Large Notch at Rafter End

[STrctPono]

I'm helping out a friend on their house design and I'm going out tomorrow for an inspection. He sent me some progress photos and I noticed that the carpenters notched the end of the rafters significantly! It looks to be about half the rafter height. They are 2x12 rafters. I checked it and the capacity is now well under the demand. What are some options? Do they make any inverted sloped rafter hangers that can be nailed to the double top plate? How about strengthening the notch with some steel plates screwed/bolted in from each side? I appreciate any advice.

Thanks

 

[Greenalleycat]

That looks like shit. But if I've learned anything about residential structures it's that looking like shit does not preclude something last 100 years or more
Notch calculations give you fuck all capacity and nothing works, but I've also seen some truly heinous construction last a very long time without any manifestation of an issue
(not to be construed as a professional engineering opinion)

I'd check the drawings first and see what detail was shown (not sure if these are 'your' rafters or the architects) as it's good to know where you sit with regards to the contract before you go in all guns blazing

A non-numerical solution is to get them to drill a round hole next to the notch so that the crack can't propogate
Then drill a long screw up to stabilise any crack that does form

You could also get additional blocking installed then use a shear connector that connects beyond the starting point of the notch
There is still the risk that shrinkage causes the crack to propagate though
No idea what you 'muricans would call them but this is what we would use

https://miteknz.co.nz/products/nailon-fixings/mg/

 

[Eng16080]

That's a lousy picture, but I think I get the gist that this was built like crap.

Some options:
[ol ]
[li]Plywood gusset plate on one or both sides to minimize the splitting risk at the notch location.[/li]
[li]Maybe there's a shallow top mount hanger that could work assuming you cut the bottom of the rafter flat at the hanger seat, like a Simpson HUTF24, for example.[/li]
[li]Add a continuous wood ledger directly below the rafters which is fastened to each wall stud.[/li]
[/ol]

I wonder if the header beams in that wall are adequate.

 

[XR250]

If you flatten the rafter out at the notch (level cut), is it still considered a notch?

 

[phamENG]

Gross.

I agree with Greenalleycat on the correction - run a long screw up through the joist to resist splitting or use a steel strap on the side of each joist. I seriously doubt you'll get sufficient shear capacity out of the notch, but you could certainly try. The equation is the NDS - section 3.4.3 (at least that's where it is in the 2015 version).

 

[XR250]

Have you checked the shear with the actual height? From NDS, "A gradual change in cross section compared with a square notch decreases the actual shear stress parallel to grain nearly to that computed for an unnotched bending member with a depth of dn"
That's what my comment about flattening out the rafter was about.

 

[STrctPono]

Thank you all for the responses. Sorry for the bad photo. It was all that was sent to me. This is my design but I showed the rafters at full bearing on the double top plate and notched only for the extension of the rafter into the eave overhang. The house has a transition from rafters/ridge beam to prefab trusses. I'm guessing they did this because the carpenters didn't want to do a wall height transition to account for the difference in height from the rafter to truss top chord. This is annoying.

Shear was checked with the notch height. Judging from the photo, it appears to be about half way. Shear demand is 704 lbs and shear capacity has been reduced to 183 lbs per rafter based on NDS equation for notched members.

That's an interesting section regarding flattening out the notch. If I do that, the shear capacity comes out to 731 lbs..... Seems almost too good to be true. See attached picture. Is this your interpretation of NDS?

If I utilized the vertical screw approach, I would probably want to do this in combination with the added wood ledger for a belt and suspenders approach.

The added steel side hanger is a tempting option. I need to find an option for this here locally. I feel like I've seen something similar that Simpson Strong Tie makes....

Lots of good ideas to consider

 

[XR250]

That's an interesting section regarding flattening out the notch. If I do that, the shear capacity comes out to 731 lbs..... Seems almost too good to be true. See attached picture. Is this your interpretation of NDS?

Yup. Does seem like a free lunch.

 

[Greenalleycat]

Just tell the contractor that they haven't built it as per the plans and you're going to sue them if they don't redo it properly

Works every time

 

[XR250]

Just tell the contractor that they haven't built it as per the plans and you're going to sue them if they don't redo it properly

That seems a bit harsh.
Mental note: Don't do any work for GreenAlleyCat!

 

[Greenalleycat]

I'm kidding, I'm really tough on internet forums but am actually a big softie in the flesh
Literally and metaphorically, all this hard work really takes a toll on the physical fitness....

But the main point is that OP's mate shouldn't be paying for the remediation here - the contractor hasn't followed the plans