Guide · Loft Conversions

Loft Conversion Cost UK 2026: Full Price Guide

Loft conversions have a wide price range — anywhere from £30,000 for a basic Velux up to £90,000+ for a mansard. Here's what each type actually costs in 2026 and what drives the variation on real Hertfordshire jobs.

Last updated: May 2026 · By Jamie Pocock

Quick Answer

Cost by conversion type (2026)

Velux loft conversion (£30,000–£45,000)

Roof space converted with no change to roof shape — Velux skylight windows let light in and the existing roof line stays. Cheapest, simplest, fastest (typically 5–7 weeks). Suits roofs with adequate existing head height (1.9m+ at the apex). Often permitted development without planning permission.

Dormer loft conversion (£45,000–£65,000)

Box-shaped dormer added to the rear (or side) of the roof to create full standing height across more of the floor area. The most popular type by volume — adds significantly more usable space than a Velux for a moderate price uplift. 8–10 weeks typical. Permitted development in many cases (rear dormers under permitted size).

Hip-to-gable loft conversion (£55,000–£80,000)

The hipped end of the roof is rebuilt as a vertical gable wall, creating significantly more internal volume. Often combined with a rear dormer ("hip-to-gable plus rear dormer") for maximum space. Suits hipped semis and detached homes. 10–14 weeks typical. Usually requires planning permission.

Mansard loft conversion (£65,000–£90,000+)

Most expensive and most space-creating. The roof is essentially rebuilt with near-vertical sides and a flat top, creating a full additional storey. Common in London and conservation areas. Always requires planning permission. 12–16 weeks typical.

What's normally included in those figures

• Structural works (steel beams, new floor joists, dormer framing)
• Insulation to current Part L (typically 100–150mm PIR plus 50mm internal)
• Roof covering, lead flashings, weather detailing
• New stairs (usually within existing landing footprint)
• Plastering, decorating ready (mist coat included; final paint usually not)
• Electrics (1st and 2nd fix), heating extension, smoke and heat detection
• Fire-rated doors on landings (Part B compliance)
• Velux skylights as designed (typically 2–4 included)
• Building Control submission, inspections and final sign-off
• Insurance-backed workmanship guarantee

See our loft conversion service page for full scope detail and our dormer vs Velux comparison for choosing between the two simpler types.

What pushes the price up

• Bathroom or en-suite: +£6,000–£12,000 depending on spec.
• Architect and structural engineer: £2,500–£5,500 typical (often paid separately upfront).
• Planning permission: £258 application fee plus possible drawings revisions.
• Party Wall Act notices and surveyor: £1,200–£3,500 if works affect a shared wall.
• Premium fittings: oak doors, designer skylights, bespoke joinery — variable, easy to add £5,000–£15,000.
• Steel and timber prices: have stabilised since 2023 but remain 20–30% above 2019 levels.

Type	Cost (2026)	Floor area added	Time	Planning
Velux	£30k–£45k	15–25 m²	5–7 wks	Usually PD
Rear dormer	£45k–£65k	20–35 m²	8–10 wks	Often PD
Hip-to-gable + dormer	£55k–£80k	30–45 m²	10–14 wks	Planning
Mansard	£65k–£90k+	35–50+ m²	12–16 wks	Planning

Direct cost-per-m² comparison: Velux £1,400–£2,000/m², dormer £1,600–£2,200/m², hip-to-gable £1,650–£2,200/m², mansard £1,800–£2,400/m². Mansards cost more per m² because the structural rebuild is significantly larger.

Architect and engineer fees. Often quoted separately to the build cost. Budget £2,500–£5,500 for typical residential drawings, structural calcs and planning submission. Reputable builders will recommend an architect early, not after they've quoted.

Decoration and flooring. Most build quotes include plaster ready for paint, but not the final paint, flooring, curtains or furniture. Budget another £3,000–£8,000 for these — not insignificant on a £45,000 build.

Heating system upgrade. Adding a bathroom and 2 radiators upstairs may push your existing boiler past its capacity. Boiler upgrade cost £2,000–£3,500 — worth assessing during design rather than discovering at second-fix.

Property value uplift. A well-executed loft conversion typically adds 15–20% to property value in our area — frequently more than its cost. The investment case is good, but only if the work is done to a standard surveyors and buyers will accept.

VAT. Standard rate (20%) applies on most loft conversions. Reduced rate (5%) sometimes available for properties unoccupied 2+ years or for certain conversions — confirm with your contractor early. We discuss VAT position openly during quoting.

About the Author

Jamie Pocock — Owner & Lead Contractor

Jamie has 25 years' hands-on experience in roofing and building across Hertfordshire and Essex. He runs every J&Co Contractors project personally — from quote to completion — and writes these guides from real on-the-tools knowledge of what works, what doesn't, and what costs what in 2026.

• 25 years' hands-on roofing and building experience
• CRC Certified Roofer — self-certifies under Building Regs
• SafeContractor approved
• Insurance-backed workmanship guarantee on every job