When performing design on many multi-family and office projects, many times parking garages are included as part of the construction. Handling the drainage of water from these structures can be a tricky proposition, especially in The City of Austin.

The layout of parking garage drains should be a collaborative effort between both the structural engineer and the pre-cast engineer (if applicable). These engineers are responsible for the layout and sloping of garage surfaces and providing the Plumbing Engineer with the final layout.

Storm vs. Sanitary

There are oftentimes 2 different systems involved in the draining of a parking structure; the storm system, and the sanitary sewer system.

A parking garage will oftentimes be open on the top and in some cases, the sides. Any drains serving surfaces on these open levels should be collected and taken directly to the site storm system. With parking structures that are partially open on the sides, it is important to review the circumstance with Industrial Waste Department in the City. They will make the final determination on the system these levels should drain to.

Drains serving enclosed parking garage levels should be collected and discharged through a sand/oil interceptor prior to entering the sanitary sewer system. The sand/oil separator will collect any water discharge off from cars, garage wash-down, or from other sources to remove any grit and oil that may be present.

Prior to passing through the interceptor, the drainage line shall go through an inlet grate box.  The grate box is a detail unique to The City of Austin.  The purpose of the grate box is to act as a trap for the garage drainage system, as well as a means to witness the proper operation of the system.  It is important to have a structural engineer design the box grating if placed in an area where cars may park on the box.

If the garage has levels below grade, it is oftentimes necessary to pump the outlet of the interceptor.  If this is the case, it is recommended to provide a dual pump system in case there is failure with one of the pumps.

In any case, the drainage from parking structures will require review by the city’s Industrial Waste Division and will need to be approved prior to obtaining a permit.  This can be a long review process, so it’s important to submit the pertinent sheets to the Department several weeks prior to the building permit submission.

Do you need expert assistance with your parking garage plumbing or drainage design? Looking for a client-focused MEP engineering firm that has done this before? Contact Us today to discuss your next project!

cover photo credit: Zero Style North Seattle (cc)