Alterations to an existing extension without building regs

Swanny3542

Hi all,
We are in the process of purchasing a property with an extension that has no building regs documentation. The extension was built in 1977, therefore a lack of documentation is not unexpected.

On completion of the purchase, it is our intention to make alterations to the extension, extending a few extra meters, changing the roof, adding bifold doors etc. This draws a few questions: 

-As we are altering the extension, will we have to bring this up to current building regs standards, or would it just be the extra bits that we do?
- Is this common, or more common to knock down and start again with current regs and full approval?
- will I face any challenges to knock down the original extension, do I need any approval?
- would it be cheaper to bring the original extension up to current building reg requirements rather than knock down?

Thanks for any advice you can offer.

AdrianC

Only your changes would have to conform to modern BR.

Which would be cheaper? Are there any challenges? A few more details may be required...

Doozergirl

Your extension predates the building regulations.  There's no paperwork to be had.  The extension is what it is.  

Only the changes you make need to conform.   It would be prudent to do sensible things like insulating it properly, if it hasn't been already.   The new roof is a brilliant start.  

user1977

Have a think about it - you know you don't need to bring the original portion of the house up to current standards, so why would you need to do that to the 1970s extension?

Swanny3542

Thanks all for your responses. I should have thought about it as user1977 put it, I was mainly worried about the foundations for the extension, and the significant extra cost that would be encountered if I had to address this to meet current standards. 

I’ve seen multiple examples of costs for an extension, from 1.5k-2.5k sqm, but does anyone know the cost range of a replacement roof per sqm?