1. At the outset, you are allowed to convert the roof space area without planning permission as it is exempted development within the Irish Planning Acts. However, to this general rule, there are a number of caveats. Firstly, you cannot extend the roof space beyond the shadow of the building as currently constructed without seeking planning permission for any extension. This means that your dormer out the rear roof must not extend the current shadow of the building. It must not overhang the front wall, nor any side wall. It can extend beyond the rear wall so long as any extension does not exceed 40 square metres in area, as this is the exempted development limit for rear extensions. There is no problem with the conversion of the attic space, as this is already considered liveable space as it is part of the existing building even if unused currently. There is no problem with ownership of the roof area. If you own the top flat you own this roof space above your flat. Additionally, so long as you do not go above the point of the roof in your dormer, you are not exceeding the shadow of the house and so it is exempted development. However, I would get an architect to assist you with the practical design if there is a possibility of exceeding the shadow of the existing building.