Where more than 25 per cent of a ceiling below a cold loft space or flat roof is being replaced then building regulations would normally apply, and the thermal insulation of that ceiling would normally have to be improved.
Work to refit a kitchen or bathroom with new units and fittings does not generally require building regulations approval, although drainage or electrical works that form part of the refit may require approval under the building regulations.
The 'Low or Zero Carbon Energy Sources: Strategic Guide (LZC)' supports the inclusion of low or zero carbon energy sources in Part L of the Building Regulation and Approved Documents L1A, L1B, L2A and 2B. Chapter 4 deals with micro-CHP.
If you want to put up small detached buildings such as a garden shed or summerhouse in your garden, building regulations will not normally apply if the floor area of the building is less than 15 square metres and contains no sleeping accommodation.
The regulations define converting a home into a shop as a 'material change of use' and specify the requirements with which, as a result of that change of use, the building, or the relevant part of the building, must comply.