Re using existing footings and slab for new ss extension

[drpepe]

Hi all,

 

my 1st post here after reading loads of really helpful information on this forum.

 

As per the thread title we have plans for a single storey rear extension on our 1930s semi on the footprint of an existing c2003 conservatory. The planned extension is approx 5x5m , flat roof with 2 roof lights and sliding doors at rear.
 

We bought the house last year and the previous owner had told us they put in ‘extra foundations’ but decided on a conservatory rather than full extension. Upon digging a couple of trial pits on different conservatory elevations, we found  750mm deep footings. A visit from building control concluded that they were happy for us to demolish the conservatory down to dpc and build from there. 
 

We are getting a quote from a recommended builder, and he has commented whether bc are going to back this up with ‘calculations and sign off’, saying that if there was foundation shearing in the future we would need that to claim on someone’s insurance. To be fair, the builder is within their rights to want some sort of cover given the foundations are not their own work/responsibility. 

 

1. Does bc control approval come with this sort of guarantee? (Afaik, no it doesn’t!)

2. Presumably the builder will want some sort of clause to avoid responsibility for any issue with the foundations. 

3. I could get an SE to examine and calculate loads, but they may play it safe and say these foundations are no good. In which case I am back to square 1. 
 

does anyone have any thoughts on how to proceed here?

 

many thanks 

Edited March 20, 2022 by drpepe

[nod]

I’ve done a couple like this 

Both occasions I’ve pulled the foundations out and left the slab in place 

I’m surprised that BC haven’t insisted on this 

BC sign off comes with no guarantee 

Your builder is unlikely to take responsibility for any structural elements of the extension 

I would start a fresh 

[drpepe]

Thanks Nod. 
 

do you stay start afresh because you think there would be a big risk of a problem of fracturing, or due to the grey area of who is responsible?

there’s quite an issue of cost of removing and replacing footings due to access.  

6 minutes ago, nod said:

I’ve done a couple like this 

Both occasions I’ve pulled the foundations out and left the slab in place 

I’m surprised that BC haven’t insisted on this 

BC sign off comes with no guarantee 

Your builder is unlikely to take responsibility for any structural elements of the extension 

I would start a fresh 

 

[MJNewton]

No advice to offer, but posting just to say we reused our conservatory footings for its replacement extension. Like you the BCO just wanted some inspection pits dug so he/we could check they were okay. 

[nod]

10 hours ago, drpepe said:

Thanks Nod. 
 

do you stay start afresh because you think there would be a big risk of a problem of fracturing, or due to the grey area of who is responsible?

there’s quite an issue of cost of removing and replacing footings due to access.  

 

In my case BC wasn’t over keen on me reusing foundations So I had little choice However in your case if BC originally signed the foundations off It would make a big difference 

If they didn’t it may bite you on the arse at a later date 

It’s a get out of jail card for your builder at the very least 

Unless he put these foundations in originally