Building codes specify allowable sizes and locations for holes and cuts in studs. Here's a handy guide to those requirements that will keep your building standing tall.
You get two benefits when you build or remodel with wood studs. The studs provide the strength and framework for the structure, and the empty spaces between the studs serve an important function, too: They provide the perfect place—a veritable vertical freeway—to run pipes, vents, drains, wires and ductwork. The drawback? When you have to run pipes, ducts or wires horizontally through the studs, you often have to notch or drill holes—sometimes big ones—to get them to their destination. But you can't just drill and saw away. There are rules you have to follow for drilling and notching studs. Some rules help ensure the structural integrity of a wall. And others are aimed at protecting pipes and wires that could be damaged by screws, nails and other fasteners driven into a wall.
There are LOTS of building codes dictating just how large a hole or notch you can cut (Fig. A). The technical yet important rules are:
To appease the plumbing gods, the codes have made at least one notable exception: In bearing walls you can bore 60 percent size holes—as long as you double up the studs and don't drill through more than two successive pairs of these doubled-up studs (Fig. A). This allows you to run a short section of “drain, waste, vent” (DWV) pipe through a 2x4 wall without beefing up the whole wall to 2x6 dimensions.
There are other, less specific guidelines:
When possible, notch a stud near the top, rather than the bottom. Don't locate holes and notches near large or loose knots, and don't group too many in the same area of the stud. Finally, notch only when necessary; holes weaken it less than notches.
In areas subject to high winds, earthquakes or tornadoes, maintaining wall strength is particularly important. Furthermore, studs with too much “meat” removed tend to bow and warp. Your building inspector will be on the lookout for overzealous notching and boring, so follow the rules.
In reality, few walls ever out-and-out collapse during everyday duty from being riddled with too many holes and notches. But there are LOTS of cases in which unprotected or inadequately protected pipes and wires have been nicked and punctured by screws and nails. Any plumber or electrician will tell you that's what you REALLY need to watch out for!
The National Electrical Code requires holes containing non-metallic cable (often called Romex) or flexible metal-clad cable (the type you buy with the wires already in it) be set back 1-1/4 in. or more from the edge of a stud (Fig. A) to protect the wires from nails and screws. (The 1-1/4-in. screws and nails used to secure 1/2-in. drywall penetrate the studs about 3/4 in.) Most electricians keep their inspector happy by drilling 3/4-in. holes dead center on a 3-1/2 in. wide stud. This gives them a hole large enough to run two electrical cables and leave 1-3/8 in. of protective wood on each side. If they need to run more wires, they'll drill more holes directly above the others. If a hole comes any closer than 1-1/4 in., your inspector will make you install a 1/16-in. thick protective metal plate (Fig. A). Available in 3-in. and longer lengths, the plates can be found at home centers and hardware stores.
The mechanical codes for plumbing and heating, ventilation and cooling (HVAC) systems also dictate that holes containing pipes be set back 1-1/4 in. from the edge of a stud to protect the pipes from fasteners. Those that come closer need to be covered by metal plates; for big pipes, use a long protective plate.
Electricians and plumbers spend lots of time drilling big holes, so they know a few tricks to make the job easier (or avoid it altogether).
Angled holes are tough to pull wires through because the cable catches on the sharp edges.
Holes square to the face of a stud are easy to pull wires through.
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
The best tool for drilling holes in studs is a right-angle drill with self-feeding bits.
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.