How much does a loft conversion cost?

A loft conversion is one of the best ways to add real, usable space to a Bristol home without losing garden or moving house. It’s also a serious spend, often the second-biggest cheque you’ll write after the mortgage. So the honest answer to “how much does it cost?” is: it depends, and anyone who gives you a firm figure over the phone without seeing your roof is guessing.

Below is a straight guide to what you should realistically expect to pay in 2026, what pushes the price up or down, and how to make sure the quote you accept is one you can actually trust.

Realistic price ranges by type

Lofts come in a few common shapes. These are broad 2026 ranges for the Bristol area, including the building work and a basic finish, but excluding VAT and big extras like a high-end bathroom. Treat them as ballparks, not promises.

Rooflight (Velux) conversion

The simplest type. You keep the existing roof shape and add windows that sit flush with the slope. No major structural changes outside, so it’s the cheapest and quickest route. Roughly £30,000–£45,000. Only works if you already have enough head height up there.

Dormer conversion

A dormer is a box-shaped extension that projects out from the rear roof slope, creating proper standing room and a flat ceiling. By far the most popular choice on Bristol’s terraced and semi-detached homes in areas like Bishopston, Southville and Horfield. Roughly £45,000–£65,000.

Hip-to-gable conversion

For semi-detached or end-of-terrace houses with a sloping (“hipped”) side roof. The sloped end is built up into a vertical gable wall to gain width and volume, often combined with a rear dormer. Roughly £55,000–£75,000.

Mansard conversion

The biggest job. The whole roof structure is rebuilt with a steep, near-vertical rear wall, giving the most space and the smartest look, common on Victorian terraces in Clifton and Redland. It almost always needs planning permission. Roughly £65,000–£90,000+.

What actually drives the cost

Two houses on the same street can come back with very different numbers. Here’s why.

Structural work. Cutting into a roof means new steel beams to carry the load and a strengthened floor to take the new room. The more steel and the trickier the access, the higher the bill.
The staircase. Fitting a safe, building-regs-compliant stair into an existing house is often the hardest part. If it eats into a bedroom below or needs a clever turn, it costs more.
An en-suite or bathroom. Lovely to have, but it means new plumbing and waste runs up through the house, plus tiling and fittings. Budget a few thousand on top, more if you want a proper rainfall-shower finish.
Access. A narrow Victorian terrace with no side return means materials and waste go through your house or get craned over the roof. That’s slower and dearer than a property with easy rear access.
Finishes. Flooring, joinery, built-in wardrobes, lighting and decoration can swing the final figure by £10,000 or more. This is the part you control most.
Heating. The new room needs to tie into your system, and an older boiler may struggle with the extra demand. It’s worth checking early; see our heating services if you’re unsure.

What a proper quote should include

A good written quote is itemised so you can see where the money goes. Look for:

Architectural drawings and the building control / structural engineer fees
All structural steel and floor strengthening
The staircase, and any making-good to the room it comes out of
Insulation, plastering, electrics, heating and plumbing
Windows, doors and the dormer cladding or roof finish
Scaffolding, skips, waste removal and clean-up
A clear payment schedule tied to stages of work, not big sums up front
What is excluded (this matters as much as what’s included)

If you’ll be building near a shared wall with a neighbour, the Party Wall Act may apply, meaning you need a formal agreement before work starts. Ask whether that’s allowed for.

Why a fixed written quote beats a cheap verbal estimate

An “estimate” is a guess that can drift upwards once the work starts. A fixed written quote is a commitment to a price for a defined scope. The difference can be tens of thousands by the end.

Be especially wary of the cheapest number. In our experience the lowest quote is often low because something has been left out, the steel, the proper insulation, the making-good, and those gaps reappear later as “extras” once you’re committed and the roof is open. A builder who has measured up, asked about your boiler and drains, and put it all in writing is usually the one who has actually thought the job through.

A sensible approach: get three quotes, make sure they cover the same scope, and judge them on detail and clarity rather than the headline figure alone.

If you’d like a straight, no-pressure conversation about your own loft, we’re happy to visit, take a proper look and give you a fixed written quote with everything itemised. You can get a free quote, see our recent work, or check the areas we cover.