As a property owner, you might wonder what are the options for a flat roofing system. There are many roofing materials out there, ranging in price, style, and durability. Asphalt shingles or clay tiles may be common on many homes with sloped roofs, but a flat roof system requires its own considerations.
The main difference between a sloped roof and a flat roof comes down to controlling water runoff. A flat or low-slope roof needs a quality seal to protect the underlayment from moisture damage. One time-honored option for your low-slope roof is a built-up roofing system.
Why built-up roofing?
Built-up roofing has been used for over 100 years in the U.S. specifically for low slope roofs. A roof with a low slope may present issues with water runoff, especially if outlets or downspouts become plugged with leaves and debris. Flat roofs tend to collect large amounts of water compared to higher sloped roofs. Though common on many homes, ordinary roof shingles won’t seal out standing water as they are designed to shed water downward rather than creating a watertight surface. The seal created by a built-up roofing system is specifically designed to protect your low slope roof for years to come.
Light-colored gravel can even help reflect the sun, potentially lowering energy costs by lowering the temperature inside the structure. A built-up roofing system can last from 15 to 30 years on average under proper maintenance and depending on environmental factors.
What is built-up roofing?
Also known as BUR, built-up roofing is a roofing material intended for flat or low-slope roofs. BUR is valued over other roofing types because it provides a continuous sealed surface, which is important for repelling water and protecting the roof.
What is built-up roofing made of?
BUR is composed of alternating layers of bitumen (asphalt), tar, coal tar, and reinforcing fabric, and is then finished with an aggregate layer like gravel or stone. Most built-up roofing with gravel, or “tar-and-gravel” roofing, are composed of fiberglass-based asphalt sheeting with hot bitumen (“tar”) mopped on between each layer. The gravel or crushed rock is meant to keep the roofing material in place and to protect it from the elements and abrasion.
Built-up roofing types?
1. Ballasted asphalt built-up
A ballasted roof is not adhered or anchored to the roof membrane in any way. You may wonder how the loose gravel doesn’t blow away, but this is because the stones used in this type of BUR have a bigger diameter. A thick layer is applied with fasteners and plates to secure it.
Installation is fairly easy since the gravel is simply blasted onto the deck. With this process, this roofing system can be installed any time, under any weather condition. The stones naturally form a fireproof layer, which makes this built-up roofing a standout candidate for fire-resistant roofing systems.
2. Cold built-up
A cold built-up roof is a good choice for buildings that must remain occupied during a roofing project, such as hospitals and schools, and on roof areas with limited accessibility. This roofing system is similar to an adhesive, requires no heat, and is applied with a squeegee. The benefits include no toxic fumes during installation, the availability of products containing recycled content, and not being affected by weather during application.
3. Hot built-up
Unlike ballasted or cold BUR, hot built-up roofing involves heat in the installation process. A hot built-up roof uses liquefied bitumen. Due to the heating aspect, this installation process is the most difficult, has a risk of toxic fumes, and has a higher risk of fire. Moreover, hot BUR does not generally perform as well as a cold-applied BUR.
Built-up roofing weight?
The weight of a built-up roofing system can range from about 2.5 pounds per square foot for a smooth surface to 6.5 pounds per square foot for a gravel surface. Though not nearly as heavy as a slate roof or a clay tile roof, built-up roofing is generally heavier than asphalt shingles, TPO, PVC, and metal roofs.
Built-up roofing vs. single ply?
Single-ply membranes are sheets of synthetic materials that can be chemically adhered to insulation or ballasted. There are two main types of single-ply membrane commercial roofing: Thermoplastic Polyolefin (TPO) and Ethylene Propylene Diene Terpolymer (EPDM).
Cost per square foot: EPDM $3.50–$7.50, TPO $3.50–$6.50
Installation: TPO uses a hot-air gun to fuse the membrane at the seams. EPDM is joined together with seam tape
Pros: commonly used in commercial roofs; TPO’s light color makes it highly reflective; less expensive than BUR; lighter in weight than other materials
Cons: less durable than BUR; seams make it susceptible to water damage; potential fire hazard in installation; needs added fire retardant chemicals during the manufacturing process
Built-up roofing systems, commonly referred to as “tar-and-gravel” roofs, give you the choice of how many layers (plies) to install.
Cost per square foot: $5.50–$8.50
Installation: alternating layers of bitumen and reinforced fabric, with a layer of rock
Pros: backed by many years of use; protection from UV rays, extreme heat or cold, and wind damage; seamless layer is highly water resistant; naturally fire resistant; can be installed any time/ in any weather; low maintenance
Cons: adds extra weight to roof; slower installation process; higher installation costs; potential risk of toxic fumes
Built-up roofing advantages and disadvantages?
Built-up roofing is a great option for your flat roof, but as with any roofing material, there are inevitable drawbacks to this type of roofing system.
The main advantages of a built-up roof include its ease of installation, fire resistance, and elemental protection. BUR is highly durable and can last decades in the right weather conditions. Seamless layers of asphalt and reinforced fabrics provide a watertight seal that is much less likely to leak than other roofing materials. A layer of stone provides a naturally fire resistant surface that also protects the underlying materials from UV damage, a characteristic that is not present in other flat roofing systems such as TPO.
Some downfalls to getting a built-up roof include the higher cost and added weight. Stone is a heavy material, which may or may not be a problem for your roof. However, the layer of gravel is one of the most important aspects to a BUR, providing the durability that a roof requires. Also, the cost of BUR materials and labor is generally higher than comparable roofing systems, such as single-ply membranes.
Built-up roofing contractors?
There are many built-up roofing contractors out there, and finding the best company for your needs can be daunting. When it comes to roofing projects in Los Angeles and Orange County, Southland Roofing Inc. will assist you with your roofing needs, offering expert general contracting services throughout Southern California. We work with all types of commercial establishments as well as residential properties. Our diverse team of construction professionals will do whatever it takes to help you meet your project goals, whether they are short-term or long-term. Contact us today for a free roofing estimate and to see how we can serve your roofing needs.