Flat roofs are one of the oldest roofing styles. They are most common in many places of the world but especially where there is very little rain, such as traditional homes in Israel. One interesting note is that they are becoming more popular here in the United States; they are indeed re-gaining popularity in modern architecture. Yet the question remains: why use this design and can it offer the protection currently provided by conventionally sloped-style roofs?
As the name implies, this is a flat roofing system; however, the name is actually somewhat of a misnomer as this style does require a slight slope to effectively drain rain water. In places where rain is scarce, most flat roofs are constructed using masonry and concrete. In the United States at locations where there is a lot of rain and snow, concrete will not suffice and waterproof materials must be used to prevent water from pooling and actually seeing through normal roofing material.
There is a choice of materials available as well as various configurations to use in the construction of a flat roof system; however, the traditional building method of using tar and gravel is still the method that is generally preferred. The decking consists of a thick piece of plywood to support the rest of the materials that will be placed upon that support. Several layers of an interwoven fibrous material called plywood sheets will serve as reinforcement. Hot tar is moped onto the structure at each interval of the layering process, creating a water tight seal. On the final application of tar, fine gravel is applied to protect the tar and prevent it from cracking from constant exposure to sunlight.
As previously mentioned, there is a wide array of materials that can be used in the construction of this type of roof.
- Asphalt – Asphalt is a byproduct of processing crude oil into petroleum. It must be boiled to be easily applied, making installation rather messy. When properly done, the finished product is a roofing system with a long-lasting, water-tight seal. Because asphalt surfaces tend to become brittle and dry due with constant exposure to the sun, mineral granules or fine gravel are applied for protection.
- EPDM – Ethylene Propylene Diene Monomer is a type of waterproof membrane that is a synthetic type of rubber. Installation is easy as it only means unrolling the rubber, aligning the edges and sticking the pre-applied adhesive in place.
- Bitumen – Modified bitumen is also an asphalt-based product that has been modified to enhance its characteristics. Modifiers such as APP (Atactic Polypropylene) and Styrene Butadiene Styrene (SBS) are added to improve its flexibility and come in pre-cut sheets for easy installation and handling.
- PVC – Polyvinyl Chloride is another type of membrane that is derived from crude oil. It is well-known for being a strong and inherently fire-proof material. The material comes in manageable rolls, allowing for easy handling and cutting. Once the edges are heat welded, a bond is created that is stronger than the material itself.
Advantages and Disadvantages
One of the largest advantages of a flat roof system is affordability since there are no trusses to erect and work can be comfortably completed on the flat surface with little effort; the material itself is also quite low in cost. While asphalt can be quite messy to install, the effort does not compare to nailing individual shingles into place. Another advantage to this type of structure is the fact that attic space can be efficiently utilized. The height of the attic is approximately equal on all sides and be used as an extra room or a roomy storage area.
The downside of a flat roof is that it is sooner to water / ice damming. This occurs when ice and water collect on a low slope surface, causing water to be absorbed by the roofing layers, initially leading to penetration into the interior area under the roof. Therefore, it is important to consistently remove any snow build-up during winter weather as much as possible. Foot traffic should also be minimized to avoid cracking of the waterproofing layer.
Flat roofs are a low-cost, easily installed system. Care and maintenance should never be neglected in order to get the most service life out of this type of roof. Hopefully this article has provided some valuable information about the advantages and disadvantages of flat roofs on residential buildings!