If I want to build a garage extension onto my home, will the building regulations apply?

Department: Environment Services
Division: Environment Services/Building Control

YES - but a carport extension, open on at least two sides, and under 30m2 in floor area, is exempt. You should ensure that a carport does not interfere with the proper working of a low-level flue outlet from an oil or gas appliance (guidance on the location of flues can be found in Approved Document J).