There are as many shapes of a roof as there as many different types of roofing material. The roof shape that you eventually end up choosing for your home is also just as much dictated by the climate, the roofing materials available, the roofing material cost, and your personal style.
In contrast to the usual shape of a typical roof that is sloped in form, a flat roof is literally just as its name implies – flat. It is horizontal or almost horizontal.
Below are the major types of flat roofing material that you can choose from to coat your roof. Knowing the pros and cons can guide you in choosing the right flat roof coatings.
Hot-Tar-and-Gravel or BUR (Built-Up Roof) Flat Roofing Material
This is the most traditional of all flat roofing material types. Assembling it is like assembling a three-tiered cake: three, or even more, plies of water-proof material are alternated with hot tar and then carefully ballasted by a layer of smooth river stone or gravel.
The advantage of using gravel as a “flat roof coating” is that it is such an excellent fire retardant. Also, not only is it the cheapest from among the other types, it is the ideal flat roofing material for windows and decks that overlook the roof.
Of course, there are known setbacks when using BUR. Tar and gravel combined are very heavy. As such, BUR joists have to be strengthened to carry the heavy load. Upon installation, the overpowering smell of tar and gravel could become very offensive. Not to mention very messy because of its sticky texture.
Using BUR is definitely not recommended when there are already occupants in the house. Inhaling it could even cause health problems.
Further, if there is pooling of water in a BUR, water penetration could not be prevented with these types of flat roof coatings. Not ideal for colder climates as it has the tendency to sag after a long time.
Modified Bitumen Flat Roofing Materials
A bitumen is a term called to the combined flat roofing material made of coal tar pitch and asphalt products. In the 1970s, bitumen has been modified by the Europeans when the lower performance standards of roofing asphalt have been the cause of concern. The US eventually followed suit and modified bitumen as flat roof coatings.
In ordinary language, a modified bitumen is a hybrid BUR. It has the benefits of a BUR, combined with the added strength, flexibility, and UV-resistance of a modified membrane consisting of an asphalt-polymer blend.
This flat roofing material is usually applied to roofs by heating up the underside of the roll (the adhesive material) with a torch. This is often referred as torch down roll roofing.
Latest developments in this modified bitumen flat roof coating now involves a peel-and-stick system that is relatively safer and easier to use and without the risk of a fire hazard.
The peel-and-stick version of the modified bitumen is a good choice as it can easily be installed by the homeowners themselves. It’s light in color, making it reflect heat and cut down on energy costs. It’s neither too expensive nor too cheap.
With the non-peel-and-stick version of this flat roofing material, the process of torching down the material is obviously a fire hazard and not recommended when the house is occupied.
Rubber Membrane Flat Roof Coatings
Ethylene propylene diene monomer or EPDM rubber roofing material is a flat roofing material commonly used in single-ply roofing projects. It is readily available and very simple to apply. Its material is long-lasting and UV-resistant. You can use fasteners, ballasts with stone, or glue to keep it in place.
The good thing about these kinds of flat roof coatings it is that residential owners can install it themselves. It is also a low-cost flat roofing material.
The problem with EPDM rubber roofing materials is its standard color – black. This black material absorbs heat, unlike the modified bitumen. If you opt to have light-colored coatings, which are highly recommended in warm climates, it adds up to the total roofing material cost by at least 30%.
In general, compared to the different types of roofing material, flat roofing material should last long if properly installed and maintained. On the average, flat roof coatings can survive for 10 to 25 years.