Cutting an existing roof truss for an extension

Rather than trying to do all the modifications to the part of the truss that is left, I would suggest providing new rafters, sistered with the top chords, to span the kitchen. That way, the part of the truss that is left is just ceiling framing.

Have you tried modeling the truss if you just left the configuration as is and cut it at the wall and scabbed the web and the chords onto the wall stud. The spans looks pretty short and forces should be low so it might work just fine with a few nails.

If for some reason you need to keep the truss in place (I don't know the extent of the renovation, maybe the kitchen needs to be kept water tight), I agree with hokie66 - new rafters are much easier than modifying the truss.

If the renovation is extensive (kitchen being gutted and replaced) I would probably remove the entire truss and replace with new. Timber trusses are fairly cheap and easy to work with - by the time you shore up the existing truss and reinforce/rebuild in place, you may as well just buy new trusses. The new trusses will go in just as fast as you can reinforce the existing and then you don't have to work around half a roof truss while you build the new upper floor.

I've been involved in many renovations, and more often than not, trying to save a portion of the existing structure like this is more trouble than its worth.

I'm in the new truss camp. It will actually be faster than modifying the existing rafters. And from an economics standpoint, I'd be surprised if it wasn't cheaper even after considering the new ceiling drywall.

I like OP's original proposal. Minimal impact to roofing and ceiling and easy to install. Just as OP has done, I'd overkill the webbing to ensure that the chords and the web connections are lightly worked.

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.

Just to clarify my rafter proposal...I would take off the roof cladding to install the new rafters, then reinstate. I think Gousy is in Australia, so he would have either steel roofing or roof tiles, easy to reinstate. Ceiling with lighting, cabinetry, etc. not disturbed. I don't like the idea of installing trusses from inside.

You are going to have to take the roofing off to construct the upper floor anyway. Make sure the builder is equipped with the massive tarps which cover the whole roof. This type extension is common where I live. We did it to our house.