Velux and skylight installation, roof lights and dormer windows across Portsmouth. Coastal-grade flashing is essential here — standard zinc corrodes in salt air. We install and flash correctly for the south coast, on pitched and dormer roofs alike.
Velux and skylight installation in Portsmouth costs £1,200 to £3,000 per window in 2026, with dormer windows priced per scope. Coastal salt air demands upgraded flashing kits — standard zinc corrodes fast here. We install roof lights and dormers on pitched and flat roofs with correct coastal detailing. Free survey — call 0239 307 1334.
Adding natural light to a loft or top-floor room is one of the most popular Portsmouth home improvements, and it covers three related but distinct jobs: fitting a Velux or other roof window into a pitched slope, installing a flat rooflight into a flat or low-pitch roof, and building or reglazing a dormer window that projects from the roof. Each involves cutting into the weatherproof envelope of the roof, and each lives or dies on the quality of the flashing that reseals it. In Portsmouth's coastal environment that flashing specification is not a detail — it is the difference between a dry installation and a leak within a few winters.
A roof window is only as watertight as the flashing kit that seals it to the surrounding roof. Manufacturers supply standard flashing kits rated for typical inland conditions, but Portsmouth is not typical inland — salt-laden air corrodes standard zinc flashing components years ahead of their expected life. On Portsmouth installations we specify upgraded coastal or copper flashing kits as standard, because a window that leaks two winters after fitting costs far more to remedy than the modest upgrade cost. This is exactly the kind of local specification a national installer following a standard fitting manual will miss.
Portsmouth's tight island geography, where extending outward is often impossible, has made loft conversion and rooflight installation especially common — and different areas convert differently. The larger Victorian and Edwardian properties off Albert Road in Southsea and the bigger houses of Old Portsmouth suit full dormer conversions that add real floor area. The dense two-storey terraces of Fratton and North End more often take rooflights or modest dormers within permitted development. The 1930s semis of Cosham and Drayton have generous, simple roof structures that accommodate standard Velux sizes cleanly. We assess the roof structure and the planning position before recommending rooflight, dormer or full conversion for each property type.
A dormer projects from the roof slope to add headroom and light, and on Portsmouth's Victorian terraces it is the standard route to a usable loft room. The roofing challenge is the dormer's own roof — usually a small flat roof facing directly into coastal weather — and its junctions with the main slope, which are prime leak points if flashed poorly. We build dormer flat roofs in GRP fibreglass for coastal durability, not felt, and flash the cheeks and junctions with upgraded materials. On party-wall terraces we also manage the rafter configuration at the shared wall, which dictates where the dormer can sit. Conservation area properties in Old Portsmouth and parts of Southsea may need planning consent for a visible dormer — we establish that before quoting.
Beyond pitched-roof Velux windows, Portsmouth's many flat-roof extensions and dormers take flat rooflights that flood single-storey rear rooms with light. These sit on an upstand kerb built into the flat roof, and the waterproofing detail where the kerb meets the membrane is critical — on a coastal flat roof it faces standing water and salt exposure. We install rooflights as part of a GRP or EPDM flat roof so the kerb and membrane are a single integrated system, rather than retrofitting a rooflight into an aged felt roof where the junction will inevitably fail. Getting the flat-roof and rooflight specification right together is how you avoid the ponding leaks that plague poorly detailed installations.
| Installation | Cost Guide | Notes |
|---|---|---|
| Velux / roof window supplied & fitted | £1,200–£2,000 | Coastal flashing kit included |
| Large / centre-pivot roof window | £1,800–£3,000 | Bigger units, coastal detailing |
| Flat rooflight (on new flat roof) | £1,400–£2,800 | Integrated GRP/EPDM kerb |
| Dormer window (build, per scope) | £3,500–£9,000+ | GRP dormer roof, coastal flashing |
| Dormer reglaze / window replacement | £800–£2,000 | Existing dormer |
| Coastal flashing upgrade | Included | Standard on all Portsmouth work |
Roof windows installed within permitted development must not project more than 150mm beyond the roof plane, under the General Permitted Development Order.
Source: General Permitted Development Order
We assess your roof structure and planning position, specify coastal-grade flashing, and quote in writing for Velux, rooflights or dormers. No call-out fee.
Call 0239 307 1334"Two Velux in our Cosham loft — they fitted upgraded coastal flashing without me asking and explained why standard zinc corrodes here. Bone dry through two winters."
"Dormer on our Southsea terrace loft conversion — GRP roof, proper flashing at the cheeks. They handled the conservation area check before quoting. First class."
"Flat rooflight over our kitchen extension — they built it into a new GRP flat roof rather than cutting into the old felt. Floods the room with light, no leaks."
A Velux or roof window supplied and fitted costs £1,200 to £2,000, with larger units £1,800 to £3,000. Coastal-grade flashing is included as standard — essential in Portsmouth's salt-air environment.
Standard zinc flashing kits corrode years early in coastal salt air. We fit upgraded coastal or copper flashing as standard, because a leak two winters after fitting costs far more than the modest upgrade.
Dormer windows are priced per scope, typically £3,500 to £9,000-plus for a built dormer including its GRP roof and coastal flashing. Reglazing an existing dormer costs £800 to £2,000.
Roof windows within 150mm of the roof plane are usually permitted development. Dormers on principal elevations, and any roof change in conservation areas like Old Portsmouth, may need consent. We check before quoting.
Yes — best done as part of a new GRP or EPDM flat roof so the kerb and membrane are one integrated system. Retrofitting into aged felt creates a junction that will eventually leak.
GRP fibreglass, not felt — the small dormer flat roof faces direct coastal weather and needs the seamless, salt-resistant durability GRP provides. We flash the cheeks and junctions with upgraded materials.
Yes — seal failure, flashing and full replacement. See our dedicated Velux repairs page, or call 0239 307 1334 and we'll advise whether repair or replacement is the better option.
No call-out fees. No obligation. Local Portsmouth roofers.
0239 307 1334