Trench Drain System Selection - ACO SWM
United States


Grate Selection

Trench Drain System Selection

A drainage grate’s primary function is to let water enter the trench drain system efficiently. Grates have to remove the quantity of water specified and be strong enough to withstand traffic without collapsing.

When choosing a grate, the following should be considered:

  • Water intake capacity
  • Loading
  • Material – durability and aesthetics
  • Slot style
  • Locking
  • Legal requirements:



ADA Requirements are set out in The Americans with Disabilities Act of 2010, Section 302.3

Where grates are used within walking surfaces, the open slots should be no greater than 0.5 inches (12.7 mm) wide in one direction. Where the length of the slot is greater than 0.5 inches, the opening should run perpendicular to the main direction of traffic

The diagram shows the slots perpendicular to the flow of traffic; this helps prevent wheelchair wheels and walking aids becoming trapped or slipping on the grate surface.



Slip-Resistant – ACO has tested grate patterns for slip resistance using the widely accepted pendulum test.

Pendulum test – A pendulum is swung over a wet surface and measures surface frictional properties. Test results are given a BPN value – typically values in excess of 24 would be used (24 and under is regarded as high slip and skid potential).

ACO recommends selecting a grate with the similar BPN values as the surrounding pavement finish. Pavement slope water, presence of surface contaminants, etc. can also negatively affect slip and skid resistance. Ask ACO for BPN reports if needed.

Other tests exist, such as the Variable-angle ramp test and horizontal pull test and can be carried out as necessary if required for specific projects




For applications where high stilletto heels are commonplace, ACO recommends grates with openings of 0.25″ (6.5 mm) or less to prevent heels from becoming trapped, causing injury or falls.



Bicycle-Safe – AS 3996 – 2006 Clause 3.3.6

Standard AS 3996 – 2006 Clause 3.3.6 which specifies maximum slot length dependent on slot width for grates that are deemed Bicycle Tire Penetration Resistant.

The visual importance of drain systems is now more prominent.

ACO has introduced many different sized patterns and materials, including discreet drainage concepts such as Brickslot and EcoPanel.

Another innovative option is Freestyle – an easy and cost effective way to design your own iron grate.

ACO offers a surface and grate Visualizer; an online tool for designers to imagine each ACO Drain grate against a number of different surface types.


Decision Tree for Grate Selection:

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