Boring through joists

[tarajjones]

I'm converting a room into a laundry room and after I gutted it I found a 2 inch drain line behind a sofit. I would like to remove the sofit but I would have to reroute the drain line to do it. It currently is running along the bottom of (5) 9"x2" wood joists. Can I drill 2 1/2" holes through the center of these joists and rerout it and still be in code? It would be a little tricky since I would need to have it run down hill to keep it draining, but I think I can manage doing that.

[jproffer]

It would be a little tricky since I would need to have it run down hill to keep it draining, but I think I can manage doing that.

I don't think you could keep all the holes in the center of the joists and still get the drainage required. 5 joists, at best (16" centers) covers a little under 7 feet, so over the length of the run you would have to drop 1 3/4" to keep 1/4" per foot drainage. If the joists are 9" tall, you would have to start 7/8" above center and drop to 7/8" below center (hole centerline), which would only leave 2 3/8" above (and below) the first (and last) holes, respectively. Even that is only if you can get the startoing point perfectly in the right place. For this reason I would say it's a no go. I'm not sure about codes in your area, and I'm not even completely sure what percentage of a joist can be bored, and how much has to remain above and below the hole, but I wouldn't do it.

[Sweep]

Most building codes spell out what penetrations are allowed in joists. I can't help without knowing where you live or what code applies.

[Don_P]

The ICC code says 1/3 the depth maximum, no closer than 2" from either edge.

Lumber grading views knots the same as holes for the most part. One basic rule of thumb for knot displacement when grading is "quarter,third,half". A No.2 stick of wood has no knots or holes occupying more than 1/3 of its cross section anywhere along its length (ok, supposedly). If you look at design values for wood, they drop by about 1/4,1/3,1/2 as the grade drops from No1 to 2 and then 3

The way I interpret that is that when you do drill a d/3 hole you are limiting it to being no worse than a No.2 defect.

I agree that your local rules apply. I was just rambling on about the why as I understand it.