Converting your attic into a functional bedroom, home office, or playroom is one of the most effective ways to add space and value to your home. It avoids the massive stamp duty and legal fees of moving, and utilizes existing roof space. A well-designed conversion can add up to 15% to 22% to your property's value.
However, loft conversions are major structural undertakings that require steel support beams, structural floor reinforcements, new staircases, and compliance with strict fire safety and insulation codes.
In this 2026 cost guide, we detail average loft conversion costs in the UK, compare different styles, outline structural components, and explain how to hire vetted builders on GetBuilder.
1. Average loft conversion costs in 2026
The total cost depends heavily on the size of your roof, the type of conversion, and the finish level. Below are typical UK cost benchmarks for 2026, covering shell-only builds (structural elements) vs. fully fitted solutions:
| Conversion Style | Shell-Only Cost | Fully Fitted Cost (inc. Plastering & Bathroom) |
|---|---|---|
| Velux (Rooflight) | £15,000 - £22,000 | £20,000 - £35,000 |
| Dormer Loft | £28,000 - £40,000 | £40,000 - £65,000 |
| Hip-to-Gable | £32,000 - £45,000 | £45,000 - £70,000 |
| Mansard Loft | £45,000 - £65,000 | £60,000 - £95,000+ |
[!TIP] London Premium: Due to access logistics, skip licensing, parking restrictions, and structural engineering fees, loft conversions in London typically cost 15% to 25% more than the national average.
2. Choosing a loft style: Velux vs. Dormer vs. Hip-to-Gable vs. Mansard
- Velux / Rooflight Conversion (Most Affordable): The cheapest style. The contractor does not alter the shape of your roof. They simply reinforce the floor, install insulation, add Velux windows flush with the roofline, and build a staircase. This requires a minimum existing headroom of 2.2m.
- Dormer Conversion (Most Popular): A dormer is a box-like structure extending out from the slope of the roof, creating flat vertical walls and a flat ceiling. This significantly increases usable headroom and floor space. It typically falls under Permitted Development rights.
- Hip-to-Gable Conversion: Used on semi-detached or detached houses with sloped sides (hipped roofs). The contractor extends the sloped side wall vertically upward to create a flat gable wall, maximizing staircase headroom and internal volume.
- Mansard Conversion (Highest Space): The contractor replaces one or both slopes of the roof with near-vertical walls (72-degree angle) and a flat roof. This creates the maximum usable space but requires full planning permission and represents the most structural work.
3. Structural breakdown of a loft budget
To understand where your money goes, a typical dormer conversion budget breaks down as follows:
- Structural Steels & Carpentry (30%): Attic joists are too weak to support a room. Roofers must lay heavy structural steel beams (RSJs) to support the new floor joists and roof load.
- Insulation & Drylining (20%): Attic spaces are cold in winter and hot in summer. Building control requires thick PIR insulation board (like Celotex or Kingspan) in rafters and walls to meet thermal codes.
- Staircase & Windows (15%): Installing a permanent staircase that complies with fire regulations (e.g. maximum 42-degree pitch) and fitting Velux or dormer windows.
- Electrical & Plumbing (15%): Extending heating lines for a new radiator, installing a shower ensuite, adding lighting circuits, and fitting smoke alarms wired to the mains on all floors.
- Plastering & Decoration (20%): Drylining walls, skimming plaster, fitting skirting boards, doors, and painting.
4. Key building regulations to know
- Headroom: You must have at least 2.0m of clear headroom over the stairs and inside the main room to pass Building Control inspection.
- Fire Safety: All doors leading to the staircase on the ground and first floor must be upgraded to FD30 fire doors to create a safe escape corridor. You must also have mains-powered, interlinked smoke alarms on every level.
- Insulation: R-value compliance for roofs requires thick insulation (typically 100mm between rafters and 50mm under rafters) to prevent heat loss.
Connect with vetted loft builders on GetBuilder
A loft conversion requires professional structural drawings, engineering calculations, and scaffolding. Doing it without Building Control sign-off is highly dangerous and makes your home unsellable.
With GetBuilder, you can easily connect with qualified local builders:
- Post your project details: Detail your property type, roof height, and target room design for free on GetBuilder.
- Match with local specialists: Connect with local builders verified for active liability insurance and loft portfolio references.
- Compare transparent quotes: Receive up to three competitive written estimates, review architect layouts, and select the right contractor with no success fees.
