You will need to apply for Building Regulations approval if you plan to convert a garage.
This is because you are changing a non habitable space into a habitable space. This would be classified as a 'material change of use'.
The Building Regulations will help to ensure,
l The garage is safe and sound;
l That it is water and weatherproof;
l It is insulated for comfort and energy conservation;
l It is ventilated to assist healthy living.
Please refer to the guidance booklet on Garage Conversions which can be downloaded on the right (available shortly).