Garage raft questions?

[angelboy]

I'm rebuilding a garage and have searched the forum (and paving expert) for info on concrete rafts but still have a few questions regarding the design.

The garage is 30sqm so doesn't require building regs but I'm confused as to what constitutes 'adequate construction' against the 'minimum guidelines' of building regs?

It's 3.4m x 8.8m, single skinned brick construction with brick piers at 3m centers, hipped roof construction with clay rosemary tiles.

I was planning to built a steel re-enforced raft, 150mm on 75mm sand blinding over a DPM then 150mm MOT 1 and 300mm wide x 400mm deep foundations (not re-enforced) extending for the brick piers.

If it were going through building regs then the spec for the foundation depths would be 2.2m due to being 2m from a Hawthorn hedge and medium density clay (NHBC guidelines). This would then bust the water table which is about 1.5m below ground.

What can I get away with without going overboard. The garage I'm rebuilding has been perfectly fine for 60 years although I don't know what the walls are sitting on until I pull it down.

[stoneyboy]

angelboy,
I doubt you will have success with a raft foundation given the sub-soil conditions you describe. You should get a specialist in to have a look at your foundations once you have dug them, forum members will not be able to advise you without seeing the subsoil.
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