Clearing ground for extension plus hardcore needed for it

[spada01]

Two questions. I'm going to extend my house at the back next year

1. There's currently a 4 inch concrete base where the extension will go. I presume the extension ground works wont be able to incorporate this and it needs clearing so there's just a soil site?

2. I'm also taking out an entire chimney and stack. Will the bricks from this or the lumps of concrete from a path outside be useful for hardcore for the extension or will smaller or different hardcore be needed?

 

[noseall]

1. There's currently a 4 inch concrete base where the extension will go. I presume the extension ground works wont be able to incorporate this and it needs clearing so there's just a soil site?

Correct. The 'oversite' preparation usually needs digging down in excess of 400mm below dpc.

2. I'm also taking out an entire chimney and stack. Will the bricks from this or the lumps of concrete from a path outside be useful for hardcore for the extension or will smaller or different hardcore be needed?

Depends. If the extension oversite is on a slope or there is a large amount of contaminated back-fill to remove, then these deep areas can be filled with large lumps of hard core.

However, if the oversite is only asking for say 100mm of fill then mot type1 stone is the most suitable.

 

[RedHerring2]

1. There's currently a 4 inch concrete base where the extension will go. I presume the extension ground works wont be able to incorporate this and it needs clearing so there's just a soil site?

Correct. The 'oversite' preparation usually needs digging down in excess of 400mm below dpc.

There might be the odd exception, Noseall.
I have a 3 metre X 3metre (about 100mm thick) slab of concrete outside where the extension is going. The BCO asked what I intended to do with it. I told him I'd break it up but leave it there. He said to not bother breaking it up, just leave it there. He reckoned, if I shifted it I'd probably have to clear a bit deeper.
Mind you, the top of it is about 500mm below dpc, so it's already below your 400mm so there's more to go on top of it yet.

2. I'm also taking out an entire chimney and stack. Will the bricks from this or the lumps of concrete from a path outside be useful for hardcore for the extension or will smaller or different hardcore be needed?

Depends. If the extension oversite is on a slope or there is a large amount of contaminated back-fill to remove, then these deep areas can be filled with large lumps of hard core.

However, if the oversite is only asking for say 100mm of fill then mot type1 stone is the most suitable.

It still needs whacking about every 150mm, doesn't it?