Timber Frame foundation

[robinbanks]

Are you going through Building Control?

And how much do you have to bribe a BCO to let you use a surface patio slab as a foundation?

 

[Notch7]

Correct

OK, so it is a house extension, a habitable space.

It will therefore be subject to building control and you will need foundations which will be the same whether timber frame or brick / block

and the floor will need to be either solid concrete slab or suspended floor

 

[noseall]

Do I need any foundation, if I do, how deep?

You will require a standard foundation. Dig down to load bearing strata - usually in the realms of 1m deep, but can be shallower as long as the dark matter growing soil has changed to virgin earth - which is usually indicative of a distinct colour change, i.e. sandy, stony or clay substrate. This needs to be showing that it is unlikely to change at depth.
Width of foundations will depend upon how you design your walls above.

 

[stuart45]

London clay might be an issue if there's trees close by.

 

[noseall]

London clay might be an issue if there's trees close by.

Or a thirsty hedge.

Good point though. I'm sure his designer will point it out.

 

[firapara]

Are you going through Building Control?

Yes, no planning application, just building control

 

[stuart45]

You are governed by your BCO for the foundations then. Have a look at Durabase modular foundation bases for lightweight structures.