The U-shape of a plumbing P-trap provides a liquid seal to stop sewer gases from rising up into the homeland is installed at each plumbing fixture drain. But a building trap, also called a running trap, could best be described as 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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Here’s links to a collection of our other blog posts about PLUMBING PIPES:

• How can I protect my pipes to keep them from bursting during a hard winter freeze in North Florida?

• Can galvanized steel pipe still be used for new water lines in a house? 

• How can I tell if I have cast iron pipes in my house? 

• Why can't a sanitary tee be used for a horizontal-to-horizontal drain pipe connection? 

• What is the difference between green and white sewer drain pipes?

• Is a washing machine drain hose required to be secured at the standpipe?

• What are the abandoned pipes sticking out of the wall in my house?  

• What are the code requirements for plumbing vent terminations?

• What are the code requirements for layout of drain piping under sinks?

• What causes a gurgling sound when a bathtub or sink drains? 

• What is a "combination waste and vent" in a plumbing system?  

• What is a galvanized nipple?

• What are the pipes sticking out near my water valves?

• How do you accurately find a broken water pipe leak under the floor slab?

• What is the difference between water pipe and sewage (waste) pipe? 

• Are plastic pipes (PVC, CPVC, and PEX) safe for drinking water? 

• Is a hot water faucet handle required to be on the left? 

• What is a dielectric union? 

• What's that powdery crust on the pipe connections at the water heater? 

• If all the plumbing drains have water in them and you can still smell sewer gas, what's causing the problem?  

• How can I tell what type of plumbing pipe I have?

• Why is there a flexible accordion pipe under the sink? 

• What is a P-trap?

• Why is old galvanized steel water pipe a problem for homebuyers?

• What does polybutylene pipe look like? Why is it a problem? 

• Which water pipes are an insurance problem and possibly uninsurable?

• Can you connect CPVC pipe directly to a gas water heater?  

     Visit our PLUMBING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.