Notched Wood Beam @ Roof 2

[dursunlutfu]

Hi Folks,

I was just wondering if any of you guys analyzed a notched wood beam by considering the notched section as a cantilevered beam. I have 2x12s at the roof framing and because of architectural reasons, I am cantilevering the notched 3 feet portion of 2x12s. It is basically a 2x12 spanning between two walls and cantilevered out 3 feet (notched to 2x6) from one of the walls. Do you guys agree with the cantilevered beam analysis approach for the notched part of 2x12 ?

Thank you so much for your time.

 

[CANPRO]

Is the full depth of your 2x12 bearing on the wall or the notched portion? If the full depth is bearing, and the reduced section cantilevering, then you shouldn't have an issues. If your reduced section is bearing on the wall, I'd be surprised if you have enough shear capacity left.

The way you phrased your question, I suspect the notched section is bearing on the wall. A sketch would be helpful.

 

[XR250]

I agree with CANPRO. If it is notched at the interior face of the wall, sometimes you can add joist hangers to compensate.

 

[KootK]

I doubt you'd see any trouble but, just in case...

I'd rather do a single long screw from the top but, given the proportions, I'm not sure that would be practical.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[EngineeringEric]

My not backspan with 2x6 1.5x cantilever? more material, far less labor and risk of over-notching?

 

[KootK]

I change my answer to Eric's. That would be cheaper and better I think.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CANPRO]

Agreed that Eric has the best solution if the notch is as shown in KootK's sketch. I think his solution is even better than he gives himself credit for - I'd say its actually less material (or cheaper material anyway) if you can get away with buying a 2x12 that is 3' shorter.

 

[charliealphabravo]

Of course you wouldn't typically want a notch right where the bending stress is highest. For example you wouldn't typically allow a notch on the underside of the main span except at bearing where bending stresses are negligible. At bearing, an underside notch up to a depth of D/4 would typically be allowable.

But of course we install D/4 bird mouths at rafter bearing to form eave overhangs. Typical eave overhangs are 12/16/24 inches. A 36-inch overhang is pretty aggressive.

My thinking is that if you want to notch greater than D/4 to create the cantilever then you might want a larger main member or use a sistered 2x or some formal reinforcement of the joint.

Edit:
I think a notch past D/2 looks bad and should be reinforced. I like KootK's detail. I might suggest rather using 3/4" plywood each side and wood screws for the full capacity of the uplift so that you are basically replacing the full thickness of the main member and have a stiffer/stronger connection. Common nailed 2x to 2x connections take a bit hit on capacity/stiffness, especially when the number of fasteners is low and you have rotation.

 

[msquared48]

You will just have a staggered plywood seam at the edge of the wall, but that is no big deal.

Mike McCann, PE, SE (WA)

 

[dik]

and PL Premium adhesive...

Dik

 

[dursunlutfu]

Thank you all for your responses. Regarding the option that Eric suggested, it is not really more feasible than notching because if I use cantilevered 2x6s, I will end up using 2x6 s under the cantilevered 2x6 beams to attach the ceiling.
Regarding over-stressing the notched section, I can not grasp why the notched section will over-stress the 2x12 when it is bearing on the wall. According to my understanding, having a cantilevered 2x6 will act in the same way as notched 2x12.

 

[CANPRO]

It’s not clear to me what your framing looks like. Why the additional 2x6? Can you post a sketch of your proposed detail?

My understanding is that Eric was suggesting you scab a piece of 2x6 on the side of the 2x12 and let the 2x6 cantilever 3’.

 

[dursunlutfu]

@CANPRO here is the sketch.

 

[kmart30]

I would use a scab not a notch. Reason is its easier for the framer to understand and it leaves less room for error. What if he notches it 4 inches instead of 6 and he notches it too far? You would have to draw a specific detail showing everything so its clear when you could just use a note and callout to make it clear. Just my opinion....most framers around here dont even read plans because they all have been doing it for 30 years and know everything.

 

[dhengr]

Dursunlutfu:
I would use a sistered 2x6 for the 4’ canti. with a proper backspan. I would stand a 2x4 x 5.75”+/- high block under the 2x6 in line with the wall below, as bearing blocking. Cutting that canti. out of a 2x12 is expensive. 4’ of 2x12 is pretty expensive, per board foot, on a longer 2x12 in a high grade of lumber. Then cutting out the bottom portion, 4’ x 5.75”, needs layout and marking, circle saw time, and clean-up hand saw time (or jig-saw time). The corner is invariably over sawn in both directions unless you stand right there and watch them.

 

[dursunlutfu]

Thank you all for valuable answers. I will sister 2x12s with 2x6 to cantilever it out.
It looks like that will be the best option for the ease of construction.

 

[Tmoose]

Does your sketch indicate the cantilever could be 4'-0" ?