Hello,
My one-story house with crawl space has 26' long floor joists supported at midspan by a girder. Is there any reason not to to drill holes through the joists directly above the girder? I'm just wondering if the loading pattern over the girder is different than in the unsupported section. There is a 2x3 bearing wall above the girder that supports only ceiling joists.
Thanks, Wayne
You can drill reasonable sized holes in joists provided you place them on the centerline without significantly reducing the load bearing capability. It is best to keep them in the third of the span on each end.
Harry K
Depends on the size of the joists and size of the holes. One half-inch hole in the middle of a 10x2 joist is okay, and then only if the structure is sound.
Sorry, I guess my question wasn't clear. I'm familiar with the rules for drilling holes in joists through an unsupported portion of the span. My question is just whether there is any special consideration with regard to drilling a hole directly over a support, e.g. a girder with a bearing wall above.
Thanks, Wayne
How big of a hole are you asking about and what sort of joists are they?
R
I'm talking about a 3/4" hole for plumbing supply line in a 2" x 9.5" No 2 DF joist. I know that's no problem in the outer third of an unsupported span. I'm just wondering if there are different rules for a hole in a joist directly above a support and below a bearing wall, since I imagine the usual loading (top half of a joist in compression, the bottom half in tension) would not apply.
Thanks, Wayne
The force immediately adjacent to the bearing point is entirely shear, so a hole that small wouldn't matter for your one story house. I'd be reticent about locating it there for other reasons, but probably not a problem.
How old is the house that you have 26' long dimensional joists?
R
When you say shear, is that the same as compression perpendicular to the grain? I would think this would apply over the entire bearing surface, not just at the boundary of the bearing surface.
Could you explain? I can locate them anywhere I want, I just thought that over the girder would be out of the way. Would a 3/4" hole along the neutral axis of the unsupported portion of the joist be better (strength-wise) than a 3/4" hole over the bearing surface?
1908. Too bad the joists are No 2 or No 3, there are some knots, knot holes and splits. Perhaps I should closely check the middle parts of the unsupported spans for such defects and apply gussets where needed. I did sister (without jacking) the two joists under the cast iron bathtub sitting at midspan and running parallel to the joists, the sag of the old 9.5" deep joists was only about 1/4" at midspan, judging from the fact that the new 9.25" deep joists were tight to the supports at the girder and exterior wall and tight to the subfloor at midspan.Cheers, Wayne
Draw 45 degree lines up and out from the top of the girder to the top of the joist, and down and out from approx. where the wall above is. You should in, theory not drill there, without adding blocking first, because that section is under compressive loads. In practice, a 1/2" hole is unlikely to matter much. OTOH, just getting a drill IN there is going to be a pain in the ass. My drill with a
1/2" spade bit in it is more than 14.5" long.
How do you plan to get 10' lengths of piping in there? If the wall above is 2x3s, why do you think it's load-bearing?
I only need a 1/2" pipe, so I'm going to use soft copper (5/8" tube). I was pleasantly surprised to find out that locally it is only 20% more expensive than hard copper type L ($1.20/ft for soft copper, $1.00/ft for hard copper).
Because it supports the 26' 2x6 ceiling joists at midspan? This is
1908 construction.Cheers, Wayne
Good, that's the sort of answer I was looking for, thank you. I ended up drilling 12" and 15" away from the edge of the girder at the midline of the 9.5" deep joists. So I should be clear. The bearing wall is roughly above the girder or slightly offset to the other side.
I'm using a 3/4" hole for 5/8" OD tubing.
I have a right-angle chuck (from Harbor Freight) that is invaluable in this situation. Still a pain with all the wood chips raining down.
Cheers, Wayne
You should have no problem drilling a hole in a joist at that location, of course a lot depends on the size of the hole. If you have any doubts, you could always nail an additional piece of 2x6 to provide some additional support, but I really don't think that it is necessary in most cases.
A 2x6 in compression, even with a 1" hole in it is a formidable component.
I'll bite. Why don't you just move it away from the midpoint a ways, and then come back again when you get where you're going?
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I would suggest you consider PEX tubing for your fresh water re-pipe. I've done the soft copper thing & it sure does start out soft but work hardens in short order (esp with me on the throttle). I'm done with copper (even though that's all I even used) PEX is the way to go. I'm facing a re-pipe in my current house (1930) , original galvanized steel still in service in some places!
cheers Bob
Not if the member is continuous across the bearing point. You can get significant bending stresses in that case.
Mike
Good catch! I screwed up on that one. The bending moment is indeed greatest over the central bearing point. Thanks.
R
Unfortunately, PEX is not approved for use in California.
I was surprised that the soft copper is harder to work with than I imagined. I just want to get a 16' length through 12 joists. The best solution I've come up with so far is to run a rope through the holes in the joists, tie a knot in the end, feed the knot into the soft copper, crimp of the end of the copper down to capture the knot, and pull on the rope with a come-a-long. Still a serious pain.
Cheers, Wayne
Sure, I could do that, and in fact I ended up doing that. The question was whether there is any reason to do that.
Thanks, Wayne
Aha.
(I'm glad I asked)
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