If I want to build an extension to my home, will the building regulations apply? 

Department: Environment Services
Division: Environment Services/Building Control

YES - But a porch or conservatory, built at ground level and under 30m2 in floor area is exempt, provided that the glazing complies with the safety glazing requirements of the building regulations (i.e. Part N: 'Glazing - safety in relation to impact, opening and cleaning'). Your building control service can supply further information on safety glazing. 

You should not construct a conservatory where it will restrict ladder access to windows serving a room in the roof or a loft conversion, particularly if any of the windows are intended as a way of facilitating escape or rescue if there is a fire.