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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Building Questions >> Foundations for chalet bungalow extension https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1375822322 Message started by olliesquire on Aug 6^th, 2013, 9:52pm

Title: Foundations for chalet bungalow extension
Post by olliesquire on Aug 6^th, 2013, 9:52pm

Hi
We have an existing single storey side extension on our chalet bungalow.
We are hoping to make this existing single storey extension into two storey by building a ‘chalet roof’ on top with dormers - thus creating rooms in the roof (in other words as per the rest of the house).
In theory, we wouldn’t need to redo or add to any of the existing brick walls, but just build the roof upwards from the top of the brickwork….but of course this is assuming that the existing foundations are OK...
With respect to the foundations, the plans I have seen for the single story extension specified foundations “….min 1000mm deep and laid with GEN 3 concrete….”.
However, I spoke to building control today, and they said that in the approved docs, the foundation is “850mm deep into stone” and was approved by BC for the existing single storey extension.
Presumably because the foundation is ‘into stone’, they can be a little less deep?? And presumably this would also indicate good strong foundations..?
They suggested that we dig a trial hole to expose the footings for a BC inspector to inspect to give a view on their suitability – which we will do.
However in the meantime (since we are needing to get a budget together for this asap), what is anyone’s gut feeling as to whether a foundation ‘850mm deep into stone’ might be suitable for adding a chalet roof and dormers. Again bearing in mind that it would appear to me to be just a roof and no additional brickwork!
Or is this not enough info for even a gut feeling…?
Hope someone can help…

Title: Re: Foundations for chalet bungalow extension
Post by woodsmith on Aug 7^th, 2013, 8:32am

From my own experience I would have thought you would be fine, I built an extension onto stone and they were happy with half what you should have. It all depends on what sort of stone you have though and the BCOs view. Best to get digging, it won't take long to get down to 850mm and get the BCO round. You can always fill it back up if you have to wait to start the build.