Roofing Options for Loft Conversions
Velux / Rooflight Conversion
The simplest and cheapest option — Velux rooflights cut into the existing roof slope without changing the roof form. Planning permission is usually not required for rear-elevation rooflights on standard Horsham properties. Cost for the roofing element: £600–£1,600 for 1–2 windows. The limitation is headroom — if the existing pitch doesn't provide adequate standing height, rooflights alone won't solve it.
Dormer Conversion
A dormer extends the roof slope outward to create a vertical window and additional headroom. Rear dormers are common on Horsham's semi-detached stock. The roofing element includes a new structural frame, lead flashings at all junctions, a flat or pitched dormer roof, and cheek cladding. We carry out the full roofing package on dormer conversions.
Hip-to-Gable Conversion
On hipped-roof properties — common on 1960s–80s Horsham detached houses — extending the hip to a vertical gable creates significantly more loft space. This is a major structural and roofing project requiring planning permission. It creates the most usable space on the right property type but is the most expensive option.
Dormer Flashing — the Critical Detail
The junction between a dormer and the main roof slope is the most vulnerable detail in any loft conversion roof. Poorly executed dormer flashing is the most common roofing call we receive from Horsham properties that had conversions 10–20 years ago. We install all dormer flashings in code-weight sheet lead, correctly stepped and fixed into the masonry or timber substrate — not surface-applied mastic which fails within years.
Permitted Development — What Actually Qualifies
The permitted development rules for loft conversions are more specific than they are sometimes described. The volume limits (40m³ for semi-detached, 50m³ for detached) apply to the additional volume created by the conversion, not the total roof volume. Dormers on principal elevations (those visible from the highway) always require planning permission, regardless of size. Permitted development only applies to dwellinghouses — flats and maisonettes are excluded entirely. If your property is in an Article 4 Direction area (which removes permitted development rights), all conversions require planning permission regardless of size. We identify permitted development status during the survey visit and advise accordingly before any work is committed.
Structural Implications — What the Roof Survey Covers
Before any loft conversion, the existing roof structure needs assessment. Standard cut-timber roofs (rafters and ridge board) can usually accommodate conversion with relatively minor structural modifications. Trussed rafter roofs — common on Horsham properties built from the 1960s onwards — cannot be modified without engineered replacement of the truss structure, which is a more substantial structural project. We identify the roof construction type during the survey and advise on the structural engineering implications before any roofing element is quoted. We work alongside structural engineers on trussed rafter conversion projects.
Building Regulations for Loft Conversion Roofing
The roofing elements of a loft conversion must comply with Building Regulations Part A (structure), Part B (fire safety), Part C (moisture), Part L (energy efficiency) and Part F (ventilation). The structural element is typically covered by the engineer's calculations and our installation. Fire safety requires fire-rated boards at the conversion ceiling. Moisture control requires breathable membranes and correct ventilation. Energy efficiency requires insulation to the prescribed U-value at rafter level. We work to Building Regulations compliance on all loft conversion roofing work and provide the required documentation for Building Control sign-off.
Getting the Work Done in Horsham
All surveys in Horsham are free with no call-out fee. We attend within 3–5 working days for planned surveys and aim to reach emergency call-outs within 2–4 hours. Every job receives a written, itemised, fixed-price quote before any work starts — no verbal estimates and no bills that exceed the accepted written quote.
We are NFRC registered and carry £5 million public liability insurance. All work carries a written 10-year workmanship guarantee backed by a named, verifiable local contractor. Guarantee and insurance documentation is provided on request before any survey visit.
We cover Horsham and the surrounding West Sussex area including Roffey, Broadbridge Heath, Southwater, Billingshurst, Pulborough, Storrington, Henfield, Crawley, Burgess Hill, Haywards Heath, East Grinstead and Worthing. Call 0140 358 1272 to arrange a free survey.
Last reviewed: July 2026 by Horsham Roofing Experts.