What is a building trap?
Thursday, June 21, 2018
The U-shape of a plumbing P-trap provides a liquid seal to stop sewer gases from rising up into the home through plumbing fixture drains. A building trap could also be called a “whole house P-trap” because it is on the main drain line, usually in the crawl space under a house or buried in the ground just outside the home, and provides a single seal to protect the entire home. It dates back to the time before individual traps were required for each plumbing fixture, and has been prohibited by the building code for many years.
Here’s what the Florida Building Code (FBC), Residential Edition, says:
We came across one in the crawl space under an older home in Gainesville (shown above) yesterday, and consulted our plumber, James Freeman, about why a building trap would be installed in a modern-day plumbing system. “I would say that it was either installed by a very old plumber from up north or by someone who didn't know what they were doing,” according to James. “Probably the latter. They used to be required a long time ago up north. Even if that was the intention, it's not legal here, would have required a vent, and is in the wrong location. It's also going to cause clogs and needs to be cut out and straight piped.”
Obsolete building traps are a common cause of plumbing backups in basements of northern homes, and the cure is removal. We rarely see them in Florida.
For other prohibited trap designs, see our blog post What plumbing traps are illegal by code?
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