Planning permission for loft conversions and house extensions is normally needed in most of London boroughs but depends on what other home improvements works you have done in the past you may not need permission

If you required a planning permission there are some conditions:

Loft conversion in London
Terraced house, has a volume allowance you have is 40 cubic metres but If you live in a semi-detached house, the volume allowance you have is 50 cubic metres;
Also note that your loft conversion cannot extend beyond the plane of the existing roof slope of the principal elevation that fronts the highway, one more really important restriction is that your loft conversion cannot be higher than the higher part of your existing roof; and you must use materials that are similar to the existing house

There are many other points that you must follow when you planning a loft conversion when it come s to the look and design of the conversion for examples you are not allowed any verandas, balconies or raised platforms as part of your extension, side-facing windows must be obscure-glazed and any opening should be 1.7m above the floor

The most valuable advice that you can get when you are building a house extensions, garage conversion or loft
Conversion is to choose an experienced building company that is able to carry out the work and advice on the best practice, choose the house extensions builders in London