Ask the Builder: Relocating pipes, wires and ducts

Q. Tim, I need you to weigh in on a remodeling conundrum. Two plumbers and one handyman say that two plumbing vent pipes can’t be relocated to an exterior wall. I took the drywall off the back of a linen closet to open up the space for my soaking tub. I want to have extra space for candles and wine bottles.

I live where it can get really cold, and they say moving the vent pipes can be a problem. Can the vent pipes be moved, yes or no? Can I just cap them off below the floor?

Also, what about moving wires and ductwork? Can that be accomplished? What’s involved when moving all these utilities? – Suzanne B., Minneapolis

A. Many DIYers have experienced that “uh-oh” moment at some point in their remodeling escapades. You know, when they gleefully start to tear down a wall and find all sorts of unexpected things going up through and between the wall studs.

The fast answer for Suzanne is the vent pipes can be moved. The important question: How easy will it be to relocate the pipes?

That question can only be answered by a visit to the job site to see what framing is in the way and what additional demolition needs to be done to create a pathway to allow the vent pipes to drain any condensate back into the drainage part of the plumbing system. Local codes might require the vent pipes to be put in certain walls. That’s up to your local inspector.

Never cap off vent pipes. These pipes are vital as they deliver air into the plumbing system. Most people think that the plumbing vent pipe up on the roof is like a factory chimney that exhausts smoke. Vent pipes work in reverse. They deliver air down into the system each time you flush a toilet, drain a sink or run water into a fixture. The moving water not only pushes air ahead of it as it travels to a septic tank or sewer, but it also can create a vacuum as a slug of water passes a drainage branch within the system.

Vent pipes need to be installed just like regular plumbing drain pipes. They need to have a slope so that any condensation that does form in the pipes can drain by gravity into the plumbing system on its way to the septic tank or sewer. This same condensation can be a pesky problem in cold climates, as hoarfrost can choke off a vent pipe. This is why in very cold climates, the main vent stack is often full-sized and a 4-inch-diameter pipe. The larger pipe size means that much more frost must form to choke off the air supply.

Vent pipes on exterior walls in cold climates should be located in such a way as to be as far from the cold exterior wall surface as is reasonably possible. You want as much insulation space between the pipe and the outer wall to hopefully keep the pipe temperature just above freezing.

Electrical wiring also can be relocated in a remodeling job. There can be significant challenges, and the paramount thing to remember is neither you nor a worker should ever bury a junction box. If you have to create a splice to add additional wiring, the junction box must be visible. You can often achieve this in a closet.

I always wrote a note and included a small drawing in the junction box of what had to be done to move the cable. Trust me when I say a future electrician will cherish reading this note. It might help him diagnose some future problem within the circuit, as he’d have no idea that remodeling work might have happened 50 years ago.

Heating and cooling ductwork is, by far, the hardest thing to relocate. The size of the pipes and ducts is the first challenge. The second, more sinister issue is poor performance because extra fittings and ductwork need to be added to make the change.

The addition of a 90-degree bend to a typical heating or cooling duct line is like adding 10 extra feet of pipe. The air moving through a heating or cooling duct is very sensitive to extra friction caused by additional fittings or pipe. More friction equals less conditioned air being delivered to the room where it’s needed.

Be sure to have a frank discussion with your HVAC professional about this if the room being served by the ductwork is currently on the edge of being comfortable in extreme hot or cold weather.

If you’re building a new home or a large room addition, you can do a favor for yourself, your remodeling contractors and future owners of your home. Try to take as many photos of all the walls, ceilings and floors in your new home or room addition as possible before utilities are covered with drywall or insulation. Store these photos on a simple storage device like an SD card or micro-SD card. These are inexpensive and can hold thousands of photos.

Put this memory card in a plastic bag and label it. Tape this bag to the front or inside cover of the circuit-breaker panel. You have no idea how valuable these photos will be to someone in the future.

Subscribe to Carter’s free newsletter and listen to his new podcasts at askthebuilder.com.