conceptual: RSJ in foundation

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In 90% of cases in domestic work, you don't actually need a goalpost frame, even when taking out the whole of the rear wall. There is usually enough residual stiffness in the existing walls of the house to maintain stability.
Problem is, it's time-consuming to prove the adequacy of the walls as shear walls, so most SEs find it less hassle to specify a frame.
 
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that's true, but...

when the whole wall is taken out, there's no wall return to rest a top beam on, so that option is void. without that, the next "best" option is a goalpost, but this comes with increased costs: pouring a pad foundation for it. it's easier to go for a beam in the ground, though it's probably overkill.
 
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that's true, but...

when the whole wall is taken out, there's no wall return to rest a top beam on, so that option is void. without that, the next "best" option is a goalpost, but this comes with increased costs: pouring a pad foundation for it. it's easier to go for a beam in the ground, though it's probably overkill.
If you are opening to an extension, you put a spreader in at right-angles to the beam so that the reaction from the beam is suitably dispersed, as it would be with a normal padstone; you don't need a projecting pier to support the beam.

We usually use cut-down 6" x 4" or 9" x 4" reinforced concrete lintels to make the spreader.

If your extension has reasonable return walls, and the roof structure is well-tied to the surrounding walls that - along with any other walls at ground floor level - usually suffices to make the structure robust.
 
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What it means to be in business and have experience :).

I’ll stick to the box frame for now, I’ve changed some details once already, but good to know for any future projects.

Thanks all for your help!
 
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I’ll stick to the box frame for now, I
Very sensible at this stage as you will have their insurance behind you.
And as you and R.R. have noted, it's often cheaper/easier to drop a ground beam in than form separate pads for columns.
 
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I also like to overdo things. Why not have a structure that can hold 3 extra floors to hold a roof made of 5 wooden joists and a layer of fibreglass?

You never know when you need more… Kilo Newtons :).
 

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