How to Purchase a Replacement Flat Roof Drain



Flat roof drains are often subjected to heavy weathering and regular wear and tear. As a result, their parts—including domes, rings, sump pans, and clamps—sometimes break, crack or rust over time, and need to be replaced.

To purchase a replacement part, you need to know the make and model of your original drain. To start, it is best to look for any raised or stamped part numbers that may be visible on the old ring or dome.

Unfortunately, if the drain has undergone extreme damage, this can be difficult to determine. The good news is there are ways to find out this information by looking at the drain’s color and dimensions.

Below, we’ve outlined the drain characteristics that will help you identify the make and model of a roof drain, which can then be used to purchase a replacement part.

Note: This post is specific to cast-iron roof drains, as PVC-roof drains vary greatly by manufacturer in size and application styles. Contact Hy-Tech Roof Drains for help finding a replacement drain or part.

Roof Drain Colors

The easiest way to identify the roof drain’s manufacturer is by color. Each of the four largest roof-drain manufacturers uses a unique color for its products.

  • Smith—Yellow or “Mustard”

Each drain manufacturer is represented in the image at the top of this post.

Drain Ring Sizes

Roof Drain SizesTo help find the model, next measure the drain ring size. There are 5 ways to take this measurement:

  • 4-Bolt Ring: Measure the bolt slots directly across the ring at 180 degrees.
  • 3- or 5-Bolt Ring: Measure the distance between neighboring bolt slots, as they go around the inside of the drain ring.
  • Inner Diameter (I.D.): Measure the distance between the ring’s inside edge of the gravel stop, directly across at 180 degrees.
  • Outer Diameter (O.D.): Measure the distance between the ring’s outside edges at 180 degrees. Include any lip or flange that extends beyond the gravel stop.
  • Lug Style: Lug style drains are measured the same as bolt-style drains, except the measurement is taken from the center of the pad’s dimple (Lug style drains are exclusive to Josam).

Roof Drain Dimensions

The following measurements and connection types can also help when finding a roof drain make and model: 

  • Sump Bowl Size: This is the bowl-shaped underside of the drain that funnels water into the outlet pipe. From the bowl rim to the opposite side, the most common sizes are 8, 12 or 15 inches.
  • Outlet Diameter: The drain outlet attaches to the building drain leader. Standard iron outlet pipe diameters is typically 2, 3, 4, 5, 6, 8, 10 or 12 inches.
  • Outlet Connection Type: Common connection styles include: no-hub, iron pipe (or threaded), caulk (used for lead connections) and “push-lock” (or gasketed).

Once you have the dimensions and details outlined in this post, either call Hy-Tech Roof Drains at 800-635-0384, or use our Roof Drain Wizard to find the exact roof drain you need.