When is an existing loft extension not an extension

[EdwardianMonster]

I bought an Edwardian house that had a 1974 loft extension.
Planning Permission from 1973 details kitchen & bathroom with front and back dormers.

Now its old and badly needs some updating.
Every loft type builder I offer it to declares it wouldn't meet modern building regs and needs to be entirely demolished and replaced at vast expense.
That's true of the entire house - not just the loft.

Admittedly no steel beams under the floor, 6x3 timbers, but its been in use near 40 years without cracking the ceilings below never mind falling into the rest of the property.
So is there guidance on where you need to reverse date building regs onto what has existed for 30 years+ when you want to update.?

 

[jeds]

You don't need building regs for general decorative refurbishment. You will need regs if you alter structure, access or layout or if you change any of the existing fire protection. In fact, altering those could bring the whole raft of regs into play. Apart from that you only need individual regs on controlled services. That's basically heating, electrical and windows.