Car Washes

Car washes obviously have a significant amount of water.  Many of the newer car wash tunnels are long and flat.  A central trench drain run the length of the wash bay is an obvious solution to collecting this water.

In some cases, other utilities such as water lines, soap, and mechanical movers are also run inside this drainage / utility trench making it a multi-purpose trench.  The trench can also be used as a place to remove sediment by using sand traps or catch basins with baffles.

A trench drain at a car wash rarely ever sees any traffic at all.  Usually the worst traffic is pedestrian traffic, so almost any frame and non skid trench grate will work.  The exception to this would be any drains that are located at the entrances and exits that receive vehicular traffic.


Sizing the drain

  • The drain size is determined by one of three factors;  The flow rate of the wash system, the amount of sediment that should be stored, or the type of utilities that need to be run in the trench.
  • If designing for the flow rate, these are typically very small and a 4" wide trench drain works in almost all cases.
  • When designing for sediment it needs to be determined how the sediment should be collected.  If it is to be collected in the trench drain then make sure it is large enough for a shovel and deep enough so that maintenance frequency is optimized.  If not, choose a small trench with the appropriate catch basin at the end to hold the sediment volume required.
  • If designing for utilities, simply determine how large the trench needs to be to attach or run all of the components.  Keep in mind any maintenance that may be necessary in the future and ensure that there is enough room to perform these tasks.  In some cases, we have seen these trenches 3' or 4' wide and equally as deep.

Choosing the channel
  • For a car wash application, the channel can be almost any material because of the infrequent loading on the trench.  The most common are a precast fiberglass trench or a concrete forming system.
  • The frame can simply be light duty, unless it is at the entrance and exit and will receive traffic.  In these applications it is best to use a roadway product with a heavy duty frame and grate.
  • All of the system components need to be corrosion resistant because they will be constantly exposed to a wet environment.

Selecting the grate
  • Grates are typically light to medium duty.  
  • The most common grates that we see are fiberglass, ductile iron, and galvanized steel grates.  For narrow trench widths the ductile iron grates are very economical and will last a lifetime making them a good choice.  For larger trenches that combine utilities the fiberglass or galvanized steel are the most common.  Fiberglass grates offer a non-skid grit surface that is nice in wet applications such as this for safety of the employees.

Designing the layout
  • The layout is typically very simple.  A single run that either slopes to one end or slopes to the middle.  In many cases there is a catch basin which houses a pump.  The pump evacuates the water from the system.