A loft conversion is one of the most cost-effective ways to add space and value to your home — but the price varies enormously depending on the type of conversion, the size of your loft and where you live. Here’s a realistic breakdown of what to expect in 2026.
Loft conversion costs by type
Velux / Roof light conversion
Typical cost: £15,000–£28,000
A Velux conversion fits roof windows into the existing roof slope without adding a dormer structure. Because the roofline doesn’t change, it’s the most affordable type and usually falls within Permitted Development rights. The trade-off is that the sloping ceiling limits usable headroom on both sides of the room.
Rear dormer loft conversion
Typical cost: £25,000–£50,000
A dormer adds a box-shaped extension to the rear roof slope, creating full-height walls and dramatically more floor space. Most rear dormers are within Permitted Development rights. Adding an en-suite bathroom adds £8,000–£18,000 to the total.
Hip-to-gable loft conversion
Typical cost: £30,000–£55,000
Common on 1930s semis and detacheds, this replaces the sloping hip end of the roof with a vertical gable wall. Often combined with a rear dormer in a single project for maximum space. Usually requires planning permission.
L-shaped dormer
Typical cost: £40,000–£65,000
Two connected dormers forming an L-shape across the main roof and rear outrigger — perfect for Victorian and Edwardian terraces. Creates two or three usable rooms and typically qualifies under Permitted Development.
Mansard loft conversion
Typical cost: £45,000–£80,000+
The most spacious conversion type, replacing the rear slope with a near-vertical wall (72°) and flat top. Almost always requires planning permission. Popular on London terraces and high-value properties where maximising floor space matters most.
What affects the final cost?
- Location: London and the South East add 20–40% to labour costs compared to the Midlands and North.
- Loft size: A larger roof footprint means more materials and more finishing.
- Steelwork: Structural steel beams (RSJs) are required for most conversions and vary in size and cost.
- En-suite bathroom: The single biggest add-on — allow £8,000–£18,000 for a quality fit-out.
- Staircase: A bespoke hardwood staircase costs significantly more than a standard softwood option.
- Planning: Add £1,500–£3,000 for a planning application if required.
- Specification: Bi-fold doors, juliet balconies and high-end finishes can add £5,000–£20,000+.
Why quotes vary so much
Loft conversion quotes for the same project can vary by £10,000 or more between builders. Some of this reflects genuine differences in quality, experience and what’s included — but some of it is simply margin. Comparing three quotes from vetted local specialists is the single most effective way to ensure you’re paying a fair price.
Ready to find out what your loft conversion would cost? Use our free comparison service to receive up to 3 quotes from vetted local loft conversion specialists in your area.