A Question from a Reader – Those Plumbers!

Q: I recently had a contractor provide an estimate for putting down a vapor barrier in my crawlspace. While he was down there, he found several places where plumbers had badly damaged the floor framing. Should I believe him? –Ashlynn K., Clayton, NC

A: Hi Ashlynn, Ask the contractor if he could provide pictures of the damage, preferably with adequate lighting. It’s entirely possible he’s being sincere; I have seen this happen in numerous instances over the years.

New Homes vs Old Homes

Plumbers installing supply and drain lines in new houses rarely do anything to compromise house framing. If they do, an inspector will pick it up before the house is put on the market.

However, in older houses, remodels and repairs occur fairly often. Unfortunately, plumbers or HVAC installers sometimes damage your framing.

Good Plumbers vs Bad Plumbers

Plumbers need to situate pipes and supply lines at very precise angles, and in very particular places. GOOD PLUMBERS always make sure that their lines penetrate the floor in areas free of framing. If necessary, they even insist that framing changes be made to allow for clearance.

However, BAD PLUMBERS sometimes install pipes wherever it is easiest or most convenient. (Like in the top picture). When that happens, they remove nearly all of the joist’s strength. And, this creates a condensation-rot situation!

Bad Plumbers Do This, Too!

An even more frequent problem is “notching”. To traverse the crawl space at a certain height, they sometimes notch the bottom of a joist. (Pardon the quality of the picture below. It was taken from the prone position in a nightmarishly small space.)

plumbers often notch joists

It’s hard to see, but the plumber has cut a notch in the bottom of the joist!

This is almost as bad as the vertical bore. Cutting through the underside of a joist drastically reduces its “span” strength. That’s the amount of load it can carry over a specific distance. (Here’s a really comprehensive link for the informational span tables of southern pine.)

The proper way to handle this situation is to pass the pipe through a hole in the center of the joist. That way, material around it on all sides can easily compensate for the hole.

However, feeding pipe through a series of these holes in a tight space is often logistically impossible. Rather than finding a better way, bad plumbers take the easy way out. They notch the joists instead.

Pro Tip

If you have notched joists in your crawlspace, the problem can be mitigated by “sistering”. That means attaching a companion piece above the notch to help carry load.

lumber sistered notch wood repair

I “sistered” this joist to compensate for the notch.

The process really isn’t that complicated most of the time. But, it will greatly increase the strength of your floor system. Shoot a lot of fasteners in a continuous “W” pattern. That way, you tie the new member to the old one.

A More Complicated Fix

Carpenters occasionally shorten and bridge framing members to allow for drain line penetrations. Here’s a good animated video tutorial on how that is done.



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