Two separate consents, and the one people skip is the one that causes trouble at sale.
Arrange a site visitPlanning permission and Building Regulations approval are separate consents with separate purposes. Planning is about what the building looks like and how it affects the street and the neighbours. Building Regulations are about whether it is structurally sound, adequately insulated and safe to escape from in a fire.
Many loft conversions need no planning permission at all. Every loft conversion needs Building Regulations approval. Work carried out without it is the item that most often holds up a sale, because the buyer's solicitor asks for the completion certificate and there isn't one.
Most loft conversions in Wales proceed under permitted development, which is a national grant of permission subject to limits. The volume allowance commonly cited is around 40 cubic metres of added roof space on a terraced house and 50 cubic metres on a semi-detached or detached house, including any earlier roof additions — so a previous owner's work counts against your budget.
The conditions attached to it matter at least as much as the volume:
Permitted development rights for roof alterations are removed on listed buildings, in conservation areas, and where an Article 4 direction has been made. Cardiff has a number of conservation areas, and the boundaries do not necessarily follow what you would expect from the character of the street, so check your specific address against the council's map rather than assuming from the houses around you.
None of this blocks a conversion. It means a full application, a design that responds to the local context, and a determination period built into your timeline. In some conservation areas a mansard or an internal rooflight conversion is far more likely to succeed than a large box dormer.
If you share a wall — any terrace or semi — cutting into it for beams, or building a gable up to the boundary, engages the Party Wall etc. Act. Notice has to be served on the adjoining owner, and there is a statutory notice period before work can start. It is routine and usually uncontentious, but it is the single item most likely to delay a start date, so serve it early.
Establish head height and roof type first, because they decide what is possible at all. Then check conservation area and Article 4 status, because that decides which route you are on. Then design, then structural calculations, then Building Control — and a planning application in parallel if one is needed. Serving Party Wall notices early runs alongside all of it. Doing this in a different order is how people end up paying for drawings of something they were not going to be allowed to build.
A short site visit tells us the roof type, the head height and where the stairs can land — which is most of what decides the design and the price. We will tell you if a conversion is not the right answer for your house.
Arrange a site visitAll loft conversions