Deep foundation for garage

[bluebaron]

I have an old single skin garage and was hoping to add a room above it.
How ever I’ve Just had the BCO round and he want 2.4m foundations so it looks like the whole thing will have to come down and be rebuilt. I’m also adding a garden room on the side so it’s around 35 linear meters.
That is a lot of concrete!
Need to rethink this!

 

[oldbutnotdead]

Did bco say why they wanted deep foundations? 35m at 2.4 deep x 0.5 wide wld cost a fortune- 42 cubic metres. Plus trenching to that depth will need proper shoring...

 

[bluebaron]

Yep said because I’m on heavy clay and 7m from a load of trees.

 

[bsr]

Piles may be cheaper?

 

[RonnyRaygun]

What are the closest trees? I'm assuming Oak or Poplar if foundations need to be that deep at 7m away? Have you had the soil tested for volume change potential? If low volume change potential you might be able to get away with shallower footings.

Pad and ground beam is an alternative to piles. The pads can be formed by using precast concrete rings inserted to the required depth before filling with concrete.

Might also be worth looking at screw piles if the loads aren't too high.