If I am not extending my property and only changing interior, do I need Planning Permission?

Hi isfl, the majority of garage conversions fall within your house's 'Permitted Development Rights' which enables you to make certain changes to your home without the need for planning permission. In order to obtain written confirmation from the council that the changes you propose don't require planning permission you can apply for a Certificate of Lawfulness. You will still need Building Regulations approval for the garage conversion, putting in the mezzanine and if you are knocking through a load bearing wall in bedroom 3 to access the en-suite.

You might need planning, best to contact your local bco via the Council, you will probably need building regs as well. Small alterations are okay, but your changing use of garage to habitable.

Probably not but you will need to call building control at your local authority, plus structural engineers calculations for any structural or load-bearing alterations.