System Justification for Modified Bitumen vs. Single Ply — So, you’re getting proposals for a new roof system on your facility. If you don’t have a Scope of Work or a guideline for the new roof, you’re likely to get as many different systems as you have bidders.
So, you’re left with comparing prices rather than comparing comparable roof systems. In short; apples versus oranges versus bananas, not the best way to procure the best roof system for long term performance.
If the roofing system being proposed or requested doesn’t fit the particular application, we feel compelled to advise the Owner of our concern.
Single Ply roofing membranes have become very popular, and when used in the correct application, very successful. Spann Roofing has successfully applied thousands of square feet that are performing well. We continue to use and recommend this type membrane in various applications. An application where many HVAC units are present and roof traffic is high, in our opinion, is not the best application for a single ply membrane roofing system of any kind.
Let me start by speaking about roofing systems, the physics of wind uplift and the effects on those roofing systems. A roofing system is not simply insulation and a waterproofing membrane. The total system, which includes the deck system, has to be evaluated when considering new roofing. This is especially true when the project is located on the coast, like yours.
Most people have heard or said “the roof was blown off because of high winds.” The roof did come off, but it was actually “sucked” off by a low pressure created by high winds. As wind blows across a roof’s surface, it creates a low pressure area or vacuum over that surface. This vacuum is creating uplift of the membrane. A partially attached single ply membrane will flutter as the wind moves across it. It would resemble your shirt fluttering on a windy day.
If air can enter from the underside of the deck, such as with a plywood deck, the air pushes up and lifts the membrane as the low pressure pulls upward from above. After continuous cycles of this effect, membrane and fasteners become weakened and can let go, causing the roof to lift and eventually be “sucked” off of the building. Adding to this stress, if a cut, puncture or seam separation occurs, air gets under the sheet and lifts it off. Ocean front compounds this problem by having almost constant wind.
A modified bitumen system, although more expensive, has added safe guards against the ravages of the wind. First, the system is a redundant, multiply system that has total adhesion for each ply, making an almost monolithic covering of 200+ mils of protection versus 45 to 60 mils of a single ply.
The added protection becomes evident if a HVAC mechanic drops a tool or tool box on the membrane. Even if a puncture occurs in the cap sheet, the underlying multi-plies still keep the system watertight.
Our decision to recommend the modified systems is based on our many (50+) years of experience in roofing along the coast. There is an application for most all roofing systems on the market today. There are certain applications that are just not suited for a single ply.
Then why, you ask, is the single ply being proposed? There can be several reasons for contractors to propose a single ply. A single ply may be the only type roof the contractor installs. It could be the contractor feels that the only facet of your project that you’re interested in is a low price. And it could be the only type system the contractor is authorized to install in order to provide you with a workmanship and material warranty. This is another topic of discussion for later.
Please feel free to call our references. They continue to rely on our expertise and value added advice when it comes to roofing along the coast.