What is a dormer loft conversion?
A dormer is a structural box that projects out from the existing roof slope, with vertical side walls and a flat or shallow-pitched roof. Inside, the dormer creates a rectangular volume with full standing headroom — typically 2.3m to 2.4m floor to ceiling — which is what turns a cramped attic into a properly habitable bedroom. On a London terrace, the dormer is almost always built on the rear roof slope facing the garden so it cannot be seen from the street. This is what allows it to fall under permitted development rights in most boroughs, provided the cubic volume stays within the 50m³ allowance and the dormer is set 200mm back from the eaves. The dormer wall is framed in timber or SIPs, insulated to current building regulations (typically 150mm PIR between studs plus a service void), and clad externally in tiles, slate, lead, zinc, or composite cladding to match or complement the existing roof. Inside, the new floor sits on steel beams that span the existing party walls, transferring loads down through the structure rather than relying on the original ceiling joists, which were never sized to carry habitable rooms.
Is your house suitable for a dormer?
Most Victorian, Edwardian and inter-war London terraces and semis are excellent candidates. The key constraints are head height, roof pitch and planning status. We measure the existing ridge to ceiling joist height during the site survey: anything above 2.3m gives us comfortable working room once the new floor is installed. Properties with a roof pitch shallower than about 30 degrees rarely deliver a usable dormer, although hip-to-gable conversions can help by adding gable wall to the side. Flats, maisonettes, mansion blocks and any property in a conservation area or listed building will need full planning permission rather than permitted development, but the dormer is still buildable in most cases — the design simply needs to be more sympathetic, often using tile-hung cladding or zinc instead of render. We carry out a free desk-based planning assessment before quoting so you know exactly which route applies to your property.
Planning, party wall and building regulations
Permitted development is the most common route for rear dormers in London. To qualify the dormer must sit on the rear roof slope, be set back at least 200mm from the eaves, use materials similar in appearance to the existing house, not exceed the original roof ridge in height, and stay within 40m³ for terraces or 50m³ for semis and detached homes. We submit a Lawful Development Certificate (LDC) to the borough on every PD job — this is your legal proof, valuable when you sell. If you sit in a conservation area, Article 4 zone, or have already used some of your PD allowance with previous extensions, full planning is required and we handle that submission too. Building regulations apply in every case: fire-rated stair enclosure with mains-linked smoke alarms, structural calculations for the new floor steels, insulation to current Part L standards, and Part P-certified electrics. Party wall agreements are needed if any new steel bears on a shared wall — we serve the notices and manage surveyor appointments on your behalf.
The build process, step by step
Week one: scaffolding goes up, the existing roof is stripped back, and a temporary weatherproof crash deck is installed so the rooms below stay watertight throughout. Week two to three: structural steels are craned in and bolted, the new floor joists are fixed across the steels, and the dormer carcass is framed and sheeted. Week four: roof finishes are installed (typically EPDM rubber, GRP fibreglass, or single-ply membrane), external cladding goes on, and the existing roof slope is tiled back in. Week five to six: stairs are fitted, plumbing and electrics are first-fixed, insulation is installed and plasterboard goes up. Week seven to eight: plastering, second-fix electrics and plumbing, joinery, painting, flooring and snagging. We run a single project manager per build, post weekly photo updates to a private project portal, and book the building control sign-off inspection ourselves at completion.
What's included in our fixed-scope quote
Our dormer loft quote includes architectural design, structural engineer calculations, planning or LDC submission and fees, building control application and fees, party wall surveyor instructions, scaffolding, demolition and waste removal, structural steels and floor joists, dormer carcass and roof structure, EPDM or GRP roof finish, external cladding, double-glazed windows and rooflights, fire-rated stair with mains-linked alarms, internal stud walls and door linings, full insulation pack, plasterboard and plaster skim, complete first and second-fix electrics including a new consumer unit circuit, central heating extension including new radiator and TRVs, hot and cold water for the ensuite, full bathroom suite (within an agreed PC sum), wardrobe carcassing if specified, painting and decoration, and final clean. There are no provisional sums for structural work and no day-rate labour. Anything quoted as a PC sum (kitchen, bathroom suite, flooring) is fully transparent — you choose the actual product within the allowance and only pay extra if you upgrade.
Choosing your dormer layout
The most popular London dormer layout is a master bedroom across the rear with the stair landing leading into an ensuite shower room positioned over the existing bathroom below to keep services short. A walk-in wardrobe or study is often tucked into the eaves where headroom is reduced. On wider properties a full-width dormer can accommodate two bedrooms plus a Jack-and-Jill shower room. Where head height allows, an L-shaped dormer over the rear closet wing gives an enormous floor area — see our dedicated L-shape page for that variant. Window placement matters: Velux rooflights on the front slope wash the room with natural light without affecting planning, while a French door and Juliet balcony on the rear dormer wall opens up garden views without needing a balcony platform.
Why direct labour matters
Most London loft companies subcontract the build to gangs paid a fixed price per dormer. The gang's profit margin is whatever they can cut from the spec, which is why so many lofts end up with single-skin party walls, missing fire breaks, under-sized steels, and acoustic problems that only show up after handover. We employ our carpenters, plumbers, electricians and decorators directly. Pay is hourly not piecework. That removes the incentive to rush and means the same people you meet at survey are the ones on site every week. Our snag rate at handover is under three items on the typical dormer — industry average is closer to twenty-five.
