Groundwork & Foundations Question

Required foundations depth for a second floor extension

I am currently in the process of buying a house which is period but had had an extension registered with the council in 1994 but was never completed and/or checked by the building control. When I visited the house, the estate agent told us that the extension was actually built in 2003 but it does not show anywhere on the council paperwork. All we know is that after a certain period of time, the building control closed the case but never actually controlled the extension when finished. In other words, the extension which did not need planning permission was never checked by building control.

One of the reason for me to want to buy the house is to actually used the current extension and add another floor on the top of it. The fact that I cannot find anything about the current extension is worrying. Am I right and am I in my rights to ask the seller to organise for building control to come over and dig a couple of trial holes just to make to make sure that the extension is sound? I also want to updates the records at the building control that the extension is actually fit for purpose.

Also, if the seller was to accept, building control would come over with a foundation inspector and a structural engineer. I guess if they OK the extension and confirm that the foundation are appropriate for building an extra storey extension, it is all fine? I do not want to have to redo all the work again, or to underpin the extension also.

Also as a matter of interest, what would be the minimum required foundation depth and make so that the extra floor can be built? Can I ask building control if the extension can be used as a base for the extra floor?

Any other thing I should know now before going any further?

Thank you!

1 Answer

Best Answer

Hello , A for a start building control will not come out and dig holes, its upto you or the vender to excavate the holes then ask building control to come and have a look, its not just the depth of the foundation (dig) it also the thickness of the concrete,
The standard asking depth for a foundation is usually 1 mt below finished ground level with up to 450/600 of concrete if its trench fill 450mm wide 450/600 brickwork or 300/400 concrete and 770/825 brick/blocks if its a brickwork construction, hope thats not too confusing

Answered 12th Apr 2014

Rowan Groundworks Ltd

Member since 16 Jan 2013

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