Maintenance Tip #2: Plumbing Traps (It’s a Trap!)
Today, we’re diving into something that’s not quite glamorous but is absolutely essential—
plumbing traps. Yes, those humble, U-shaped pipes under your sink are doing more than
catching dropped wedding rings and questionable gunk. They’re protecting your home from
a truly stinky situation.
Wait, What’s a Trap?
For those of you who didn’t grow up reading plumbing codes for fun (you lucky ducks), a
trap is the U-shaped section of pipe under a sink or drain that holds water to block sewer
gases from wafting back up into your home. Think of it as a watery force field—basic,
effective, and easy to take for granted until it’s not there.
There are different types of traps used in homes, but not all are created equal. In fact, one
type is illegal. Yep, illegal plumbing. (Bet you didn’t expect that kind of drama today.)
Enter the S-Trap: The Rebel of the Plumbing World
The S-trap looks just like its namesake: a winding “S” of pipe. It was once the go-to solution
in many homes, but today? It’s a code violation waiting to happen.
Why the fall from grace? Simple: S-traps are notorious for siphoning water out of the trap
when the fixture is drained, which breaks that protective water seal and—voilà!—you’ve
got sewer gases seeping into your home. Not exactly the ambiance you’re going for.
The International Building Code has since said “no thanks” to the S-trap, and for good
reason.
The P-Trap: The Lawful Good Hero
By contrast, the P-trap (also aptly named) is now the standard. It keeps water where it
belongs and helps ensure those smells stay buried in the bowels of the system where they
belong.
But even with a good P-trap, setup still matters. Let’s break down a common problem.
Pipe in the Wall? Or in the Floor? Let’s Talk Routing
In older homes, it’s not uncommon to find that the pipe inside the wall has rusted out.
Replacing it can be a pain—especially if you have to remove cabinets. So some contractors,
in the name of convenience, will reroute the pipe through the floor of the cabinet.
Is that legal? Sometimes yes, sometimes no. It all depends on the spacing.
Here’s the Magic Formula:
To ensure your trap is up to code, the distance between the trap outlet and the drain pipe
(we call this the trap arm) must be at least twice the diameter of the trap pipe.
Let’s do some quick math:
- Got a 2” pipe under your kitchen sink? You need at least 4” of trap arm.
- Got a 1.5” P-trap in your bathroom? You need a minimum of 3”.
- Only have 2.5” of space from trap to wall? No sweat—you can reduce the P-trap to 1.25”
and you’re back in the green.
Important: Regardless of size, the maximum distance for a trap arm is 30 inches. After that,
it’s just a pipe, not a trap.
Final Thoughts
Plumbing traps are one of those things that seem straightforward until they’re not. As a
landlord or property manager, it’s worth taking a second look at your setups—especially in
older properties. An improperly installed trap can lead to code violations, costly repairs,
and a lingering eau de sewer you really don’t want.
Next time you’re under a sink, remember: it’s not just a bendy pipe. It’s a guardian of indoor
air quality.