Raft foundation - close to existing structures

[WisteriaMews]

Does anyone know with a raft foundation how close you can get to existing structures?

 

We have an existing sewer connection on our site with a manhole that drops about 4m and then runs to the boundary and main sewer. The constraints of the site mean we will need to get as close to it as we can. (The quotes for moving the sewer connection have been high.)

 

Separately we have a brick boundary wall that will be the rain screen for the ground floor of our build. To avoid the expense of a demolish and rebuild could the raft get close enough to avoid this?

 

Grateful for anyone's experience!

[mjc55]

i think that you would need to ask whoever designed your foundation.

[WisteriaMews]

We're currently at the planning stage so don't have a foundation designer / structural engineer on board yet. I appreciate these will be the people that need to give a definitive answer but I was wondering if anyone on the forum and done similar and could share their experience.

[Nickfromwales]

48 minutes ago, WisteriaMews said:

We're currently at the planning stage so don't have a foundation designer / structural engineer on board yet. I appreciate these will be the people that need to give a definitive answer but I was wondering if anyone on the forum and done similar and could share their experience.

It’s down to geotechnical surveys and input from an SE. Trying to short cut and ask questions like this here are (sorry) a total waste of your time, and nothing typed here will be of any value or use whatsoever as none relate to your site   

 

You can bite the bullet now, and do the geotechnical and grounds conditions surveying, test puts and percolation testing etc done, you’ll need these to decide on what type of foundation is required. Also, this will discount the possibility of having to do a piled foundation, in the worst case.

 

With a good engineer anything’s possible, but more info would be needed about where the 4m deep manhole gets its input, from the new house, as you may need to alter this to become a proper backdrop chamber (with such huge inverts).

[saveasteading]

4 hours ago, WisteriaMews said:

if anyone on the forum and done similar and could share their experience.

Yes and no. This would need very detailed consideration and a site survey, just to give this preliminary advice.

After you have had it, may be the time to ask on here for other ideas, which a good SE will be happy to discuss.

 

But do be aware that the term 'raft' is used to mean different things  to different people. Do you mean a heavily reinforced slab that could span over soft spots and support structural walls, or simply a concrete floor?