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timber framed extension

Postby lioness » Mon Aug 17, 2009 6:48 pm

Can anyone help!!!!
We are having a timber framed extension built. This is going onto the back of our garage which attached to the side of the house, the extends to the back off the house. Which in total is 6.21 m2. The extension is built entirley of a light wood timber, it has been placed on to a concrete base which is 18 inches thick.. The builder who is helping us and is a friend of ours, has gone and had a row with the building inspector. He is now saying he wants the footings 1 & 1/2 meters thick. ?

The house is built on Clay, does this sound correct. Can anyone advise?

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Postby stoneyboy » Tue Aug 18, 2009 9:53 pm

If the extension is going to be a domestic living space (rather than a conservatory) then I would expect to dig foundations in clay to a depth of 2m. Your builder should have discussed this with the BI at the start of work and an inspection should have been made at the 'foundations dug' stage.
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Postby AndiePricie » Wed Aug 19, 2009 8:09 am

Hi The conrete base is unsuitable for an extension. If you were building a conservatory that is exempt from Building Regulations it would be fine.

The concrete and the clay sub base would be alble to carry the loads for the timber framed extentsion however, because it classed as an extension the foundations will need to be constructed to comply with Approved Document A. Generally this means that in clay strata you would need dig down 900mm - 1000mm minimum, if there are trees or drains around it will need to go deeper. The Building Inspector has probably calculated the depth because there are trees present.
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Postby AndiePricie » Wed Aug 19, 2009 10:58 am


Two meters is far too much unless there are trees - general guidance is one meter in clay.
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