What Is A Roof Drain?

The Plumbing Code Definition

OK, so what is a roof drain? Let’s take a look at the authority on the subject which is the uniform plumbing code. 

The Uniform Plumbing code reads as follows:

“ROOF DRAIN: A drain installed to receive water collecting on the surface of a roof and to discharge it into a leader, downspout or conductor.”

I would have been a bit more specific on the description. A type of drain (as there are many) that is installed on a flat roof that is designed to receive rainwater collecting on the surface of  a flat roof and to discharge it into a leader, downspout or conductor.  These three words are synonymous and simply mean the vertical piping. 

Ok, so the simplicity is that a roof drain prevents rainwater from ponding on any flat roof by draining it away to the ground.  Excellent. we’re glad it does. 

Model SCP custom roof drain pans is designed to lower or sump the Frank Pattern™ Cast Iron Combination 8 1/2″ Diameter Roof Drain

What are the different types of roof drains? 

There are two main categories: 

  1. Primary or main roof drains
  2. Overflow or secondary

While there are many variations of these, they all fit into one of the categories. But before I address that issue I’ll define these and their purposes.

The primary (main) roof drain 

Model LSP roof drain sump pan is designed to lower or sump a 15

HOW DOES IT WORK? The primary roof drain is a single roof drain and it does all of the “heavy lifting” or most of the work in the roof drainage system. They are designed to be continuously in service and for this reason it is vital to prevent stoppages and make sure that they they are kept free of all debris.  

All of the primary roof drains are connected together on the same line and are not connected to any other part of the roof drainage system with few exceptions. They are tasked with draining the rainwater to the ground or another disposal location (like underground). This is called “conveyance” in the engineering circles and is an extremely important concept but we will address that in another blog.    

What is an overflow roof drain? What does it do? 

The overflow roof drain always has a 2″ water dam connected to it which looks like collar. This can be an external water dam that encircles the dome or it can be an internal water dam that is inside the dome. These are pictured above. 

What’s Their Purpose? 

It allows the water to pond on the roof  a maximum of two inches before coming into service. This is a plumbing code requirement. The overflow or backup roof drains protect the flat roof from caving in under the weight of standing rainwater should the main drains become clogged with debris.  

More Info Coming Soon

What Are The Various Components That Comprise A Roof Drain?

What are flat roof drains made from?

UPC (uniform plumbing code 1102.1). Roof drains shall be constructed of aluminum, cast iron, copper alloy of not more than 15% zinc, leaded nickel bronze, stainless steel,ABS, PVC, polypropylene, polyethylene, or nylon and shall comply with ASME A112.3.1 or ASME A112.6.4.  

All of the roof drains on the market comply with these requirements. If you find one that doesn’t, don’t use it. 

Dome strainers required

Roof drains shall have domed strainers. Exception: roof drain strainers for use on sun decks, parking decks, and similar areas that are normally serviced and maintained, shall be permitted to be of the flat surface type. Such strainers shall be level with the deck. 

Dome strainers are included with the roof drain. Manufacturers provide a choice in materials generally as a special order. These can be made from aluminum, stainless steel, brass, ABS, PVC (plastic). Review their specs for the exact offering. 

Roof drain flashings

This is important….more to come

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