Foundation depth 1650mm

Grz.26

Hello.

I would like to put to the forum a problem I've had with the foundation depth of a extension I am planning. The architect has said "new foundations taken to depth 1650mm below existing drain invert"
there is a drain near the foundations and the foundations run 500mm 1' 8" from it.

We have had one builder say he does not want to do this as it is really deep. And underpinning will be neccessary.

Is this a problem I'm going to have with all builders? Can anyone shed any ideas/light on this.

Kind regards

Richard

Kiran

What are you building, and what type of soil do you have? A foundation of 2150 below FFL seems very deep. Has there been any reasoning for it? If you have anymore information then an alternative foundation design may be possible

DVardysShadow

Go back to your architect and clarify. It is understandable that the builder does not want to do it, but if he priced on it, then do it he must.

Grz.26

He has not yet priced and most likely wont. I can post a link to the planning portal on here, but bit reluctant as has all personal details on here. I am building a side return extension on my 2 up 2 down end of terrace house.
Plans show 590 wide, mass concrete trench. I couldn't tell you what type of soil. Im sorry. The builder said the drain is too close to foundations and too risky as may damage drain. Maybe his being over cautious.?? maybe not.

dander

I know when I talked to the water company about building near a public sewer, they said that if you went too close you'd have to take foundations below the level of the sewer, so that none of the weight of the building is being carried on the sewer.

Has your architect done this on the advice of the water company?
It does seem that the foundation would be very close to the drain, so maybe the builder is worried about who would be liable if it got damaged in the digging.

Grz.26

I see. So it has to be that deep most probably so not to put any weight on the drain. I shall try and get some more advice for other builders.

Plasticman

It sounds like your architect has designed the foundations in line with the requirements of the water company. You need to do this if you are building over or near a sewer. The water companies often have slightly differnt rules, but here any wall running parallel with the sewer must be at least 500mm away and be below the sewer invert level.

I assume that your architect means that the foundations must be at a depth 1650mm - not 1650mm below the invert level which would seem excessive and (depending on the depth of your sewer) might frighten off a few builders!

Grz.26

Plasticman, this is how it is. I have clarified it with my architect. I was going to gif the foundations my self, as i have asked the question on here. But with them being so deep, is this still a good idea?

Thanks for your help.