Most loft renovations can be done without planning permission, especially when converting a loft into attic storage. If the space is being renovated into a living space, complete with a staircase and a raised skylight roof, you should check with your local building authorities before setting to work on any physical renovations.
It is important to check your local building codes before you begin a project. Building codes can be different from city to city, or even based on where in the city you live. If you're converting a loft in a residential building, you'll also have to adhere to all electrical and plumbing codes that apply or that fall under the jurisdiction of your building regulations. Some loft conversions do not need planning permission if they fall under the category of non-conservation area residential and if the room is only being used for storage.
If a dormer or dormers are being formed where the volume exceeds that permitted, planning permission is required. Likewise if a hip-ended roof is to be changed to a gable-ended roof, or a dormer on the back addition is proposed, planning permission may be required. Dormers must not project above the ridge, and if storage capacity is likely to significantly increase the load on existing ceiling joists, an application is required. Applications are formally checked by a Building Control Surveyor, who makes sure all problems are resolved before applications are approved.
Because most loft spaces were not created with the intention of additions, the ceiling joists may not be strong enough to support the structure once additional weight is added. You'll have to ensure the structural strength of your loft, which might include replacing load-bearing walls, the first floor lintels and the ceiling joists. In most cases, you'll have to add larger floor joists, at the very least. If surveyors find a wall to be load-bearing, its construction and foundation must be exposed for assessment. Steel beams are often required to support the new floor joists. Any beams, beam bearings, posts, trimmers and connection details should be justified by calculations, and you'll likely have to supply copies to be checked by the authority. Beams must not bear in to chimneys or the party wall between chimneys. Rafters are to be doubled up on either side of the roof lights.
In case of fire, a safe means of escape needs to be provided, which means that the staircase out of the loft must discharge near an exit door and not into a room. Staircases are to be enclosed by a door that can withstand 30 minutes of fire damage. All doors, excluding bathroom doors, as well as the basement and first floor ceilings must be tested and made to withstand 30 minutes of fire damage. All door frames must be inspected at the time of renovation to be up to fire code.