Trench Drains and Slotted Drains for Parks, Patios, & Pavilions

Pedestrian applications are found everywhere including parks, churches, sidewalks, retail shopping, condominiums, office complexes, restaurants, etc.   The systems used in these applications vary greatly due to budget, design flow, debris, pedestrian types, and location.

Pedestrian rated trench drains come in many different grating patterns and can often be customized to fit with the architectural style.  The materials range is broad due to the insignificant loading.  Often stainless steel, brass, cast iron, or even plastics are used.  The design requirements are driven more by aesthetics than by function in many cases.

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Design Considerations

Sizing the drain

  • Drain size can vary greatly in these applications so be certain of the flow requirements and debris loading when selecting a product.
  • Design trench drains to flow at capacity as much as possible to achieve higher velocity flows in trench and flush debris out of the system
  • For more details on properly sizing trench drains go to hydraulics.

Choosing the channel

  • Typically a precast trench drain system is used in these applications for the ease of installation.  Light loading does not warrant a heavy duty trench channel or frame.  Fiberglass or plastic bodies are typically used.
  • Pay close attention to the exposed frame at the top of the system to ensure the color and material match with the grate style that is chosen.
  • Sealing channel joints is not critical unless chemicals will be entering the trench drain.  If you do have chemicals you will want the joints properly sealed.  If you want this done properly you must specify the sealant method and stress to the contractor that this be done properly.  Metal channels should be welded water tight with a continuous bead.  Polymer concrete and Fiberglass channels should be properly prepared by roughing up the joint and then using an appropriate two part sealant.  HDPE channels should be welded together with a continuous heat welding process.
  • Applications that will see severe temperatures or changes in temperature should have similar thermal coefficients of expansion to that of the surrounding concrete encasement. One of the most prominent failure mechanisms for trench drains that receive foot traffic only is due to differing thermal coefficients of thermal expansion (especially when long trench runs are involved).  When the channel grows at a different rate than the surrounding concrete the channel material is stressed and eventually will fail.  This is always a factor outdoors and sometimes inside if fluid temperatures are elevated.  For more information see material properties.
  • Make sure that the outlet properly matches the design flow capacity.

Selecting the grate

  • Be sure that your loading is only pedestrian.  Hand trucks, carts, wheeled luggage, and constant high heels can place more severe loading on the system and require a heavier duty system.
  • Aesthetics are a factor in many designs and can be handled with several custom options such as custom cut grates, etched grates, custom finishes (such as nickel or bronze finishes), or custom materials.  You may want to select a heavier duty grate than needed based solely on how it looks.
  • Grates should be ADA compliant in any public building.  ADA requires that the grate spacing be no more than 1/2″ wide in a perpendicular direction to the primary travel direction.
  • Heel proof is another term that is common in the industry.  This term is generally accepted as 1/4″ wide openings.  Note that the smaller the hole the more likely it is to get clogged.  When selecting a heel proof grate the open area is very critical.  The more open area, the less likely it is to get completely clogged.  Heel proof grates should be avoided when catching water moving rapidly across steep slopes.
  • Ensure all grates are properly locked into place.  In areas where theft is a concern or where grates are particularly expensive you should insist on a tamper proof locking device.

Designing the layout

  • The layout can be simple or quite complex depending on the job specific requirements.
  • On long exterior runs take multiple bottom or side outlets in order to minimize the depth.
  • For radius trench drains it is important that you select a supplier before you complete the design.  Few companies offer this type of design and the cost will be significantly more.  If this cost is not figured properly in the design and bidding phase it can be an issue at a later date.