Are 600mm foundations wide enough for 2nd storey?

[MummaB2016]

So we've moved into a house that has a single storey extension on the back. We want to go over it to make it 2 storey and are trying to determine if the foundations are suitable before we start paying for architects and the like.

I understand that the width of foundations is important here. Ours are 600mm. Can anyone advise if generally this is wide enough to support the 2nd storey? The depth is 1m which we think is fine but the width is what we are struggling to determine in our research so far.

We will have building control out to have a look too but as we've dug a hole on a Saturday we can't get hold of them today and are impatient :)

Any advice/thoughts would be appreciated! Thanks

Yes should be fine. We are just having a double storey on clay, and the width is 600 based on the allowable bearing pressure for clay, and the depth is 1m based on the movement of the soil itself.

Although having said that the existing house is 2 storey, once they started digging they found the existing house is just brick footings directly on the ground! Been like that nearly 100 years no problem!

A good indicator is the age.

Older houses, bungalows and extentions may have very meagre foundations. Since about the 1980's, you have been required to use a foundation which - even for a bungalow - is enough for an extra storey to be built on top.

Foundations are also deeper because they are required to be below the influence of factors such as ground frost. it's a bit more scientific now because the load-bearing ability of the ground is assessed (lots of homes are built on re-used land that may have been filled or made-up).

You don't see so many of the Victorian jerry-built homes with inadequate footings because a lot of them have fallen down, especially during WW2 bombing of towns and cities.

Thanks for your comments. The house is 40s built but we want to go over an extension that was built in 2003 so I'm feeling pretty confident that we'll be ok... next step - finalise plans and get in structural engineer!

try to look up the 2003 BR plans, they are likely to be accessible on the local council's website.

I think you'll find that you can build a structure up and around existing one storey if foundations weren't deep enough (pigletjohn?).

Yeah we've got the plans but not enough details re foundations.

Good news though, structural engineer says we are good to go!