There are many advantages to constructing flat roofs on commercial buildings. Firstly, the economic value makes a flat roof design extremely affordable. Also, commercial buildings often require mechanical and electrical equipment for such things as heating and air conditioning, making a flat roof the ideal location to house such large units. Repair is often easier to perform on a flat roof, and when the building is a high rise, that’s definitely a plus. This article will discuss the two most popular types of commercial flat roofs, giving the benefits and downsides to both.
Built-Up Roofing (BUR)
If you’ve seen a flat roof on a commercial building, chances are you’ve seen built-up roofing, also called a BUR roof. It is the traditional “hot tar and gravel” design. This type of roofing gets its name of “built-up” by the number of layers of bitumen (asphalt or coal tar) used to create the roof. A framing structure holds layers of moisture barriers and waterproofing laid in a criss-cross pattern. While traditionally the materials have been a form of tar paper, fiberglass sheets have come more into use in recent years. The actual bitumen is made of hot tar and gravel or other aggregate materials such as sand, white marble, and lava rock. Professionals measure BUR roofing by the number of layers which comprise the total structure, the higher number representing high quality.
The two major advantages of BUR roofing is it is the most cost-effective to install, and the gravel is an excellent fire retardant. The downfall to BUR roofing is the excessive weight of the materials requires a very sound structure on which to build. In addition, gravel can, over time, get loose and clog gutters or drains, and the design makes finding leaks difficult. However, repairs to BUR roofing can be done in patches, saving time and expense on replacing large areas.
Single Ply Roofing
The immediate difference Single Ply Roofing has over BUR roofing is, literally, the single layer used to create the roof. This is done with a membrane, usually made of rubber materials, and may be as thin as.045 to.090 inches. Membrane-style roofs are designed to have a long lifespan and are known to be extremely water-resistant. They come in several varieties, but most are made from synthetic rubber (EPDM), poly-vinyl chloride (PVC) or TPO (thermoplastic polyolefin). Installation varies greatly from BUR roofing, as the Single Ply materials do not need separate layers of waterproofing. The Single Ply can be installed directly over the roofing frame. To allow for a more green and energy efficient roof, additional insulation can be added under the membrane. The last step of installation involves bonding the seams of the membranes together to avoid leakage. This is usually done by either melting or chemically bonding the membranes to one another.
Without seams, the membrane can comfortably expand and contract in weather changes. With this flexibility, the material avoids leaks or cracks. Repairs on membrane roofs are performed easily with patches as well, however, locating the leaks is often far more difficult than with BUR style roofing. The material is considerably lighter than the gravel used in BUR roofing, but it does have more of a likelihood of puncturing. The EPDM roofs are cheaper, but the material is black, so an additional layer of white (especially in Southern regions) is often needed to aid in reflecting heat which otherwise is absorbed by the material’s natural coloring.