finding out foundation depth

AnotherJoe

bouicca21 wrote: »

My dad built an extension in the late 60s or possibly early 70s and I still remember him talking about being required to have 15 foot foundations for it (the rest of the house was 1930s and he thought the foundations would only have been 3 foot).

Hopefully you've missed a decimal point off there? Because no one would specify foundations 15 feet deep ! Thats getting into skyscraper territory. Unless you were building in a swamp or something. But then you'd use piles Id have thought,and if it needed that then the rest of the house woudl have subsided already.

bouicca21

Obviously a fantasy then. And such a prosaic fantasy. I must have missed out on the creatively imaginative gene.

lincroft1710

The odds are that it will not be deep enough. In the 1970s shallower foundations were allowed for single storey extensions than for 2 storey, but this is no longer the case.

John_Smith_2019

AnotherJoe wrote: »

Hopefully you've missed a decimal point off there? Because no one would specify foundations 15 feet deep ! Thats getting into skyscraper territory. Unless you were building in a swamp or something. But then you'd use piles Id have thought,and if it needed that then the rest of the house woudl have subsided already.

A few years ago a 4 storey pub was demolished and rebuilt from scratch as flats. I observed the builders using (what I assume are) piling foundations - driving 20 foot long pillars into the ground.

But I doubt the original pub building (or the others of the same height in the street) had such piling foundations, as they are all about 150 years old. They also all have cellars.
How structurally sound are these old 4 storey terraced town buildings? Because they are certainly common enough in the UK and I've never heard of any real problems (unless they are seriously neglected).

phill99

I've been in construction all of my working life and can assure you that 99% of domestic foundations are built to the minimum required for the extension in hand. So in this case, it is almost certain that the foundations would only support a single storey extension. Very few people think ahead and increase the specification of the foundations to allow for future first floor extensions.


However, some do. But as AdrianC suggests, physically digging the earth away around the foundations is the only thing thay will give you a definitive answer.


And for reference, the foundations have nothing to do with planning permission. Building Control have responsibility for the safe construction of properties.

stuart45

John_Smith_2019 wrote: »

A few years ago a 4 storey pub was demolished and rebuilt from scratch as flats. I observed the builders using (what I assume are) piling foundations - driving 20 foot long pillars into the ground.

But I doubt the original pub building (or the others of the same height in the street) had such piling foundations, as they are all about 150 years old. They also all have cellars.
How structurally sound are these old 4 storey terraced town buildings? Because they are certainly common enough in the UK and I've never heard of any real problems (unless they are seriously neglected).

They are usually pretty sound. They were built with lime mortar which allows for a certain amount of movement in the joints.
Depth of foundations depends on a number of factors such as type of subsoil, proximity of trees in clay soils, climate etc.

Tom99

As suggested above, the way to do it is to dig a trial pit or two.
I did this when putting a 4th bed on top of a single story kitchen.

Davesnave

Do the potential buyers know what minimum foundation depth would be acceptable to your council's building inspectors? If they don't, I'd suggest they find out first.

We have a mid-70s bungalow and our council required a minimum of 500mm existing in order to build up and make it into a chalet bungalow. That's not the same, I know, but there would be the potential to use pre-fabricated wood panel construction to lighten loading in your case as well.

We found the 500mm by digging 3 trial pits, but sadly that doesn't mean your 70s structure would be the same. Things were 'looser' in those days- just look at the fashions!

robatwork

elaneh wrote: »

hi all
can anyone help, I am being asked by a potential buyer how deep the foundations are of the extension of my Victorian house (kitchen and bathroom added at the back in a single story in the 1970s

You do realise you aren't under any obligation to answer anything other than "I don't know"?

Which is the correct response in this case. This really isn't your problem and don't make it yours. They won't pull out the purchase because you fail to give them a number in centimetres.

Waterlily24

Our bungalow had to be underpinned for us to do an upstairs extension. Don't know how old it is but probably 1920/30s.