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Our floor joists are 2 X 8 s. The span is about 11 feet. Each joist is notched at the end so that the joist rests on a 2 X 4. That means the joist is only 3.75 inches wide at each end. There is no bearing wall above this area. I am wondering if it would be acceptable to extend the notch for another 10 plus inches at one end. I would like to put a 3 X 10 air vent in the space so that it is flush with the bottom of the joists. I could strengthen the joist by sistering 2 X 4s,or 3/4 plywood on each side, above the notch. Each sister would glued and screwed into the existing joist and would extend at least a 18 inches or so past the end of the notch. If I use plywood I could cut it so that it is the full 7 plus inches wide once it is past the notch. Do you think this will work or do you have any other ideas?
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If you choose to do this, the 3/4" plywood should extend beyond the notch and full depth of the joist as you mentioned. I wouldn't do it though without an engineer's okay.
Think about the day you sell the house and a buyer questions it and you find out it is insufficient. Now you have to make the correction or at least disclose the problem to all potential buyers.
I think the way it is now is insufficient and you either need a joist hanger on each one or the plywood solution to what is existing, even without a longer notch.
steve
*Hey Dan,No, I'd head off the joist instead.Ed.
*Are you talking about notching just ONE joist to accommodate the vent or every one to make the run of duct perpendicular to the joists?If it's every one - Forget it!! Or build another bearing wall inside the notched area and have at it.Single joist?? Ed. said header it, but where does the duct run come from?
*Got a technical question about all this for everyone.If I have a 2 x 10, and notch the end to fit onto a 2 x 4, would not my lumber now only be as strong as the thinnest, and weakest point - i.e. the notched end sitting on a 2 x 4 section? This qestion came up several years ago when I had to frame out a garage roof. The code for our area made me use 2 x 12's on 12" centers for the joists, but allowed 2 x 8's for the rafters. When we cut down the joists to meet the rafter line (at the top plate where they meet) it made the ends of the joists equal in width to the 2 x 8's. I brought this up to the Inspector, but he couldn't answer me. All he kept saying is "it's code". I was thinking then, and still think now that the wood is only as strong as it's thinnest and weakest section - i.e. the cutout section. Kinda the same thing for bird mouths on rafters, but I understand the load on rafters is not all downward whereas a joist load is (for the most part). Just a question...James DuHamel
*Thanks all.I'll take your advice and lose a few inches of headroom along the wall. Seemed like a plausible idea when I wrote it but seems like I'm pushing limits too much when I read it.Thanks again for the input.dan
*For James; an answer maybe.Doesn't it depend on the section properties of the member and the loads imposed at the PARTICULAR point in the span you want to analyze. So, near to the end of a span although the shear is usually higher, the moment is substantially less. 12" needed at midspan for moment, maybe 8" ok at support for shear. I'm not a PE, just remembering an earlier career. David
*I think David is right, the 'perfectly' engineered beam in terms of strength:weight won't be the same width across its center and its ends.C'mon, is there somebody who knows the details on this?GO
*The posts are correct. On a single, "simple" span, the bending moment (flexure) is largest at the center. The shear is greatest at the supports. Normally the section property requirements for bending provides more than enough shear capacity at the ends, so a couple of inches for an end notch is usually okay. Of course, following the electrician example, when in doubt, hire a professional.
*Another issue for those reading the thread is the increased likelihood of the lumber splitting along the grain at the inside corner of the notch.I see notched joists several times a year in older homes. There are usually a few that have split from the inside corner of the notch. I get the impression that they are more likely to split if that notch angle is 90 degrees, as opposed to >90, but I don't see enough to form a conclusion.As a general rule, the codes now don't allow notching for this reason.
*James ---The answer to your question is rather complex.The building codes give you engineering properties (E, Fb) of materials (various types of wood) that you can use to carry the specified loads (30-40 #/sqft in general less below roofs). You can notch and drill your wood to your heart's content as long as the engineering properties and design provide the support for carrying the load.The perscriptive code (not the actual engineering behind the code) forbids holes and notches because it is easier to ask an engineer to make the call than the building inspector.If your cutting of rafter ends was to the perscriptive code restrictions, then your rafters are fine.If the cutting was not to the perscriptive code restrictions, then your rafters may or may not meet the code. The answer depends on too many variables for me to even care about. Engineers get paid to do that work.The last two paragraphs apply to the original question also.
*You can notch a floor joist 1/4 the depth. (actual dim.) Any more than that you will have a problem with sheer.