Loft Conversions in Hertfordshire

Most dormer and Velux loft conversions fall under permitted development, meaning no planning permission is needed — provided the dormer does not extend beyond the existing roof plane at the front, and the total volume added is within 40 cubic metres (terraced) or 50 cubic metres (detached/semi). Properties in conservation areas or flats usually need a full planning application. We check this during your free site survey.

The key factor is head height. You need a minimum of 2.2 metres from the top of the ceiling joists to the underside of the ridge beam. Most houses built before 2000 have enough height. We also check the roof structure (cut timber vs. trussed rafters), floor joist strength, and staircase positioning. All of this is assessed during your free site survey.

A dormer extends outward from the rear roof slope, creating a box-shaped addition with full headroom. A hip-to-gable extends the sloping side of the roof to a vertical wall, increasing the overall loft floor area. Hip-to-gable is typically only possible on semi-detached and detached homes with hipped roofs. Many homeowners combine both — a hip-to-gable with a rear dormer — for maximum space.

A rear dormer loft conversion typically costs £38,000-£55,000. A hip-to-gable with rear dormer ranges from £45,000-£65,000. Mansard conversions start from around £55,000. The price depends on the existing roof structure, access, and your choice of finishes for the bedroom and en-suite. Our quotation is fixed-price and includes structural steelwork, insulation, plastering, electrics, plumbing, and building control fees.

If your loft conversion involves work on a party wall (common on semi-detached and terraced houses), you will need to serve a party wall notice. Rear dormers on terraced houses can sometimes affect neighbours' light, though this is rarely a planning issue for permitted development. We discuss all of this during your consultation.