Schedule 2 of the Building Regs states that non-habitable buildings are exempt from the requirements of the building regs. That’s fine except it leaves an obvious grey area, being the definition of ‘habitable.’
One rule of thumb is that if the new structure is outside the ‘heated envelope’ then it is regarded as non-habitable. Thus a porch constructed outside the front door would not be deemed to be habitable, nor a ‘bolt-on’ style conservatory, and neither would require building regs. However, if you take the connecting doors off, then the new space is deemed to be habitable. As such, the new structures have to meet all the building reg requirements: i.e. foundations have to be passed, structural stability must be checked, insulation and ventilation must meet regs.
Certain internal works also require building regs approval:
• removing load-bearing walls
• forming a new bathroom or cloakroom
• replacement windows
• replacing boilers
• loft conversions
• major electrical work and all electrical work to kitchens and bathrooms
Most local authorities keep records of building regs approvals going back around 15 years. If you undertake relevant work on your home without building regs approval, you may not be called to account until you come to sell the house when the lack of building regs may come to light.