What Is Positive Flat Roof Drainage and What Is The Relationship To A Roof Drain Sump Pan?

The Main objective...

Achieving positive flat roof drainage is VITAL and is the total objective on any quality flat roof drainage plan. 

At first glance you may say that this is a “given”. The only way to get a “positive” flow is by making sure that the roof drains are the lowest point on the flat roof. Being lower than the flat roof surface, gravity will then push the rainwater into the roof drain and convey it to a disposal point at ground level via the roof drain piping system. That’s how it should work but is not necessarily the case.

Technologies to achieve positive drainage

SUMP RECEIVERS: Roof drain manufacturers provide a flat plate sump receiver with their roof drains. This puts the roof drain flat on the roof. Further, when the roofer adds the roof covering to the drain, it becomes higher than the roof surface. This means rainwater must travel uphill to enter the roof drain. This is “negative” drainage and can have disastrous results. 

Wood sump boxes:  This has been the main method used by the construction industry for decades. The installer used wood products to build a sump box. This is a very laborious, time consuming and ultimately expensive process. 

TAPERED ROOFING SYSTEMS: This method includes laying insulation on the flat roof. It is generally 2″ thick but can be thicker. When the insulation approaches the roof drains, it is now 2″ above the roof. It is then tapered to the roof drain. This is an extremely effective roof drainage system and results in positive drainage. This is used for new construction and for recover projects. But, what if you have just a few low spots on the roof? Do you want to spend the money to completely reslope your flat roof? No as it would be very expensive. 

Necessity Is The Mother Of Invention

Roof drain sump pans are designed and engineered to achieve positive flat roof drainage. NO EXCEPTIONS

How could such vital technology be missing from the industry for so long? It’s hard to say why exactly. But the good news is that a plumbing contractor developed these products to work on nearly any roof. Who better to solve the problem than someone was confronted with the problem on a regular basis? This is probably the case with the development of new ideas and inventions. 

These products have passed rigorous field testing over a number of years and they work exactly as stated and will achieve positive drainage on every job, every time, no exceptions when installed correctly. 

In addition to being a major industry advancement, they are engineered to be EASY to install by the novice or pro in minutes, not hours.  

While used on new construction projects, they particularly shine on retrofit applications. After all that’s what they were originally designed for.  

Try them out for yourself. 

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