A loft conversion in London typically costs between £30,000 and £100,000+ in 2026, depending on the type you choose. A simple Velux conversion starts at around £30,000; a rear dormer – the most popular option by far – runs £45,000 to £75,000; and a full mansard can reach £100,000 or more. London prices are roughly 20–30% above the national average due to higher labour rates and stricter planning conditions.

Those are honest numbers, not the “from £19,995” figures you sometimes see in adverts. We’ve been building loft conversions across London since 2010, and in this guide we’ll break down exactly what each type costs, what’s included, what pushes the price up, and where you can genuinely save money.

 

Quick Answer: London Loft Conversion Prices in 2026

Conversion type	Typical London cost (2026)	Best suited to	Build time
Velux (rooflight)	£30,000 – £45,000	Homes with good existing head height	4–6 weeks
Rear dormer	£45,000 – £75,000	Terraced and semi-detached houses	8–10 weeks
L-shaped dormer	£55,000 – £85,000	Victorian/Edwardian terraces with rear addition	10–12 weeks
Hip-to-gable (+ rear dormer)	£55,000 – £85,000	Semi-detached and end-of-terrace with hipped roofs	10–12 weeks
Mansard	£60,000 – £100,000+	Inner-London terraces, conservation areas	12–14 weeks

These figures include structural steelwork, the staircase, insulation, electrics, plastering and decoration – a finished, usable room. An en-suite bathroom adds £8,000–£15,000 on top, depending on specification.

 

What Does Each Type of Loft Conversion Involve?

Velux (rooflight) conversion – from £30,000

The simplest and cheapest option. The shape of your roof stays exactly as it is; we insulate the space, board it out, fit roof windows, add a staircase and finish everything to bedroom standard. The catch is head height – you generally need at least 2.2 metres from the ceiling joists to the ridge for the finished room to feel right. Plenty of 1930s semis have it. Many Victorian terraces don’t.

Rear dormer – £45,000 to £75,000

This is the conversion we build more than any other. A box-shaped structure extends out from the rear slope of your roof, which transforms the space – you get full standing height across most of the room and space for a proper double bedroom, often with an en-suite. Most rear dormers in London fall under permitted development, meaning no full planning application. That saves both time and money.

Hip-to-gable – £55,000 to £85,000

If you own a semi-detached or end-of-terrace house with a hipped roof (one that slopes in on the side as well as the front and back), the loft often feels uselessly small. A hip-to-gable conversion builds the sloping side up into a vertical brick gable wall, and it’s almost always combined with a rear dormer to maximise the floor area. Done together, this creates one of the biggest loft spaces possible in a semi – usually a large bedroom plus en-suite.

L-shaped dormer – £55,000 to £85,000

Common on Victorian and Edwardian terraces that have a rear addition (the back part of the house that sticks out over the kitchen). Two dormers connect in an L-shape over the main roof and the rear addition, sometimes creating enough space for two rooms. If your home has that classic London back-addition layout, this is often the best value per square metre.

Mansard – £60,000 to £100,000+

The big one. The whole rear roof slope is rebuilt at a near-vertical angle with a flat top, essentially adding a full extra storey. Mansards almost always need full planning permission, and they’re the standard choice in conservation areas where boroughs prefer them to box dormers. They cost the most, but they add the most space – and in inner London, the most value.

 

What Actually Drives the Cost Up or Down?

After fifteen years of pricing these projects, we can tell you the final figure mostly comes down to six things:

1. 1. Roof structure and head height. Older roofs sometimes need extra structural strengthening, and if head height is tight, solutions cost money.

1. 1. The bathroom. An en-suite adds £8,000–£15,000 once you account for plumbing runs, waterproofing, sanitaryware and tiling. It’s also the thing most buyers want, so it usually pays for itself in added value.

1. 1. Staircase position. A straightforward stair over the existing flight is cheap. Reworking the landing or moving walls to fit one isn’t.

1. 1. Planning route. Permitted development keeps things simple. Full planning (mansards, conservation areas, Article 4 zones) adds fees and a couple of months to the programme.

1. 1. Party walls. Terraced or semi-detached? You’ll almost certainly need party wall agreements with your neighbours. Budget £1,000–£1,500 per adjoining owner for surveyor fees.

1. Finish level. Standard finish versus underfloor heating, bespoke fitted wardrobes and high-end bathrooms can swing the total by £10,000–£20,000. If you’re thinking about built-in storage, our made-to-measure wardrobes team designs around the awkward angles that lofts always have – sloped ceilings stop being a problem when the storage is built for them.

Hidden Costs Nobody Mentions

A few items that catch homeowners out when comparing quotes:

• • Structural engineer’s calculations – required for Building Control on every loft conversion, typically £400–£900.

• • Building Control fees – usually £500–£1,000.

• • Scaffolding – sometimes quoted separately; on tight London streets a pavement licence can add cost.

• • Boiler and heating upgrades – an extra floor means extra radiators, and occasionally the existing boiler can’t cope. If yours is borderline, factor in an upgrade (something we handle in-house through our plumbing and heating team).

When you compare quotes, check whether these are included. A quote that looks £5,000 cheaper often just has £5,000 of items missing. Every quotation we issue at SBDS is fully itemised – you can see exactly what’s in and what’s not before you commit. That’s also why all our work carries a 3–5 year written warranty.

 

Is a Loft Conversion Worth It in London?

In most cases, yes – and 2026 market conditions make the case stronger. With stamp duty making moving house painfully expensive, adding a bedroom is usually cheaper than buying one. Nationwide’s long-running research puts the value added by a loft conversion with an extra bedroom and bathroom at around 15–20% of your home’s value. On a £500,000 London home, that’s £75,000–£100,000 of added value against a build cost of £50,000–£70,000.

There’s also the part that doesn’t show up in a valuation: not moving. Same street, same schools, same neighbours – one more bedroom.

One of our recent projects turned a completely unused loft into a double bedroom with a full en-suite shower room. The owners had been planning to move; the conversion cost less than their stamp duty and estate agent fees would have. You can see that project and others in our completed projects gallery.

 

How Long Does a Loft Conversion Take?

• • Velux: 4–6 weeks

• • Rear dormer: 8–10 weeks

• • Hip-to-gable or L-shaped: 10–12 weeks

• • Mansard: 12–14 weeks

Add 8–10 weeks beforehand if full planning permission is needed. One thing worth knowing: most of the structural work happens through the roof from scaffolding outside, so you can live in your home throughout the build. The disruptive part – cutting through for the staircase- usually comes in the final third of the project.

 

How to Keep the Cost Down (Without Cutting Corners)

• • Stay within permitted development if you can. A rear dormer designed within PD rules avoids planning fees and delays.

• • Keep the bathroom above existing plumbing. Stacking the new en-suite over the bathroom below shortens pipe runs and saves real money.

• • Decide your specification before work starts. Mid-project changes are the single biggest cause of budget creep – a £200 decision made on paper can cost £2,000 once walls are closed up.

• • Get an itemised, fixed quote. If a builder gives you one round number on a single sheet of paper, walk away.

If you’re weighing up a loft conversion against other ways of adding space, it’s worth comparing numbers – we’ve covered extension pricing separately, and for many London homes a kitchen extension or a loft conversion come out at similar cost but solve different problems. One adds living space, the other adds bedrooms. Some clients doing a full house renovation combine both in a single project, which usually works out cheaper than doing them two years apart.

 

Frequently Asked Questions

Q1. How much does a loft conversion cost in London in 2026?

Between £30,000 and £100,000+. A Velux conversion starts from around £30,000, a rear dormer typically costs £45,000–£75,000, and a mansard conversion ranges from £60,000–£100,000+. The final cost depends on your roof type, the size of the loft, and whether you include features such as an en-suite bathroom.

Q2. Do I need planning permission for a loft conversion?

Often, no. Most rear dormer and Velux loft conversions fall under permitted development rights. However, full planning permission is usually required for mansard conversions, most front-facing dormers, properties in conservation areas, and homes located in Article 4 areas. Regardless of the planning route, every loft conversion must comply with Building Regulations.

Q3. What’s the cheapest type of loft conversion?

A Velux (rooflight) loft conversion is generally the most affordable option, starting from around £30,000 in London. This is only suitable if your loft already has sufficient head height (approximately 2.2m or more at the ridge). If additional space is needed, a rear dormer is usually the most cost-effective solution.

Q4. How much value does a loft conversion add to a London home?

A professionally completed loft conversion can typically increase a property’s value by 15–20%, especially when it adds an extra bedroom and bathroom. In many cases, the increase in property value exceeds the cost of the conversion.

Q5. Can I live in my house during a loft conversion?

Yes. Most homeowners remain in their property throughout the project. The majority of the construction work is carried out externally using scaffolding, and the connection to your existing landing is usually completed towards the end of the build, helping to minimise disruption.

Q6. Does the price include the staircase and decoration?

Yes. Our quotations include steelwork, staircase, insulation, windows, electrics, plastering, and decoration, with every item clearly detailed. When comparing quotes from different builders, it’s important to check exactly what is included, as not all companies provide the same level of detail or complete package.

 

Thinking About Your Loft?

The honest first step is a survey, not a price list — because your roof shape decides half the answer. We offer free, no-obligation site surveys across London, and you’ll get a fully itemised fixed quote with everything in writing, backed by our 3–5 year warranty and 55+ five-star Google reviews.

Request your free loft survey → or call us on +44 7706 680618.