, puncture resistance and overall system integrity.
Factory-assembled, modified bitumen membranes undergo strict quality control standards to ensure uniform thickness and consistent physical properties throughout the membrane. The finished roofing system is usually a two- to four-ply system consisting of a modified bitumen membrane and a base sheet, with additional plies for added strength if needed. The substrate often determines which ply system is best specified.
The finished roofing membrane may consist of one or more modified bitumen sheets, or it may be comprised of a combination of built-up roofing (BUR) felts and one or more modified bitumen sheets. The type of substrate and the performance objectives influence the specification of the modified bitumen membrane system.
There are modified bitumen membranes tailored to almost every type of construction design and climate: for new roofing or re-roofing of commercial buildings, residential high rises, domes, spires, and most categories of low-slope or steep-roof roofing. Thus there are a variety of modifiers, and types of reinforcements and surfacings available.
What are Modified Bitumen modifiers? How do they work?
Modified bitumens generally use a traditional waterproofing medium — asphalt — modified with atactic polypropylene (APP), styrene butadiene styrene (SBS), synthetic rubber or other agents that create a uniform matrix that enhances the physical properties of the asphalt. SBS and APP are the most common bitumen modifiers.
SBS (Styrene-Butadiene-Styrene) modifies the asphalt by forming a polymer network within the bitumen. SBS gives the bitumen rubber-like characteristics and improved resistance to aging and weathering. Most SBS-modified bitumen sheets are either set in hot mopping asphalt, torch-applied or adhered with cold-process adhesives. SBS-modified bitumen sheets that do not have factory applied granule or foil surfacing need some form of field-applied ultraviolet protective coating.
APP (Atactic Polypropylene) is a thermoplastic polymer, which forms a uniform matrix within the asphalt. This enhances the bitumen’s performance by increasing its UV resistance, increasing its flexibility at low temperatures and improving its flow resistance at high temperatures. APP-modified bitumen sheets are generally applied using a propane-fueled torch. Applicators use the heat to soften the modified bitumen on the underside of the sheet. The sheet’s bottom surface becomes a molten adhesive, which flows upon the substrate and then cools to form a waterproof adhesive bond. Some APP sheets can also be applied with cold process adhesives.
What are reinforcing plies? What are they made of?
While modified asphalt provides the primary waterproofing characteristics of these membranes a reinforcing ply adds strength and puncture resistance. Glass fiber and polyester plies are the most commonly used reinforcing fabrics. Each has distinctive properties. Polyester has excellent elongation, tensile strength and recovery. It provides good puncture resistance and stands up well to foot traffic. Glass fiber resists flame penetration and provides excellent tensile strength and dimensional stability.
How do I choose the roofing system that works best for a particular job?
The combination of asphalt, modifiers and reinforcements determines the characteristics of a specific modified bitumen membrane. To obtain the best roofing system possible, the designer, building owner and contractor should understand the dynamics of the roof as well as the roofing system when specifying either APP or SBS modified roofs.
The architect, specifier, building owner, and roofing contractor should examine the following parameters when choosing a roofing system:
- What is the building’s type and usage?
- What building code requirements apply to the system?
- What is the estimated service life of the roof system?
- What kind of roof deck will be used (type, size, slope)?
- How much is the roof deck expected to move relative to the roof perimeter?
- Shrinkage of the deck material?
- Moisture content of the deck?
- Access for equipment on the roof?
How is Modified Bitumen roofing applied for maximum performance?
The application of modified bituminous roofing is a construction process that involves the skillful arrangement of several components as specified for the process. Roof performance is determined by factors that include building design, job specifications, materials quality and suitability, application procedures and maintenance. The level of quality in the workmanship during the application process is critical.
The application of modified bitumen roof systems is not an exact science. It’s a craft that involves people, roofing professionals, who deal with a broad range of materials, designs, customs, techniques, weather events, and climates.
Why choose Modified Bitumen roofing systems?
Click here to see the Asphalt Roofing vs. Competition Chart
Since gaining acceptance in the roofing industry during the 1970s, the use of modified bitumen membrane roofing systems has increased steadily. Today modified bitumen membranes are the fastest growing roofing materials in the industry. Considered a quality “hybrid” system, MBS provides the features of a built-up roof with the added tensile strength and elongation of a modified bitumen cap sheet, as well as the quality assurance of in plant membrane fabrication uniformity and control, and reduced labor requirements for installation. In addition, MBS products undergo the same fire and uplift resistance testing standards as BUR, providing the commercial customer full assurance of appropriate fire and uplift resistance.
What are some low-slope roofing terms?
APP (Atactic Polypropylene): A modifier of asphalt (see modified bitumen roof membrane) that increases the UV resistance of the bitumen as well as its flexibility at low temperatures and improves its flow resistance at high temperatures.
Asphalt: A bituminous waterproofing agent applied to roofing materials during manufacture.
Built-Up Roof (BUR): A flat or low-sloped roof consisting of multiple layers of asphalt and ply sheets.
Base Sheet: A saturated or coated felt installed as the first ply in some multi-ply modified bitumen roofing assemblies.
Bitumen: (1) a class of amorphous, black or dark colored (solid, semi-solid or viscous) cementitious substances, natural or manufactured, composed principally of high molecular weight hydrocarbons and found in asphalts, tars, pitches and asphaltines; (2) a generic term used to denote any material composed principally of bitumen.
Bituminous: Containing or treated with bitumen.
Cap Sheet: A granule-surfaced coated sheet used as the top ply of a modified bitumen roof membrane.
Coated Sheet or Felt: (1) an asphalt felt that has been coated on both sides with harder, more viscous asphalt; (2) a glass fiber felt that has been simultaneously impregnated and coated with asphalt or coal tar on both sides.
Cold-Applied Roofing: A continuous roof membrane, consisting of plies of felts, mats or fabrics that are laminated on a roof with alternate layers of cold-applied roof adhesive and surfaced with a cold-applied coating.
Deck: The structural surface to which the roofing or waterproofing system (including insulation) is applied.
Felt: A flexible sheet manufactured by the interlocking of fibers through a combination of mechanical work, moisture, and heat. Felts are manufactured principally from vegetable fibers (organic felts), glass fibers (glass fiber felts), or polyester fibers (polyester felts); other fibers may be present in each type.
Fiberglass Mat: An asphalt roofing base material manufactured from glass fibers.
Flashing: Pieces of metal or roll roofing used to prevent seepage of water into a building around any intersection or projection in a roof, such as vent pipes, chimneys, adjoining walls, dormers and valleys.
Granules: Ceramic-coated colored crushed rock that is applied to the exposed surface of asphalt roofing products.
Incline: The slope of a roof expressed either in percent or in the number of vertical units of rise per horizontal unit of run. Also referred to as slope.
Low-Fuming Asphalt: An asphalt that contains a small amount of special
Polymer that, when heated, floats to the surface, creating a skim layer on
the asphalt in the kettle that traps most of the fumes.
Membrane: A roof covering or waterproofing layer whose primary function is the exclusion of water.
Modified Bitumen Roof Membrane: A continuous, semi-flexible roof membrane assembly consisting of plies of saturated felts, coated felts, fabrics or mats between which alternate layers of bitumen are applied, either surfaced or unsurfaced.
Organic Felt: An asphalt roofing base material manufactured from cellulose fibers.
Re-covering: The process of covering an existing roofing system with a new roofing system.
Re-roofing: The practice of removing an existing roofing system and replacing it with a new roofing system.
Roll Roofing: Asphalt roofing products manufactured in roll form, either smooth- or mineral-surfaced.
Saturated Felt: An asphalt-impregnated felt used as an underlayment between the deck and the roofing material.
SBS (Styrene-Butadiene-Styrene): A modifier of asphalt (see modified bitumen roof membrane) that enhances the bitumen’s ability to resist the effects of aging the weather.
Self-Adhering Membrane: A membrane that can adhere to a substrate without the use of an additional adhesive. The undersurface of a self-adhering membrane is protected by a release paper or film, which prevents the membrane from bonding to itself during shipping and handling. These membranes can be base sheets, ply sheets, cap sheets or underlayments.
Smooth-Surfaced Roof: A roof membrane surfaced with a layer of hot-mopped asphalt, cold-applied asphalt-clay emulsion, cold-applied asphalt cutbacks, elastomeric coating, or sometimes with an unmopped, inorganic felt.
Square: A unit of roof measure covering 100 square feet.
Thermal Insulation: A material applied to reduce the flow of heat.
Underlayment: Asphalt saturated felt used beneath roofing to provide additional protection for the deck.
Vapor Retarder: A material designed to impede the passage of water vapor into the roofing system.