Types Of Loft Conversions London

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There are a range of different types of loft conversions. Depending on the type of property, existing loft configuration and special requirements, different options are better suited to certain budgets.

Find out more about all of the different types of loft conversion in our guide. Clapham Construction is always happy to discuss your London loft conversion and help you navigate the various considerations that go into a loft conversion.

Talk to us for a free consultation and find out how to achieve your dream loft conversion.

 

London Loft Conversions: Things to Consider

There are a few basic things to consider when thinking about a loft conversion.

  1. Headroom: You need a minimum structural height of 2.2 meters from the floor joists to the roof ridge.
  2. Permissions: Permitted Development covers most houses, but flats, listed buildings, and conservation areas require full planning permission.
  3. Party Wall: You must give terraced/semi-detached neighbors two months’ notice before altering shared walls.
  4. Conversion Type: Dormers offer the best space-to-cost ratio, while Mansards are often required by councils in historic areas.
  5. Fire Safety: Adding a third story mandates interlinked mains smoke alarms and upgrading lower-floor doors to FD30 fire doors.

The Different Types of Loft Conversions

Skylight Conversion

Planning Permission: Not Usually
Required

A Skylight or ‘Velux’ loft conversion is one of the simplest conversion types to build. As the roof of the property is not altered it is normally possible to avoid planning permission. A great way to increase space at lower cost.

Two Window Dormer

Planning Permission: Usually Permitted Development

Often found on existing homes built 100 years ago and sometimes requested by the planning officers. This conversion provides a surprising amount of additional head room and can be a stylish way to add a loft conversion.

Dormer Conversion

Planning Permission: Generally Permitted Development

This is one of the most popular types of loft conversion. It provides a large amount of additional space up to 60 Cubic metres and really good head height. It also gives additional design potential such as Juliet Balcony, floor to ceiling glass and roof lights.

Hip to Gable & Rear Dormer

Planning Permission: Usually Permitted Development

As the title states, the side sloping roof has been raised , normally in brick, and allowed us the head height and structure to add a rear dormer.

Hip to Gable

Planning Permission: Generally Permitted Development

This is a simple conversion as shown in the image as all we have done is change the side sloping roof and raised this side in brick, which turns a low roof, with low head height into a workable space for any combination of conversion.

L–Shaped Mansard

Planning Permission: Strictly
Required

As with the L-Shape Dormer, the L-Shape Mansard will add a larger amount of space with multiple design options by using the roof of the rear addition. Planning permission is required for this type of work, but we can submit approval for Juliet Balconies and a terrace to really make this conversion special.

L-Shape Dormer

Planning Permission: Often Permitted Development

This type of loft conversion is built by joining two dormer builds together, utilising the rear addition. This results in a significantly larger space than other builds. This conversion gives options for more bedrooms in the new build, a terrace on the rear addition and spare rooms, studies or bathrooms.

Mansard Conversion

Planning Permission: Almost Always Required

A mansard loft conversion alters the structure of a sloping roof to an angle of 72 degrees, given a unique shape as shown. Windows are fitted into the new roof almost like small window dormers. Like Dormers the Mansard conversion is usually erected to the rear of a property , but can be constructed as a front and rear mansard (double mansard) if permitted.

Types of Loft Conversions & Planning Permissions

 

Loft Conversion Type Standard Planning Route Crucial Volume & Design Constraints Special London Considerations
Skylight / Velux Permitted Development Windows must not protrude more than 150mm from the existing roof slope. Ideal for Conservation Areas where councils strictly ban any alterations to the building’s physical silhouette.
Two Window Dormer Permitted Development (Rear only) Must remain within cumulative volume limits (40m³ for terraces, 50m³ otherwise). Frequently requested by planning officers in historic neighborhoods as a visually softer alternative to a box dormer.
Dormer Conversion Permitted Development (Rear only) Must be set back at least 20cm from the original eaves and cannot exceed the highest part of the existing roof. A Juliet balcony is allowed under PD, but a true walk-out terrace or step-out balcony always requires full planning permission.
Hip to Gable Permitted Development Materials used on the new vertical gable wall must closely match the appearance of the existing house. Only options for semi-detached or end-of-terrace homes. The volume of the gable slice counts toward your total PD allowance.
Hip to Gable & Rear Dormer Permitted Development The combined volume of both the gable extension and the rear dormer must stay under 40m³ (terrace) or 50m³ (semi/detached). Because it maxes out roof space, it frequently pushes right up against legal PD volume limits. Precise architectural calculations are vital.
L-Shape Dormer Permitted Development (Usually) Highly vulnerable to breaching the 40m³ terrace volume cap because it links two separate dormer structures together. If the flat roof of the rear extension is utilized as a roof garden or terrace, PD rights are instantly voided.
Mansard Conversion Planning Permission Required Changes the physical structure and pitch of the roof to 72 degrees, meaning it cannot technically qualify as minor roof enlargement. Despite needing full planning permission, many design-conscious London boroughs actually prefer rear Mansards over box dormers on older streets.
L-Shaped Mansard Planning Permission Required Modifies the entire main roof structure and the rear outrigger wing simultaneously. Submitting for this requires detailed design work. Highly likely to trigger intense Party Wall surveyor involvement due to shared chimney stacks and boundaries.

Three Crucial Planning Pro-Tips for London:

  • The Highway Rule: No matter the conversion type, if any part of the extension projects forward past the principal roof slope facing a public highway (the front street), it automatically requires full Planning Permission.
  • Check Article 4 Directions: Many London councils use “Article 4 Directions” to remove Permitted Development rights across entire streets or neighborhoods to preserve architectural character. Always verify with local records first.
  • Get an LDC: If building under Permitted Development, always pay the small fee to obtain a Lawful Development Certificate (LDC) from your council before starting. It is a legal document proving your build was lawful, which solicitors will demand when you eventually sell the house.

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Andy Brown
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From the initial meeting to the final finishing touch, Paul, Dangis and their team were great! We knew exactly what to expect each week, we had lots of photos and drone videos of work happening when we couldn’t see. They were full of advice and suggestions when we couldn’t visualise the end result. They left our home as clean and as tidy as they possibly could (we were living in the house as they were working around us). We are really pleased with the end result and with the building experience! Great time, fantastic work ethic and brilliant result!
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Rebecca Barrett
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We can’t thank Paul, Dangis, and the team, enough for their hard work on our house. The house is everything we had imagined and more. We increased our scope multiple times throughout the process, and the team helped us seamlessly, and were always there to answer questions and support our plans. We only have good things to say about Clapham Construction, and will definitely be recommending them to all our friends and family. Thanks again!
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Helen Stevens
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I cannot speak highly enough of Clapham Construction. Paul and Dangis were a dream to work with from start to finish. Everything was communicated so well and they provided honest, transparent and clear advice throughout; I felt supported and guided through all the decisions and they helped me make more bespoke decisions such as our windows and floor which weren’t necessarily easy! Everyone who came to work on the loft was excellent and it has all been completed to a high standard. The loft is beautiful and we just can’t believe how much space we have and how well done everything is. I would (and have!) recommend to anyone! Thank you Paul and Dangis - and we will be coming straight back to you for the next project!
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Georgia Beales
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We’ve had our dormer loft conversion for coming up to three years now and haven’t had any major issues in this time. Any minor snagging issues have been dealt with quickly by Clapham. The whole process from start to finish was seamless. All the builders were very friendly and considerate too. Will continue to recommend this company to anyone who needs a loft done and will not hesitate to use again in the future. Thank you!
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Danilo Rico
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Clapham construction service was extremely professional, the project was finished before the plan and we are so happy with our new space. Problems were resolved quickly and efficiently throughout the process. This was one of our best investment that not only added value to our property but also a significant improve of our quality of life.
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Joel Prime
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I had a loft conversion completed by Clapham Construction Service earlier this year and couldn't be happier with the results. Paul and Dangis were on site every day and kept me fully informed throughout the entire process. Their communication, professionalism, and attention to detail were outstanding. I felt completely confident in their work from start to finish. Highly recommended for anyone looking for reliable and high-quality building services.
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Jane Ansell
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We recently completed a double mansard loft conversion with Clapham Construction Service, and were very happy with the whole design and build process from start to finish. Paul and Dangis were great to work with, providing clear communication and always being available to answer questions or discuss options. Their team are also excellent, with all the trades doing a great job, very professional and respectful of the rest of our house. Inevitably with a build project there were a couple of issues that cropped up along the way, but CCS were excellent at helping resolve them. We are delighted with the final loft and the extra space, and have already recommended them to others!
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Jamie Garratt
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We have just completed a loft conversion with Clapham Construction and it was great! We are so pleased with the new loft we have in our house, but the process of working with CC was really good. They were easy to engage with from the outset, the price was competitive and the actual construction was quick and efficient. Obviously it was a major building project with all the mess and decisions you’d expect, but it was made a lot easier and less stressful working with Paul, Dangis and the team. They completed the project on time and on budget and we enjoyed working with them - that is more than almost anyone we know can say about similar projects! We’d definitely recommend them.
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Christina Ansong
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We had an exceptional experience with Clapham Construction for our loft conversion. Paul, Dangis, and the whole team were fantastic from start to finish. They transformed our attic into two beautiful loft rooms and a bathroom, exceeding our expectations with their attention to detail. The entire project was completed at an impressive speed without compromising quality. The team showed great care throughout, ensuring everything was done to the highest standard. Their service was professional, friendly, and stress-free. We’re absolutely thrilled with the results and would highly recommend Clapham Construction!
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Ayan Sengupta
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We have recently used Clapham Construction Services for loft conversion to add a bedroom and a bath in the house. We are very happy with the end-to-end experience with Paul, Dangis and the entire CCS team for high quality work done in quick time and with a very collaborative approach. Our overall project went into some unexpected blockers, but Paul and Dangis patiently helped us to resolve all the matters, kept us updated with timely communication and have been very flexible to guide us. They brought in a fantastic team to complete the work fast and in a cost-efficient manner. We will recommend CCS any day as a trusted team for home transformation projects.

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"I had a loft conversion completed by Clapham Construction Service earlier this year and couldn't be happier with the results. Paul and Dangis were on site every day and kept me fully informed throughout the entire process. Their communication, professionalism, and attention to detail were outstanding. I felt completely confident in their work from start to finish. Highly recommended for anyone looking for reliable and high-quality building services."

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Loft Conversion Types - FAQs

There are four main types of loft conversion, plus L-shaped variations that combine them. The main types are the dormer, which extends out from the roof slope and is the most popular; the hip to gable, which builds up a sloping side roof into a vertical gable; the mansard, which rebuilds the rear roof to almost vertical for the most space; and the velux or skylight conversion, which fits windows into the existing roofline with no structural change.

On many London terraces these are combined into an L-shaped dormer or L-shaped mansard for even more room.

A dormer projects a box out from the existing roof slope and is quicker and cheaper, while a mansard rebuilds the rear roof to a near vertical wall for more space and usually needs full planning permission.

A dormer can often be built under permitted development and suits most homes that want an extra bedroom without major work.

A mansard is the more involved build, but it gives the largest, most flexible floor area and a period appropriate finish, which is why many London boroughs prefer it on older streets.

If space is the priority, choose a mansard. If budget and speed matter more, a dormer is usually the better fit.

The best type depends on your roof shape, the space you want and your budget, and a free consultation will confirm it. As a rough guide: terraced houses with a rear back addition often suit an L-shaped dormer or a mansard; semi-detached and end of terrace homes are well suited to a hip to gable; most homes wanting a straightforward extra room do well with a dormer; and if you want the simplest, lowest cost option, a velux conversion works within the existing roof.

Book a free consultation and we will tell you honestly which one your property and budget point to.

Mansard conversions almost always require planning permission, while dormer, hip to gable and velux conversions can usually be built under permitted development, subject to conditions. Permitted development applies to most houses but not to flats or listed buildings, and rights can also be restricted in conservation areas. You will also need permission if the conversion exceeds the volume limits (40 cubic metres for terraces, 50 cubic metres for semis and detached homes), raises the roof height, projects beyond the principal roof slope facing a highway, or includes a terrace or raised balcony.

Read our guide to loft conversion planning permission for the detail, and always check for Article 4 directions on your street before starting.

No, you should never convert a loft without building regulations approval, even when planning permission is not needed. Building regulations are a separate legal requirement that covers the safety of the work, including the structure, fire safety, insulation, stairs and escape routes. Without a completion certificate, the conversion may raise questions about whether it meets the standards for use as a bedroom, may be unsafe, and can cause problems when you sell, as solicitors and surveyors commonly ask for evidence of compliance.

If you have inherited an unregularised conversion, you can apply to your council for a regularisation certificate. Every Clapham Construction loft conversion is built to full building regulations and signed off by building control as standard.

The 10 year rule is a planning enforcement rule: if a loft conversion was built without the planning permission it needed, the council generally cannot take ordinary enforcement action once the relevant breach has continued for 10 years, subject to exceptions. In England, from April 2024 this limit became 10 years for new breaches of planning control, after which you may be able to apply for a Lawful Development Certificate confirming the conversion is lawful. Transitional rules may apply to earlier breaches.

Two important caveats: the rule covers planning enforcement only, not building regulations, which have separate enforcement and compliance requirements, and it does not provide immunity from listed building controls. It’s a fallback, not a plan. The safe route is to build with the correct permissions from the start, and we manage that process for you.

Cost depends on the type, the size and complexity, and your property, but as an indicative guide a velux conversion is the cheapest, a mansard is the most expensive, and a dormer offers the best value for the space it adds.

Roughly, velux conversions start from around £30,000, dormer and hip to gable conversions typically fall in the region of £40,000 to £55,000, and mansard conversions usually run from around £50,000 to £70,000 or more. These are estimates only, as materials, finishes and any planning requirements affect the final figure.

For a tailored estimate try our loft price calculator, or read our full cost guide. Every price we quote is fixed and guaranteed before work begins.

A mansard conversion usually adds the most value because it creates the largest increase in usable space, effectively adding a full storey, though it also costs the most.

A well built dormer adds strong value too, especially where it includes an extra bedroom and bathroom, and a hip to gable can transform a cramped attic in a semi or end of terrace home. A velux conversion adds the least, but it is the most budget friendly way to gain space. In London, where space is at a premium, a well executed loft conversion can add considerable value, potentially around 20% depending on the property and local market. For advice on the best return for your home, book a free consultation.

There is no bad time of year for a loft conversion, because the roof is opened up in stages and made watertight quickly, so the work continues through autumn and winter. Many homeowners choose to start in spring or summer so the project is finished before Christmas and to make the most of lighter, drier days, but an autumn or winter start can sometimes mean better builder availability and shorter lead times. The bigger timing factor is planning: if your conversion needs permission, allow a couple of months for that before work can begin.

See our guide on the best time of year for a loft conversion, and note that in most cases you can stay in your home throughout.

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