How deep are my foundations?

[Cotswold Jim]

I appreciate this is a question without a definitive answer, unless I dig an inspection pit. as I know there are many factors to consider which will determine this. But if people have any general ideas of the likely approximate answer I would be interested to know.
I’ll give a bit of background, which will hopefully make my question make more sense.

I live in a 1937 Semi, fairly typical of most 1930’s semis, solid brick walls, bay windows, hip roof etc.

Later this year we plan to build an extension which will include a single-story garden room to the rear.
It’s this single-story extension is the bit I’m unsure about, I’m not sure if I need to give party wall notice or not.

We are not physically touching the party wall, but looking at the party wall Act guidelines, we need to give party wall notice if we excavate within 3m of a party wall, where we did deeper than the original foundations.
Our architect/structural engineer plans specify that the new foundations for our rear extension need to be 1m deep (subject to building control approval) therefore if the original house foundations are 1m or deeper then I don’t need to give notice. If they are likely to be less than 1m, I guess I should give notice.

Ordinarily I would just give notice to be on the safe side, but our neighbour, who we get on with quite well is an older lady (late 70’s – early 80’s) who lives on her own and is a bit of a worrier. Although we get on well, she isn’t overly keen on our extension although being very polite about it.

I know if I do serve party wall notice on her, two things will happen
1) She will worry about it all and probably cause her undue stress.
2) She is likely to just ignore it. Then a dispute is deemed to have arisen. This is what I really want to avoid as this will just be a whole world of pain where we must appoint “agreed surveyors” and such with the costs that incurs.

So, if, in all probability, the original foundations are 1m or deeper, then I don’t need to go down this road at all.

Just to be clear I’m not trying to avoid doing things properly, and in the very very unlikely event of our works causing problems, then there is no question of us not putting everything right.

[Equus]

Cotswold Jim said:

...this is a question without a definitive answer, unless I dig an inspection pit

Ding!

It will probably take you about 20 minutes with a shovel to expose the foundations, so extract your thumb from your arse and stop speculating.

As a general rule, however, foundations on older properties tend to be shallower than on modern ones, unless there is a cellar (people didn't tend to understand frost heave or clay heave due to root action back then: once they were through topsoil, that was frequently judged to be 'good enough'), so there would need to have been a good reason for them to have gone down to a metre. The first proper, nation-wide Building Regulations weren't introduced until 1965, so before that, control of construction quality was patchy at best.

[Cotswold Jim]

ahh thanks, that is what I was worried people might say.

although a relatively fit, active and hands on person, I dug a soak-away last year and it was bloody hard work so I'm slightly adverse to digging at the moment :-)

But as you say I probably need to get over myself and pull my finger out :-) Thanks for the reply

[magooagain]

You can dig down the side of a corner of the house to get an idea what the foundations are.

Given the age of the house I would bet below soil level on about 3 or 4 courses of brick and about 12 to 18 inches of concrete.