holes in wood joists
holes in wood joists
(OP)
The electrician drilled 3 3/4" holes an inch or so apart through a series of 2x10 joists. There is about 1-1/2" from the bottom of the holes to the bottom of the joist. There is more than one set of three holes and the distance from the end of the joists varies but they all appear to be in the middle third of the length of the joists. How about a 10 gage strap 1.5" x 18" or so screwed to each side of the joist under the holes. This is a house. 2x10 are at 16" oc and span 15 ft





RE: holes in wood joists
I usually try to restrict the hole size to no more than 1/3 the depth of the joist (3" here), centered on the centerline of the joist, and in the middle third of the span for shear. You need to check the S value at each hole and the associated moment for that location. Shear is mopre than likely not an issue, unless it is a transfer beam.
I don't like what this guy did - he should know better. If I had my druthers, the joists would be sistered with new ones, and properly re-drilled under your direct supervision. But, I'm not the engineer.
Bottom line is don't try to patch the situation with a gerry-rigged fix. Do it right if possible.
Mike McCann
MMC Engineering
RE: holes in wood joists
I agree though, patch it right.
RE: holes in wood joists
Mike McCann
MMC Engineering
RE: holes in wood joists
Mike McCann
MMC Engineering
RE: holes in wood joists
the consensus is "forget it".
Thanks guys
J
RE: holes in wood joists
RE: holes in wood joists
First, 2x10 joists at 16"o.c. for a span of 15ft is pushing the limit for 40psf LL/ 10psf DL.
Second, the diameter of the holes may be acceptable, but the location is in the bottom 1/3 of the depth and the holes are spaced too close. This is against code. Are you comfortable accepting a code violation?
I would reinforce the joists with OSB, LVL lumber or metal strapping. I have liked the performance using OSB glued and nailed to one or maybe each side.
Lastly, this electrician should not get away with this. He's just going to keep doing it until he has to start paying for his mistakes.
Jim Houlette PE
Web: www.evstudio.us
Online Magazine: www.evstudio.info
RE: holes in wood joists
Scott
www.dbssinc.com
RE: holes in wood joists
personally I think your strap idea should be adequate.
But what I would do is to calculate the stress on the section allowing for a stress concentration of 2 at the holes and then if that is less than allowable then I would accept it. 3/4" holes get put in joists all the time without the engineer knowing about it.
RE: holes in wood joists
RE: holes in wood joists
The IBC specifies where and how large holes and notches can be in a joist.
RE: holes in wood joists
RE: holes in wood joists
I agree with RVSWA. Straps with nails will slip and when I previously mentioned the joists are already poorly designed for the span.
If it was one joist and the span was shorter, I would consider a strap. But this is a series of joists. You will have one angry homeowner and I predict if straps are used, you will be dealing with this later, and paying for the repair.
Jim Houlette PE
Web: www.evstudio.us
Online Magazine: www.evstudio.info
RE: holes in wood joists
Thanks
RE: holes in wood joists
I typically recommend a structural glue that is epoxy based and has a wood lap shear strength of at least 1,500psi. But I have also allowed typical 'liquid nail' glue that may not meet the needed ASTM requirements for true structural glue. Just depends on the repair needed.
Jim Houlette PE
Web: www.evstudio.us
Online Magazine: www.evstudio.info
RE: holes in wood joists
RE: holes in wood joists
Adding plywood or OSB to the bottom of the joists would give you the strength needed if designed correctly (composite action with the needed connection between materials to act together). I've had a builder do this and it really made for a strong floor, you can then think of it as a SIP (structural insulated panel) floor system.
Jim Houlette PE
Web: www.evstudio.us
Online Magazine: www.evstudio.info