How to tell what foundations my house has?

wilco88 · 15 Jan 2021

Hi,

I am planning on doing some drawings for building regs purposes. Some of the foundations of the house are visible as we have removed floor boards and had a dig around. Without digging right down, it's hard to make an accurate drawing. Any tips for this?

And......how would an architect or struct eng tell what foundations a house has without such access or without digging?

Thanks!

johnny2007 · 15 Jan 2021

Why would you need to know?
Unless you dig, you can never be sure.

wilco88 · 15 Jan 2021

I just want to show the foundations accurately on my building reg drawings.

Mottie · 15 Jan 2021

Better get the spade out then.

wilco88 · 15 Jan 2021

"..how would an architect or struct eng tell what foundations a house has without such access or without digging?"

Mottie · 15 Jan 2021

wilco88 · 15 Jan 2021

funny.....not useful.....but funny

^woody^ · 15 Jan 2021

wilco88 · 15 Jan 2021

Please tell me you took the time to draw that!

^woody^ · 15 Jan 2021

It's my business card

^woody^ · 15 Jan 2021

Why do you need to show existing foundations?

Just draw a nominal rectangle or stepped flooring for older houses going down to 750mm or thereabouts.

If trial holes are needed just anote that on the drawing.

wessex101 · 15 Jan 2021

There are far too many variables so most people just make an educated guess based on age of the property, local ground conditions etc. The usual annotation you see on drawings is "foundation depth to Building Inspector's approval"
If you know you are on clay and it is a post 1976 house you could reasonably assume the foundation will be at least 1 metre deep. If the house is older the foundations are probably shallower. However, unless you have a very specific reason like a heavily loaded pad foundation or concentrated point load a trial hole is rarely needed.
If the existing house has special foundations such as piles or a raft that would be useful to know in advance although very difficult to check that if you don't already know. Usually it is a well known fact locally where housing estates were built on bad ground and needed special foundations not so easy if it is a one off house or small development.
It is often one of those things that until you start digging out the foundation trench you don't know what you will find.

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How to tell what foundations my house has?

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