Whenever you work on an old house, one thing is certain: there will be surprises.
Some surprises are pleasant -- like finding a perfect set of servants' bells in a boarded-up stairwell, or finding good wood floors under layers of carpet and tile. But some surprises are bound to be unpleasant -- like finding out you can't have a big family bath on the second floor and retain the elaborate molded ceiling in the living room below.
In fact, plumbing is a major breeding ground for uncomfortable surprises.
If you're redoing a house from scratch, a gut rehab, you may be able to get the plumbing to conform to your desires. But, if you're trying to preserve architectural details, or redoing only a portion of the house (a kitchen and bath remodeling, for instance), you are virtually certain to have problems serious enough to require some changes.
Randy's been working on a kitchen renovation where plumbing for a second-floor bath just above is causing trouble. He discovered, when he took out all the ceilings and walls, that the stack, or main drain vent to the roof, was right in the middle of space allotted for cabinets.
That's not the only problem: The house's owners want to raise the ceilings in the kitchen area as high as possible, and all of the plumbing pipes, drains and water lines, were just above the old, low ceiling. In addition, the original plumbing was not in good shape. One cast-iron pipe was cracked open -- the only thing that had kept it from leaking was that the crack was on the top side. It was clear to everyone that that plumbing would have to be replaced.
The first step -- the simple part -- was running new copper water lines to the bath. Water lines are tiny, just 1/2 to 3/4 of an inch, typically, in second-floor installations, so they're usually not a problem to fit in. If they have to cross a joist, it doesn't hurt the structural integrity to drill a 3/4 - or 1-inch hole for the pipe to pass through. Of course, the fewer holes in the joists the better, so the pipes run between joists wherever possible.
Drains and vents are a little more difficult to place. Putting a 3-inch hole in a 2-by-10-inch joist would weaken it, so 2-inch drain pipes have to run between joists or below them.
Water pipes, besides being smaller, can run level; water pressure will keep the water moving. But drain lines must slope 1/4 -inch per foot from the fixture trap to the main drain. That doesn't sound like much, but a tub with a drain that's 12 feet from the main drain would need a pipe that drops 3 inches. Three inches might not drop below the joists if it ran between them, but if it had to run under them, it would mean the ceiling would have to be at least 5 inches below the bottom of the joists.
If ceiling height is important, you should let your plumber know early in the process. Then monitor his progress. Remember that to contractors and subcontractors, time (labor) is money. They are justifiably reluctant to spend more than they have to. If they don't know about the ceiling heights, they may run pipes below the joists because it's easier than doing a lot of drilling. On the other hand, you don't want to mindlessly have the plumber drill through the joists, in case he's not as concerned as you are about weakening them.
In Randy's project, the drains ran parallel to the joists and could be moved out of the way. The wall where the cabinets were to run was moved into the room 6 inches, to allow space for the stack behind. That left only the problem of the vents.
Old houses frequently aren't vented properly, but it's hard to tell how bad it is until the ceilings and walls are out. In modern plumbing, vents carry exhaust and sewer gases up and out of the house. Vents also allow fixtures to drain properly -- sort of like putting two holes in a can to get it to pour freely.
In this particular case, while it turned out to be easy to move the plumbing, once it was moved it couldn't be properly vented, because it would mean tearing out ceilings and walls in rooms above the bath that were not part of the project.
To make the venting situation better, though not perfect, Randy had the plumber run as much venting as possible through walls already torn out, and then they were able to steal some space from the back of a closet on the third floor to join pipes into the main vent.
If you run into a complex venting or drain situation, you might consider inviting the local plumbing inspector to check it out and suggest a solution. But be prepared to accept a compromise that could mean altering where fixtures are placed, living with a lower ceiling than you'd like, or maybe even expanding the scope of the project to get into other walls and ceilings. And maybe the next surprise will be a good one.