Association of Home Appliance Manufacturers
Install Plumbing Pipe Indoors
Installing piping indoors means having to deal with structural barriers. In well-designed homes, most plumbing can be hung below the ceiling joists, either in a soffit near the center beam or in a utility room with a dropped or exposed ceiling. But on most jobs, you'll be faced with the problem of cutting into structural timbers. Knowing which timbers can be disturbed and how much you can safely cut from them becomes important.

The first thing you must do is determine whether the timbers in question are load-bearing or not. In many cases, only the outside walls and the wall above and below the center beam support the structure. Other than that, the wing walls on either side of a stair may carry a load, as may some walls on lower floors that run perpendicular to ceiling joists. Walls running parallel with floor and ceiling joists are generally not load-bearing. As a rule, the more unconventional and spread out a home's design, the more bearing walls are required.

In more cases than not, you'll be able to run your drainage lines along the center beam of a house, just under the floor joist. You can then branch up into the joist spaces and travel above ceiling level to the fixture locations. The line along the center beam can then share a space with the furnace duct and can either be left exposed or boxed in as a finished soffit.

In any case, a few guidelines apply when cutting into structural lumber. As a rule, you should never cut more than the center one-third of a floor joist. The top and bottom thirds must remain intact. If the pipe will take too big a bite out of the joist, you'll have to find another way. If you must cut the center of a joist, make the cut as close to a support wall as possible. Never, under any circumstances, notch the bottom of a joist.

When it comes to drilling pipe holes through vertical studs, leave as much lumber as you can at the edges of the studs. As with joists, avoid notching studs. In most cases, you won't be able to save two-thirds of a stud, especially when drilling for 1-1/2 or 2-in. pipes.

In fact, the hole for a 2-in. pipe will leave barely 3/8 in. remaining on each side of a 2 x 4-in. stud. This is unavoidable, but make your hole as small as you can. Figure the outside diameter of the pipe plus 1/8 in. for expansion. As for sole plates and top plates, you can usually cut those without concern. If pipes will lay within 3/4 in. of the face of stud, nail a protective strip of sheet metal over that area to shield it from drywall nails.

Written by Merle Henkenius.
Rerpinted with permission. Copyright HouseNet, Inc.

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