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In the flat roof industry, what are commonly referred to as rubber roofs are in fact asphalt based products which have been modified with chemicals to "rubberize" them, hence the name "Modified Bitumen" (bitumen is another word for tar). These products are excellent when installed properly, adhering to the manufactures guidelines.
Torch Applied APP:
Historically this is the most common method of application. In this application, a propane torch is used to melt the bitumen on the back of the roll which, when cool, makes a very good bond to your roof substrate.
This method is not legal in NYC due to the great number of fires that have occured from careless or poorly trained contractors.
Cold Applied SBS:
This is essentially the same system as APP above with the exception of the need for torches. This material comes in both smooth surfaced or granular surfaced (small ceramic particles in black or white). The granular surface is much like the common shingle surface and never has to be coated with aluminum paint. This cold applied SBS material has no bitumen on the back like APP, instead it is set in a bed of cold adhesive. This system is much thicker than others and generally outlasts most other systems.
Hot Asphalt Applied SBS:
This system combines the best of both systems outlined above. It is the oldest and has been time tested and proven more than any other system. This system is essentialy the same as Cold Applied SBS, but, it also has the advantage of being set in a bed of hot asphalt, which is pumped to your roof from a kettle on the ground. While Hot Tar roofing has been around for over 100 years, we now have the benefit of "rubberized" SBS products to use in conjunction with these tried and true methods. A Hot Asphalt roof is more expensive than most roof systems, but, if it is within your budget, it is definitely worth it in the long run.
Rubber Roofing:
There are several real rubber roofing systems that are very hard to beat on a flat roof. EPDM Roofing Systems is one such system that provides 15 year guarantee against leaks. The material is similar to a tire inner tube and is made by Firestone, General Tire and most other rubber manufactures. These systems are glued directly over 1" foam insulation and when completed your roof becomes a water tight, sealed area. The material is 10 feet wide and 100 feet long, so the average house only has 2 or 3 seams, as opposed to 20 - 25 seams with other systems. This is a worry free roof and has been seen last upwards of 30 years.