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How big of a hole Can I drill in a 2x6 floor joist?

For anything else, you're allowed to notch 1/6 of the joist depth deep, and 1/3 of the joist depth wide. Here are the maximum numbers for some common sizes: 2×6 (5-1/2″) ~7/8″ deep, 1-13/16″ wide.

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Every carpenter, electrician, plumber, HVAC contractor, and home inspector should know the rules for allowable cuts and holes into floor joists. Cuts and holes are known in the trades as notching and boring, respectively. The rules for notching and boring come from section 502.8 of the International Residential Code, which addresses cutting, drilling, and notching. Today I’m only focused on traditional dimensional lumber, like 2x8s or 2x12s. I’ll discuss holes in manufactured floor joists, aka I-joists, in next week’s blog post.

Rules for boring/drilling holes

To start, here’s the diagram that comes right out of the codebook.

You can put holes in floor joists anywhere along the length of the joist, but you can’t put them any closer than 2″ from the top or bottom edge of a joist. The maximum size of a hole is 1/3 the depth of the floor joist. Dimensional lumber will always be a little smaller than the stated dimension unless you’re dealing with some ancient lumber. For example, a 2×4 actually measures 1-1/2″ x 3-1/2″. For floor joists, here are the maximum hole sizes for common floor joist sizes:

2×6 (5-1/2″) ~ 1-13/16″

2×8 (7-1/4″) ~ 2-3/8″

2×10 (9-1/4″) ~ 3-1/16″

2×12 (11-1/4″) = 3-3/4″

If you’re dealing with rafters, these same rules apply.

Rules for notching

The codebook has two diagrams for notching; one at the ends of the joist, and another for notching anywhere else. Let’s start with the easier one, notching at the ends. You’re allowed to notch 1/4 of the joist depth at the end of a joist. For some common sizes, here are the maximum notches allowed:

2×6 (5-1/2″) = 1-3/8″

2×8 (7-1/4″) = 1-13/16″

2×10 (9-1/4″) = 2-5/16″

2×12 (11-1/4″) = 2-13/16″

For anywhere other than the ends, we use a different diagram.

You’re not allowed to do any notches in the middle third of a floor joist span, and you’re not allowed to notch the bottom side of members over 4″ in nominal thickness. For anything else, you’re allowed to notch 1/6 of the joist depth deep, and 1/3 of the joist depth wide. Here are the maximum numbers for some common sizes:

2×6 (5-1/2″) ~ 7/8″ deep, 1-13/16″ wide

2×8 (7-1/4″) ~ 1-3/16 deep, 2-3/8″ wide

2×10 (9-1/4″) ~ 1-1/2″ deep, 3-1/16″ wide

2×12 (11-1/4″) = 1-7/8″ deep, 3-3/4″ wide

Summary

When any of these rules are violated, it’s a judgment call. When these rules a fudged just a little bit, I usually don’t make a big deal about it, especially if it looks like it has been that way for a long time. These numbers always assume the maximum loading for a floor, along with the maximum spacing of a floor joist. But when these rules are egregiously broken, that’s when it’s time to call in a carpenter for repairs. And note, I didn’t say to call in an engineer for further evaluation. This is basic floor framing, and any qualified carpenter ought to be able to make repairs without having to do a bunch of difficult math. And just for fun, here are a few classics we’ve found over the years.

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Can I build a shed floor with 2x4?

I have a shed built completely with 2x4s: studs, mud sills, top plates, and rafters. Of course, the "skin" is plywood and siding. For a shed you're generally okay with 24" centers, rather than 16". For your floor, since you're not using a concrete slab, you will probably want 16" centers.

diy.stackexchange.com - How much of a shed can be framed using 2x4 lumber?

The place I work at has been ordering new machinery and it comes in with 2x4 frames. They are throwing the wood away! Anyhow, I can get all I want. So my question is how much of the shed can I do using only 2x4's? I see most bases of the shed are done with 2x8's or something along that line. I will be building it off the ground with blocks as I cannot afford a concrete slab at the moment. I would like to build more of a shop than a shed. Maybe 15x20? But my longest "free" wood is 12 ft. My current shed is a dirt floor. I could live with that if need be. My current shed is old school. I live in the country, so no certain requirements have to be met. Anyhow, the sheds bones are old utility poles. It's in an awkward spot, so I wanted to build a newer one in a different spot. The walls are tin. No plywood on the walls. Roof is tin as well. I'm just trying to see if the wood I get at work will be enough to cover 90% of the cost. I want 20ft long, so can I build 2 ten ft walls and join them together to make 20ft? I understand that may not be proper, but it's a shed not a house.