Single Thickness to Cavity wall upgrade

[silva]

I'm currently making plans to upgrade an old Outhouse and Coal Store on the back of my 1950's end terrace house in to a utility room. The cavity wall from the house extends to incorporate the Outhouse, but the coal store only has a single brick wall construction.
As this needs to be converted to a cavity wall (to satisfy building regs), what do I have to do with the foundations?
The house sits on foundations 600mm below the DPC - not the full 1m now required by Building Regs. Can I just dig to the existing 600mm foundations to start my cavity wall brickwork, or do I have to go to 1m? None of my new walls will be load bearing (apart from their own weight!)
Hope you can give me some advice!
Many thanks!

[thedoctor]

HI Silva, a question for the building inspector I'm afraid. We have, in the past been allowed to simply add an extra 400mm to the side of the existing footings and we have also been asked to go down 1 meter beyond them with an extra 600mm footing. The ground conditions will dictate what you have to do. Take a look at the foundations project on the website and don't forget to come back and tell us the result.

[thedoctor]

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