Avoid These Waterproofing Failures for Decks and Balconies

by Cheryl Morgan

  • October 2nd, 2020 / 
  • Education

When building a deck or balcony as a way to add value to a home or business, be sure you understand the best available options and pay close attention to the details to avoid waterproofing potential failures.

Waterproofing Best Practices

There are many decisions to make when building or adding an elevated area to your building – here are some things to try and avoid and some best practices to follow to prolong the life of your waterproofing system!



Be sure your flashing adheres to certain specifications. Flashing needs to be 4” x 6” at all wall-to-deck junctions, have a 2” x 4” drip edge on all outside edges and flashing needs to overlap 4”- 6”. Flashing is very important to keeping water out of surrounding walls and the substrate.

Deck Rail Placement


All decks must have railings for obvious safety reasons, but if installed improperly, these necessary pieces pose a great risk for water intrusion. To avoid these issues, rail plates should be placed on top of the full waterproofing assembly, always avoid penetrations to the deck like nailing or screwing railing into the top, and best practice – install face mount railing.


Roof drains and deck drains perform differently. If you are installing a deck waterproofing system, be sure deck drains are being specified and used. Scuppers can be used in parapet walls if proper sloping allows the water to drain at the wall.

Parapet Walls

paraphet walls

If the balcony deck has parapet walls, you will need to utilize crickets to ensure proper drainage. This can be done in the substrate or by using a sloping compound. If the crickets are installed using a sloping compound, allow for proper screed elevations.



Interior elevations should always be higher than exterior elevations. The use of backup membranes is highly recommended as a means of extra protection. Be sure flashing is able to be installed correctly, proper hem flashing is installed under the door, and there is a minimum of ¾” elevation above the deck.

Recent Balcony Failure Case Study

Learn one of the biggest challenges we come across

In a Recent Waterproof Case Study

We surveyed several decks at an apartment complex in Orange County that had failed. The apparent culprit was the railing which was installed by directly puncturing on top of the waterproofing system. This allowed for the intrusion of water through these puncture areas causing the coating to bubble, leak, and fail.

Over 500 decks at this multi-family complex failed due to the incorrect placement of handrails. This expensive mistake could have been avoided by installing the proper side mount railing.

Did You Know Westcoat Offers Complimentary Deck Inspections?

Allow one of our Westcoat representatives to stop by and complete a job walk to see if your balconies and decks need assistance. If work is needed, we will supply three Qualified Applicators who have installed Westcoat before to give you a quote based on our assessment. Fill out the form below or contact us today to learn more.

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