Just a word of advise concerning loft conversions.
Planning permission is not normally required. However, permission is required where you extend or alter the roof space and it exceeds specified limits and conditions details below:-
A volume allowance of 40 cubic metres additional roof space for terraced houses*
A volume allowance of 50 cubic metres additional roof space for detached and semi-detached houses*
No extension beyond the plane of the existing roof slope of the principal elevation that fronts the highway
No extension to be higher than the highest part of the roof
Materials to be similar in appearance to the existing house
No verandas, balconies or raised platforms
Side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor
Roof extensions not to be permitted development in designated areas**
Roof extensions, apart from hip to gable ones, to be set back, as far as practicable, at least 20cm from the original eaves
Its important to bear in mind that any previous roof space additions must be included within the volume allowances listed above. Although you may not have created additional space a previous owner may have done so.
Or that the property has had its permitted development rights removed. I would recommend discussing your proposal with your local planning authority before commencing.
A useful site for all information concerning permitted development rights is
www.permitteddevelopment.net.
hope this helps.