Extending Basement Under House

I live in a house with a basement kitchen that extends under only part of the house. This includes the rear addition and an area in the main house under the staircase (to provide a stairwell for the basement). The parts of the house that do not currently have a basement have a huge sub-floor void almost as deep at the basement (2m+). The difference being made up of loose rubble etc. It seems that the foundations are at the same level thoughout the house (I guess this has to be the case?). I would like to extend the basement further under the house to provide a second bathroom. What are the gotchas if any? Do I need planning permission? Building control? How should I proceed? Any help would be gratefully received.
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"What are the gotchas if any?" [..]
fire safety, we have a similar layout and were going to convert the existing rear section into a utility room with exit into garden and up stairs to ground floor. the newly dug out section, under the living room, was going to be a playroom. BCO told us it wasn't possible because there would only be 1 escape route if a fire broke out in the utility room, however, we could have them the other way round as the main escape route from the playroom would be direct into the rear garden. there are also issues with ventilation.
"Do I need planning permission?" [..]
we were told no by the BCO and builder giving the quote
"Building control? " [..]
yup
"How should I proceed?" [..]
contact the BCO with your drawn up plans and get him to come out, he'll give you a lot of info and help (well ours did).
Les
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Find a structural engineer (talk to the BCO for hints, if you're lucky). They'll be able to tell you if the foundations would be adequete and how safe it is to dig out the rubble. They will also tell you if a little underpinning would be beneficial. You WILL need building control approval. Not sure about planning for this.
Christian.
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First thing to do is to dig a couple of test pits and see how deep those walls really are. Our cellar has a void under some rooms, but the footings are only half the depth of the cellar.
If you on clay soil it is a bad idea to do any digging nearer than 1m to a wall, and make sure not to go below the depth of the footings, as the clay will shrink as it dries out.
J.
--
John Rouse

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Thanks for your help. The footings are definitely all at the same level. But fire regulations is something I hadn't thought of. I think I will get in touch with the local BCO. Do they charge for advice?
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