Reinforcing existing wood joist

[lexpatrie]

I have a 15' span 2x10 from 1930s. There's been a roof opening cut to accomodate an HVAC duct, 30" x 30". The joists are 16" o.c. with wood plank substrate on the top side. This opening has cut two joists each side of the opening and is now supported by face mount hangers with new framing (header joist) to support the cut joists. The main 15' 2x10 joist takes uniform load from the roof, and concentrated loads at the header, so I'm curious the attachment strategy if there's a need for a second 15' joist (it goes on the far side of the header, of course), discrete fasteners or distributed?

Only overstress currently is bending. I could get fancy with the bending stress for older wood, but the overstress is large enough I don't think it will pan out.

Would you all potentially design a connection between the two 2x10 plies (one existing, one new) for the (point) load from the header alone? Since the HVAC is "permanent" I'd go with a duration of load of 1.0 for the unit alone and 1.15 when I add the snow. Roof live isn't a controlling case.

(It's not light gauge, this is just the one fairly decent drawing I could find).

 

[phamENG]

I'd do both point and continuous inter-ply fastening. For only cutting two joists, it would probably be enough to have them use longer nails/screws in the joist hanger to catch both plies. If it's already in place, I'd just add enough fasteners on both sides of the connection to ensure the point load is shared. Then code minimum distributed fasteners for a multi-ply wood beam.