Key takeaways
- A 2026 loft conversion costs from £30,000 for a simple rooflight up to around £70,000 for a mansard, according to Federation of Master Builders figures.
- Dormer conversions average £50,000 and hip-to-gable conversions average £60,000, with en-suites adding £3,000 to £7,000.
- Adding a bedroom and bathroom through a loft conversion can lift a property's value by up to 24%, Nationwide research found.
- Structural work, the staircase and finishes are the biggest cost drivers, so request an itemised quote before you commit.
- Northamptonshire homeowners usually pay close to the UK average, sometimes slightly below, so budget realistically and keep a 10% contingency.
A loft conversion in 2026 typically costs from around £30,000 for a simple rooflight conversion up to about £70,000 for a mansard, with dormers sitting around £50,000. Your final price depends on the conversion type, the structural work involved, and the finishes you choose.
If you are weighing up a loft conversion cost in 2026 and trying to compare quotes, this guide gives you clear price bands for each conversion type, explains what drives the numbers up or down, and shows how the figures apply to homeowners here in Northamptonshire. We work on loft projects across the county, so these are the questions we answer every week.
Average loft conversion cost in 2026 by type
The type of conversion is the single biggest factor in your budget. The Federation of Master Builders publishes average UK figures, and the latest breakdown (September 2025) sets out four main options.
- Rooflight (Velux) conversion: from £30,000. The most affordable route. You keep the existing roof shape and add windows set flush into the slope. This works when your loft already has enough headroom.
- Dormer conversion: around £50,000. A dormer extends out from the roof slope to create a boxy structure with vertical walls and a flat or pitched roof. It adds usable floor space and headroom, which makes it the most popular choice for UK homes.
- Hip-to-gable conversion: around £60,000. This replaces a sloping "hipped" side roof with a flat gable wall, opening up far more internal volume. It suits semi-detached and detached houses.
- Mansard conversion: around £70,000. The most substantial option. A mansard rebuilds much of the roof structure with a near-vertical rear wall, giving the largest room but the highest price.
If you are not sure which style fits your home, our guide to the types of loft conversion explained for UK homes walks through each one in plain terms.
What drives the price up or down
Two conversions of the same type can carry very different price tags. Here is where the money goes.
Structural work
The structure is usually the largest single cost. Most lofts need new floor joists and steel beams to carry the added load, and a dormer or mansard involves building out part of the roof. The more you alter the roof shape, the more labour and materials you need, which is exactly why a mansard costs more than a rooflight.
The staircase
Building Regulations require a permanent, fixed staircase to a habitable loft room. A basic softwood staircase starts from around £1,200, while a bespoke hardwood design can exceed £10,000. Where the stairs land also matters. If the only sensible position eats into a bedroom below, you may need to reconfigure the floor beneath, which adds cost.
Finishes
Plastering, flooring, lighting, heating, decoration and built-in storage all sit on top of the shell. Standard finishes keep costs down. Premium fittings, bespoke joinery and underfloor heating push them up. This is the part of the budget you have the most control over.
Additional costs for en-suites and dormers
Two extras come up in almost every loft project, so plan for them early.
- En-suite bathroom: a standard en-suite typically adds £3,000 to £7,000, depending on the fittings and how far the plumbing has to run.
- Dormer windows: if your loft starts as a rooflight conversion but you want more space, adding a dormer structure is a significant upgrade rather than a small tweak, so expect it to move your total toward the dormer price band.
Don't forget the fees that sit outside the build itself: planning (where needed), building control, a structural engineer's calculations, and a party wall agreement if you share a wall with a neighbour. These are routine on loft jobs, and a good contractor will flag them in the quote rather than spring them on you later.
How a loft conversion compares to an extension
Loft conversions tend to deliver strong value because they turn dead roof space into a proper bedroom, often with an en-suite, without taking up any garden.
Research from Nationwide, reported in October 2025, found that homeowners adding a large bedroom and bathroom through a loft conversion or extension could increase their property's value by up to 24%. You can read the Nationwide findings via The Intermediary for the full detail.
A loft conversion and a ground-floor extension solve different problems. A loft is the natural choice when you need another bedroom and bathroom and want to keep your outdoor space. An extension makes more sense when you want to enlarge a kitchen or living area at ground level. If you are torn between the two, compare the numbers in our guide to how much a house extension costs in 2026.
Tips to budget wisely for your loft project
A loft conversion is a big spend, so a few sensible habits protect your money and your sanity.
- Keep a contingency. Set aside at least 10% of the build cost for surprises. Older roofs in particular can hide issues you only find once work starts.
- Get an itemised quote. A proper quote breaks down structure, staircase, windows, finishes and fees separately. Vague lump-sum figures make it impossible to compare builders fairly.
- Decide your finishes early. Choosing fittings before work begins avoids costly mid-build changes and keeps the schedule on track.
- Check the regulations. Most loft conversions fall under permitted development, but not all. Confirm whether you need planning permission before you commit.
- Use a reputable, local contractor. A builder who knows local properties and building control will price the job accurately and avoid nasty mid-project surprises.
Price guidance for Northamptonshire homeowners
Northamptonshire sits in the East Midlands, where loft conversion prices usually land close to the UK average, and sometimes a little below it. In practice, that means a dormer conversion for a typical Northampton home often falls within, or just under, the national £50,000 band, while a straightforward rooflight job can come in lower.
Because so much depends on your specific roof, headroom and the finishes you choose, the only way to get an accurate number is a site visit and a written quote. At AAS Group, we survey your loft, explain which conversion type suits the property, and give you a clear, itemised price before any work begins. We handle the structural work, staircase, windows and finishes as one managed project, so you deal with a single trusted team from plot to finished room. #Construction #Northampton
Frequently asked questions
How much does a loft conversion cost in 2026?
UK averages in 2026 run from about £30,000 for a rooflight conversion to around £70,000 for a mansard, with dormers at roughly £50,000 and hip-to-gable conversions around £60,000, based on Federation of Master Builders figures.
Does a loft conversion add value to my home?
Yes. Nationwide research reported in October 2025 found that adding a bedroom and bathroom through a loft conversion or extension could raise a property's value by up to 24%, though the exact uplift depends on your home and local market.
Do I need planning permission for a loft conversion?
Many loft conversions fall under permitted development, but some do not, especially mansards or homes in conservation areas. Always confirm before starting work.
How long does a loft conversion take?
Most conversions take several weeks to a few months, depending on the type and complexity. A rooflight conversion is usually the quickest, while a mansard takes the longest.
Planning a loft conversion in Northampton?
Get an accurate, itemised quote based on your actual roof rather than a rough online average. Contact AAS Group for a free survey, and we will talk you through the right conversion type, a realistic budget, and the full process from start to finish.
