Traditionally flat roofs would use a tar and gravel based surface which, as long as there was no pooling of water, was sufficient to prevent penetration.
However, these surfaces would tend to fail in colder climates, where ice dams could block the flow of water. Similarly, they tend to be sensitive to sagging of the roof reversing the subtle grading of the surface. Over the years, homeowners also realized that it can be costly to maintain them and repair them as well.
Modern flat roofs tend to use a continuous membrane covering which can better resist pools of standing water. These membranes are applied as a continuous sheet where possible, though sealants and adhesives are available to allow for bonding multiple sheets and dealing with structures penetrating the roof surface.
The technical aspect of those roofing membranes and synthetic rubber roofing compounds for flat roofs outperform gravel roofing materials and make roof leak detection far easier. These roofing materials are basically seamless and contain materials that resist UV degradation. Used mostly commercially, flat roof membranes also have many residential uses.
Let us find a simple way to describe the actual material. Have you ever seen how flat tires are fixed on a tubeless tire? The rubber patch is actually vulcanized to the tire’s inner surface with special solvents. The patch and the tire basically become one in the same. This is exactly how some of those new membranes work. As a roofer seams pieces together or makes cuts for flashings, they can actually weld pieces of material together and avoid penetration.
The installation of those synthetic membranes differs depending of the type of deck (wood, concrete, metal…). There is also a large variety of system available with additional plies or optional insulation (to create slope towards drainage area or simply energy efficient).
Don’t be tempted by the lower price to do a quick mop over of your existing asphalt roof. The price of re-roofing a residential patio flat roof is relatively low.
Asphalt is an old technology that had made its proof of being very reliable and easy to fix if repairs are necessary. The system is dependent upon expert workmanship for long term high performance. Excellent workmanship is hard to find these days so choosing the right roofing contractor will guarantee a long life to your roof. Be careful, this system will be prone to failure if not done by experts.
You can also find the use of those systems in many weak areas of a slope roof (chimney area for instance). Ever heard the word crickets? These are little hip roofs that are found behind chimneys. Membranes work very well here.
The synthetic membranes have many other benefits. Imagine being able to cover your house with just one giant piece of roofing material? Barely any seams to worry about! It is possible if you find the right roofer and get the right membrane. Some of the membranes come in widths up to 50 feet! You must remember that this technology is not really used much in residential work. In this case, some of the top performing materials are the synthetic rubber roofing compounds. These are commonly referred to as EPDM and single ply materials. The only disadvantage, I can see with them is that they are not DIY (do-it-yourself) friendly. In other words, you will certainly need to locate a professional to install them.
The use of modified bitumen flat roof and synthetic membranes in Florida has just about eliminated the need for gravel on roofs. Why? Because many of these new roof membranes are mopped or glued down to the roof. Not only that. If you can install a new flat roof without gravel, do it! It will make future leak finding much easier and with a longer life expectancy it will be worth your money. Leaks cause anxiety. Don’t get cheap when it comes to your roof. Buy the best and just relax.
Different flat roof system: details and specifications.
Asphalt Gravel Roof
Gravel used to be the most common system. They are referred to as asphalt and gravel roofs. Their use is not very recommended in newer construction as new systems tend to be more effective.
Asphalt Built Up Roof
Asphalt is an aliphatic compound and in almost all cases a byproduct of the oil industry. Some asphalt is manufactured from oil as the intended purpose, and this is limited to high quality asphalt produced for longer lasting asphalt built-up roofs. Asphalt BUR is the most common type of flat roof at this time. It is made up of multiple layers of reinforcing plies and asphalt forming a redundancy of water proofing layers. The reflectivity of built up roofs depend on the surfacing material used.
Drawback? As it ages, the asphalts melt point rises and there is a loss of plasticizers. As mass is lost, the asphalt shrinks and forms a surface similar to alligator skin. Asphalt breaks down slowly in water and the more exposure the more rapid the degradation. Asphalt also dissolves readily when exposed to oils and some solvents. Asphalt degradation is a growing concern. UV-rays oxidize the surface of the asphalt and produce a chalk-like residue. As plasticizers leach out of the asphalt, asphalt built up roofs becomes brittle. Cracking inevitably follows, allowing water to penetrate the system causing blisters, cracks and leaks. Unfortunately, compared to other systems, installation of asphalt roofs is energy-intensive and contributes to atmospheric air.
Bitumen is a term applied to both coal tar pitch and asphalt products. Modified Bitumens were developed in Europe in the 1970’s when Europeans became concerned with the lower performance standards of roofing asphalt. Modifiers were added to replace the plasticizers that had been removed by advanced methods in the distillation process. The two most common modifiers are APP (attactic polypropylene) from Italy and SBS (styrene-butadiene-styrene) from France. The United States started developing modified bitumen compounds in the late 1970’s and early 1980’s.
APP was added to asphalt to enhance aging characteristics and was applied to polyester, fiberglass, or polyester and fiberglass membranes to form a sheet good, cut in manageable lengths for handling. Usually applied by heating up the underside of the roll with a torch provided a significant fire hazard and was outlawed in some municipalities when buildings caught fire and some burnt to the ground. Another problem developed when a lack of standards allowed some manufacturers to produce goods with amounts of APP insufficient to enhance the aging characteristics. SBS is used as a modifier for enhancing substandard asphalt and provides a degree of flexibility much like rubber. It also is applied to a myriad of carriers and produced as a sheet-good in rolls that can be easily handled.
Cold applied liquid membranes
An increasingly popular choice for new roofs and roof refurbishment. No open flames or other heat sources are needed and the glassfibre reinforced systems provide seamless waterproofing around roof protrusions and details. Systems are based on flexible thermoset resin systems such as polyester and polyurethane. This is the less costly option (especially in residential), generally use for very small roof surface.