Excavating a basement with no foundations

5 Jul 2011
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United Kingdom
I want to convert a basement room into habitable space. The existing room height is only 2130mm so I can't afford to lose any height.

Question 1: I think my floor construction is going to need at least a depth of 233mm made up of: Screed and sand blinding (50mm), DPM, Concrete slab (100mm), insulation (65mm) and T&G chipboard (18mm). Have I got this right and/or is it possible to reduce these thicknesses at all and still satisfy Building Regs?

Question 2: The house was built around 1900 and doesn't have any foundations. One of the external walls only goes 140mm beneath the existing floor level, so I'll have to excavate to a depth lower than the bottom of the external wall. :eek: I think I can do this safely by getting my groundworker to excavate and lay the floor (up to the concrete slab) in separate strips. Would this work and how wide would the strips need to be? I'll probably use a structural surveyor to make sure everything is done safely but I'm hoping someone can give me a couple of pointers to help me decide whether the project is viable before I start shelling out cash!

Thanks in advance
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