I would expect to simply use 2 beams with a simple splice on the wall. Structurally they remain 2 beams. the splice just to locate them but up to your SE.
I take it the wall does goes down to ground?
I suspect yes.
PD assessment looks at the whole structure added to the original property so would probably take you way over 50% of the existing width when the garage is added to the new infill.
That's an important detail to omit!!
What does effectively mean though?
So best options: lift the beam so pipe goes under with say 50 clear or.. drop the beam so the pipe goes over again 50 clear. If neither is possible deepen the beam so your main steel has continuity and cover and maintains...
Is yours or public? If the latter you generally stop 150 clear either side woth your concrete and use a couple of PSC lintels over but to Water Co's requirements. If it's yours then just BC to satisfy so wrapping may be ok, but personally the reduction in volume of dig, muck away and concrete...
Go for it: SIP are an established name and Toolstation won't be selling rubbish. Have a look at Machinemart as a comparison.
I doubt you'll need 120A TBH. I generally run at 70-80A and I'm pretty sure they're 2.5mm rods which are fine for a wide range of jobs around the house.
Treat yourself...
You would be more likely to do multiple samples if there was a chance of finding asbestos. Where it's highly unlikely most peeps would just get on or you can send in a sample to confirm. So easy to get paranoid about the wretched stuff.
I don't think I've ever seen purlin supports at 1200 crs. Like any beam the loading (rafter length) and section (you'll find anything from 4x2 to 9x3) determines the length the beam can run between supports.
I would expect the props to come back to the central wall but you do need eyes on and...
Unless his quote specifically says arisings to remain on site I would view it as a cowboy chancing his arm.
Hand portable conveyors are another option for moving muck through a house. One assumes he has a plan for the concrete, bricks etc to go the other way?
Fair play to you for your plan and fair play also to the mum for not just plopping them down with the 'putor.
I had my grandmonsterskids (7 & 9) banging in nails prior to laminating a floor just a couple of weeks ago and they loved it. Agree with all FMT's comments and would add gardening...
It seems to me that if the heating chaps have cut through your dpm (the bitumen) and done nothing to reinstate it then the onus is squarely on them.
You might wind up at a state of equilibrium where the water leaking in was evapourated by the pipes and the floor stayed dry but I very much...