Measuring Rectangular Grates

Storm drain physical dimensions that are critical to successfully installing a Catch Basin™ Insert (CBI) filter.

Drain inlet type: Square or rectangular, flat, drop inlet

Fabco’s StormBasin™, StormSack™, StormSok™ and StormPod™ are all considered Catch Basin™ Insert (CBI) Filters. These filter products are designed to be installed under the grate of a typical storm drain inlet. In this position, any runoff water directed to the drain must first pass through the filter before it travels through the rest of the underground stormwater system. Catch Basin Insert filters can treat a variety of pollutants at this entry point effectively cleaning the water before it is combined with potentially clean water downstream

To properly fit a CBI filter to a grate and frame certain physical dimensions must be measured with some degree of accuracy. Measurements should be within a 1/16”

  1. Measure the overall Grate dimensions inside the frame. In the example above the Grate is 24” x 24” square.
  2. Measure the CLEAR SPACE inside the grate support ledges. In the example above this is 22 ½”. This grate and frame combination is square so the clear space can be defined by 22 ½” x 22 ½”.When an insert is installed into the frame it’s support flanges rest on top of these same Grate support ledges. The unit then hangs down or is suspended from the flanges below the support ledges and occupies most of the available clear space. With round and square StormSok and StormPod products the Clear space measurement is critical as these units have a fixed support flange size.While you are measuring the Clear space it is important to examine the walls of the drain (all 4) directly below the frame. The first 20” below the ledges would be most critical. Any object that extends from the wall beyond the edge of the support ledge could interfere with the CBI device. This could include: pipes, traps, concrete and brickwork. These points of interference would need to be trimmed back if possible at the time of installation.
  3. Measure the depth of the drain from the bottom of the support ledges to the vault floor
  4. Confirm whether the Grate has ribbing that extends downward from the bottom side of the grate. In the example above, both Grate images display vertical ribs that extend down causing the Grate to have a Rocker looking cross section.