Advantages & Disadvantages of Diff Roofing Systems
In today’s market, there are several different roof systems available, each with diverse strengths and weaknesses. Below, I will briefly explain each method, then list the pros and cons.
Thermoplastic And PVC
Pros – Superior quality in water ponding conditions. In the neighborhood of 30lbs, very lightweight roofs. Per hundred sq. Just ft. If a cool roof is needed, it comes in white or in many different colors for aesthetic concerns. Another plus of these roofs is that it is possible to order large custom designed field sheets from the factory, eliminating the seams sealed on the job site by the team. Ozone, algae and field resistant seams are 3-4 times stronger than seams filed with EPDM. The material also has a huge amount of versatility. And there are no toxic gases to contend with, because seams can be welded with hot air. Warranties are valid for both 15 and 20 years.
Cons – They are susceptible to discarded cigarettes, sharp objects dropped on the membrane, and broken glass from bottles thrown on the roof as a single ply (this occurs a LOT) I normally discourage customers from installing these types of systems if the roof has a lot of foot traffic or is readily accessible to unauthorized workers. In the past, material shrinkage on thermoplastic and PVC roofs was often a serious concern, but this problem has been alleviated by improvements in composition and development. Over time, but not to the point of collapse as in the past, these roofs still shrink.
Bottom line – Great roofs, especially on roofs that heavily contain water, as long as the roof is typically only accessible to approved personnel.
Asphalt Modified Bitumen
This roof is what a rubber roof is called by a lot of people, when it is simply made mostly of asphalt. It comes in 3 ft. wide rolls and is typically torched down with an open flame, but in some circumstances they can also be applied with hot air welders.
Pros – The greatest strength of these roofs, in my opinion, is how well they hold up to outside stresses. They handle foot traffic better than any other membrane, and, especially if they have a granulated surface, are difficult to puncture. In fact, these roofs are so hard that most insurance firms would not even consider hail damage like they do on other roofs (I have personally seen changed roofs completely pummeling with hail and come out completely undamaged)
Cons – Of these systems, the most apparent downside is that there is a seam every three feet, which allows for a LOT of seams. You’ll probably be fine with this method if you have a conscientious crew with a professional foreman who can ensure that every seam on the roof is triple checked. If not, in my experience, you can be pretty sure you can end up with leaks very quickly, long before the warranty expires. And wide ponding water areas on these systems would prematurely degrade the content.
Bottom line – This can be a good roof on a building that does not over-pond water with a good, seasoned crew. And if you have a building that has a lot of foot traffic on the rooftop, that’s probably the only way to go.
This device is applied with a broad spray unit, spraying two components of liquid (isocyanate and resin) When the liquids are mixed together, they expand 20-30 times and stick to concrete, wood , steel and most existing roof systems, but NOT to modified bitumen according to the manufacturers.
Pros – The roof is monolithic with no seams when completed, completely adhered and has insulating properties.
Cons – Full disclosure, I have little experience here in NE Illinois with such roofs. We’re not installing them, but with this device I’ve been on 9-10 houses, and all of them leaked badly, in a few cases within months of being installed. And when detected, leaks are very difficult to track down and difficult to fix, as repair materials do not stick very well to this surface.
Bottom line – I would not advise my clients to go this route when a fresh roof is required, based on my admittedly limited experience with this device.
Rubber roofs with ballast (Riverbed gravel or pavers) can be fully attached, mechanically fastened or weighed. They are flexible, suitable for many installations and have a long track record.
Pros – Rubber roofs are fairly low-cost, simple to build and repair. They are available in wide sheets to minimize the amount of seams in the field, and the membrane has quite a bit of versatility.
Cons – Field seams are not as solid on these roofs as thermoplastic roofs. The flashes and the edges of the roof appear to wear out quicker than the rest of the roof. In certain applications, shrinkage over long periods can be dramatic.
Bottom line – For a building owner, it can be a successful investment, but all of the requirements of a given installation must be carefully weighed. And good installation workmanship is important.
Spray Applied Roofing
Legally, these are not re-roofs, they are called coatings. They are referred to by some businesses as “re-ply” because you simply apply a ply to the current roof surface. There are numerous producers selling different goods with various formulations and requirements, too numerous to go thoroughly into here. If an existing roof has leaks, but has not progressed to the point of total collapse, they may be good candidates for this solution.
Pros – It can be extremely cost-effective, especially on roofs with a lot of projections and HVAC units on the rooftop. The material is pure white, which can reduce AC cooling costs dramatically in some cases (especially on metal roofs). Because this is known to be roof repairs rather than a new roof, there are also tax benefits.
Cons – The current roof must still be in a reasonably good shape. Your cash would simply be lost if added to a roof that has already collapsed. Often, because this substance is sprayed on, during the application process, all cars within 100 feet or so must be relocated, as this material would be extremely difficult if not impossible to extract from the finish of a vehicle. Some suppliers do not guarantee this material if the roof contains ANY ponding water. It can not be added to an existing gravel ballast roof.
Bottom line – If the current roof is in good enough condition to accept the coating, this solution can save a building owner a lot of money. Excellent solution, especially for metal roofs.
There are several different solutions to your flat roofing needs, as you can see. However, it is important to choose a roofer who suggests the best system for your unique roof and circumstances and not the best solution for your pocket. Be sure to understand why a roofer suggests a specific system for your project, and what system is going to be the best investment for you.