Close this search box.

How to Handle Parking Garage Drainage in the City of Austin

Depending on your jurisdiction, handling the drainage of water from parking structures can be a tricky proposition. WGI can help.
Parking Garage Drainage

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.


Sand Oil Separator

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.


Grate Inlet

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)

Share this post

Share this post

Learn more
about our


Single Duct VAV Box

Which Terminal Unit (VAV Box) is Right for Me?

Terminal units are an integral piece of an effective multiple zone VAV system, and selecting the appropriate type for your application will provide energy savings and a high level of thermal comfort.


You’ve been searching for a place like WGI. We look forward to meeting you soon.


Enter your zip code, and we’ll personalize your experience with local projects, office locations, team members, and more.

WGI's success starts with our Associates

WGI supports its associates with meaningful opportunities for growth, strong benefits and perks, while we work collaboratively with clients and co-consultants to shape and improve communities.

Our Team in Action

Join the Team

WGI is a dynamic organization with opportunities nationwide for engineers, land surveyors, landscape architects, environmental scientists, and architects.

Find a team member:

Let's talk about your next project.