Flat Roof Dormers in West Sussex
If you are weighing up flat roof dormers in West Sussex, we survey the roof, tell you what is actually achievable, and price it properly before anyone commits.
Flat Roof Dormers — indicative geometry
Flat Roof Dormers for West Sussex homes
Most of the dormer work we take on around West Sussex is on Victorian and Edwardian terraces, interwar semi-detached houses and post-war bungalows, where the ridge height and the position of the existing purlins set the limits.
A flat roof dormer projects square from the roof slope with a shallow-fall flat top, usually finished in GRP fibreglass, EPDM or single-ply membrane. Because the walls are vertical and the ceiling is level, you keep full standing height right up to the window — which is why it is the default choice on rear elevations where planning is under permitted development.
Key specification
| Typical projection | 1.8m – 6.0m wide |
|---|---|
| Roof fall | 1:80 minimum to the rear |
| Roof finish | GRP, EPDM or single-ply membrane |
| Cheek finish | Tile-hung, GRP, lead, zinc or timber |
Planning and building control in West Sussex
Rear dormers on houses often sit inside permitted development, but the volume allowance is consumed by any previous loft or rear extension — so we check the planning history for the address before we say yes.
Building regulations approval is separate and always required. We submit the application, book the inspections around the programme and hand you the completion certificate at the end — the document a buyer's surveyor will ask to see.
Why homeowners in West Sussex use us
We would rather tell you at survey that your ridge height will not take what you want than take a deposit and find out in week three.
The quickest route is a photograph of the rear elevation over WhatsApp — we can usually tell you what is feasible before anyone visits.
Other dormer work in West Sussex
FAQs
Flat Roof Dormers in West Sussex — FAQs
Can you convert an existing Velux loft to a dormer?
Yes, and it is usually a shorter job than starting from scratch because the floor, staircase and services already exist. We verify the existing floor structure and any previous building control approval first, then cut and form the dormer into the finished room. Expect the room to be out of use for three to five weeks.
How disruptive is a dormer build?
Less than people expect, because most of the work happens above your ceilings and is reached from the scaffold. The noisy phases are opening up and installing steels, typically two to four days. Once the staircase is cut in there is dust and traffic through the house, and we sheet and protect the route for that period.
Do dormer windows need to be fire escape windows?
In a loft conversion, at least one window in each habitable room generally needs to meet escape requirements — a clear opening of at least 0.33m², minimum 450mm in both height and width, with the bottom of the opening between 800mm and 1100mm above floor level. We specify the opening lights to meet this as standard.
Do I need planning permission for a dormer window?
Rear dormers on a house often fall under permitted development, provided the dormer is set at least 200mm back from the eaves, sits below the ridge line, uses materials similar in appearance to the existing house, and stays within the volume allowance — 40m³ for a terrace, 50m³ for a semi or detached. Front-facing dormers, flats and maisonettes, listed buildings, conservation areas and any property with an Article 4 direction all need a full planning application. We check the constraints on your specific address before we quote.
Will my roof be open to the weather?
No. The roof is only opened once the scaffold, temporary weather protection and materials are all on site, and the dormer is made weathertight — structure, deck, membrane and temporary glazing — before the crew leaves at the end of the opening-up phase. We do not open a roof on a Friday afternoon.
Find out what your roof will take
A free measured survey in West Sussex tells you what is achievable, what it needs, and what it costs — before you commit to anything.