Whether or not a planner or master builder is required depends first and foremost on whether the work to be carried out is minor or whether it requires planning permission. Minor building projects are understood to be those which involve structural maintenance, renovation or improvements to the building, such as replacing the roof or windows. Where the work only involves a new roof, the work is generally carried out without an additional planner being required. In this case, the roofer takes on the planning work. Bear in mind that not all trades are authorized to carry out design work. For example, changes in weight could require new static calculations to be carried out.