Garage upgrade

Hi,

We currently have an old detached garage we are looking at upgrading to an office / spare room.

It’s a single brick structure and we will change roof and doors.

Question is how best to waterproof and insulate the single brick to ensure damp etc doesn’t become an issue down the road.

Thanks for the advice!

It would likely be cheaper to knock it and re-build than to upgrade it to meet current regs to use as a habitable space. Remember, converting to a spare room is not an exempted development and planning would be required.