Loft Conversion Specialists · All 32 Boroughs
Loft Conversion in London
Soraiz Builders designs and builds loft conversions across Greater London, covering rear dormers, hip-to-gable, L-shaped dormers, mansards and rooflights. We handle Building Control, structural calculations and Party Wall notices as part of the project. Every enquiry gets a written quote within 2 hours.
Quick Answer
A loft conversion in London costs £25,000 to £120,000+ in 2026, depending on type. A rooflight conversion runs £25,000–£45,000. A rear dormer, the most common choice on London terraces, costs £45,000–£75,000. Hip-to-gable runs £55,000–£85,000 and a mansard £70,000–£120,000+. Most rear dormers on houses fall under permitted development, but every loft conversion needs Building Regulations approval regardless.
Ranges compiled from Checkatrade, Mayfair Studio, Buildaway and Absolute Lofts 2026 London data.
Conversion Types
Which Conversion Type Suits Your London Property
The right type of conversion is decided by your roof, not your budget. Head height is the first test: you need at least 2.1 metres from the existing ceiling joists to the underside of the ridge for a usable conversion, and 2.3 metres or more to work comfortably around a staircase. Most Victorian and Edwardian terraces in London clear this. Below it, a dormer or mansard becomes necessary to create the height rather than optional.
Rooflight (Velux) conversion
Best for: lofts that already have head height
The roof structure stays as it is. Rooflights are fitted flush into the existing slope, the floor is strengthened, and the space is insulated, plastered and fitted out. The cheapest and fastest option, but only viable where the ridge height already works. Rooflights sit under Class C permitted development, which is not removed in conservation areas.
Rear dormer
Best for: terraced and semi-detached houses
A box structure projects out from the rear roof slope, creating full standing height and usable floor area across the back of the loft. The workhorse of London roof projects and the most common type we are asked to price. Usually qualifies for permitted development on a house, provided the volume allowance holds.
Hip-to-gable
Best for: semi-detached, detached, end-of-terrace
The sloping hip end of the roof is built up into a vertical gable wall, squaring off the loft and adding headroom along the side. Almost always combined with a rear dormer to gain floor area as well as height. Common on 1930s semis around Twickenham, Greenford and North Finchley.
L-shaped dormer
Best for: Victorian terraces with a rear outrigger
Two dormers meeting in an L over the main roof and the back addition. Where a terrace has a rear outrigger, this produces the largest usable space of any conversion short of a mansard, typically a double bedroom plus en-suite. Common on the Victorian stock in Islington, Holloway and Clapton.
Mansard
Best for: inner London terraces, conservation areas
The rear roof is rebuilt to a near-vertical pitch with a flat top, creating a full extra storey. The most expensive and most involved option, and the one that produces the most space. Almost always requires full planning permission and is the standard route in boroughs where dormers are refused on appearance grounds.
Shell / first-fix conversion
Best for: budget-managed or phased projects
Structure, roof works, staircase, windows and insulation completed to a weathertight, first-fix stage. Plastering, second-fix carpentry, decoration and any bathroom are left for a later phase. Typically £10,000 to £15,000 less than a full build and a practical way to spread cost across two budget years.
What every Soraiz project includes
Cost Guide
Loft Conversion Cost in London (2026)
Costs in London run between £25,000 and £120,000+ in 2026. The figures below are typical market ranges for a completed conversion including structure, staircase, insulation, electrics, plastering and decoration. These are reference ranges, not fixed Soraiz Builders prices. Every quote we issue is itemised and based on a site visit.
| Conversion type | Typical cost (London 2026) | Typical duration | Planning position |
|---|---|---|---|
| Rooflight / Velux | £25,000 – £45,000 | 4 – 6 weeks | Class C permitted development. Retained in conservation areas. |
| Rear dormer | £45,000 – £75,000 | 6 – 8 weeks | Usually permitted development on a house, within volume limits. |
| Hip-to-gable | £55,000 – £85,000 | 8 – 10 weeks | Usually permitted development. Exempt from the 20cm eaves set-back. |
| L-shaped dormer | £70,000 – £95,000 | 9 – 12 weeks | Permitted development if volume allows. Often close to the 40m³ cap. |
| Mansard | £70,000 – £120,000+ | 10 – 14 weeks | Full planning application almost always required. |
| Shell / first-fix only | £10,000 – £15,000 less | Varies | As per the conversion type chosen. |
Costs that sit outside the build figure
- En-suite bathroom: adds £8,000 to £15,000 depending on specification and how far the soil stack has to be extended.
- Structural engineer: £800 to £2,000 in London for the calculation pack Building Control requires. Every project needs one.
- Party Wall surveyor: £750 to £1,800 per surveyor per adjoining owner if a neighbour dissents. Nothing if they consent in writing.
- Planning application: from around £300 in fees plus drawings if the conversion falls outside permitted development.
- Skip hire and permits: £700 to £1,200 across a full conversion in London, including borough skip permits and trade parking.
- Contingency: allow 10 to 15%. On London’s older roof structures, opening up frequently reveals work the survey could not see.
Sources: Checkatrade 2026 cost guide, Mayfair Studio London 2026 analysis, Buildaway, Absolute Lofts, and structural engineering fee data current at August 2026. London labour runs roughly 20% above the UK national average per the Federation of Master Builders State of Trade Survey. Costing works across more than one room? Our Kitchen Renovation Cost in London (2026): Full Breakdown guide breaks down kitchen-specific figures the same way.
Want the full line-item breakdown, cost per m² and hidden costs behind these figures? See Loft Conversion Cost in London (2026).
Planning & Regulations
Do You Need Planning Permission for a Loft Conversion in London?
Most loft conversions on London houses do not need planning permission. They fall under permitted development rights in Class B of Schedule 2, Part 1 of the General Permitted Development Order. What removes those rights is a conservation area, an Article 4 direction, a listed building, or the property being a flat rather than a house. Planning permission and Building Regulations are separate approvals: you may avoid the first, but every conversion needs the second.
The conditions your conversion must meet
- Volume: up to 40m³ of additional roof space on a terraced house, 50m³ on a semi-detached or detached house.
- Ridge height: nothing may sit higher than the highest part of the existing roof.
- Principal elevation: no extension beyond the plane of the existing roof slope on any wall fronting a highway.
- Materials: similar in appearance to the existing house.
- Eaves set-back: roof extensions must be set back at least 20cm from the original eaves. Hip-to-gable conversions are exempt from this.
- Side windows: obscure-glazed and either fixed shut or set at least 1.7m above floor level.
- No verandas, balconies or raised platforms.
Required on every conversion, without exception
Three Approved Documents do most of the work here, and the trigger that changes a project from straightforward to demanding is whether the new floor sits more than 4.5 metres above ground level.
- Approved Document K (stairs): sets the staircase geometry. Alternating tread stairs are permitted where a conforming stair will not fit, serving one habitable room plus a bathroom, and need a full 2m of headroom.
- Approved Document B (fire): above 4.5m, a protected stairway with fire doors is required. Below it, an escape window of at least 0.33m² with a minimum dimension of 450mm is acceptable.
- Part L (insulation): the new roof and walls must meet current thermal standards. Building Control cannot require you to insulate the rest of the house.
- Structural: a structural engineer’s calculation pack covering floor beams, ridge beam and any dormer or gable structure.
The volume rule catches people out
The 40m³ and 50m³ allowances are cumulative over the life of the building, not per project. An earlier dormer built by a previous owner decades ago still counts against your allowance. It is also volume, not floor area, measured three-dimensionally, which is why a modest-looking rear dormer on a London terrace often consumes 25 to 35m³ and leaves very little headroom under the cap. We check this at survey stage before any design work starts.
Conservation areas: rooflights still work
In a conservation area, Class B permitted development is removed entirely, so a dormer of any size needs a full planning application. Class C, which covers rooflights, carries no such restriction. Rooflights remain permitted development provided they project no more than 150mm beyond the roof plane. If your loft has the head height to work with rooflights alone, a conservation area designation costs you nothing in planning terms. If you need a dormer for headroom, you are applying. This distinction decides the route on a large share of projects in Islington, Hackney and Twickenham.
The Party Wall etc. Act 1996
If you live in a terrace or a semi, the work almost certainly triggers the Act. Steel beams bearing into the party wall to carry the new floor or roof structure is work under Section 2, and that requires two months’ notice served on each adjoining owner before work starts. This applies whether or not you needed planning permission.
Your neighbour has 14 days to respond. Written consent means no surveyor is needed and no fees arise. Dissent, or silence, means a dispute is deemed to exist and surveyors must be appointed, with the building owner paying for both sides at £750 to £1,800 per surveyor per neighbour.
Practically, this means the Party Wall clock, not the build programme, usually governs your start date. We prepare and serve notices at least three months before the intended start so the notice period runs alongside design and Building Control rather than delaying the build.
How It Works
Our Process
The work runs on two clocks: the build programme and the approvals programme. Running them in parallel rather than in sequence is what keeps a project to schedule.
Free site visit and feasibility check
We measure head height from ceiling joists to ridge, assess the roof structure, and check whether your property sits in a conservation area or under an Article 4 direction. We also calculate how much of your permitted development volume allowance remains after any previous roof work. A written quote follows within 2 hours of the visit.
Design, structural calculations and approvals
Drawings are produced and a structural engineer prepares the calculation pack Building Control requires. Where the conversion falls outside permitted development, the planning application goes in at this stage. Party Wall notices are served in parallel so the two-month statutory period runs alongside design rather than after it.
Structural phase
Scaffolding goes up, the roof is opened, steel beams are installed and the new floor structure is built. Where a dormer or gable is part of the scheme, it is framed and made weathertight at this stage. Building Control inspects at the structural stage before anything is covered up.
First fix, second fix and finishes
Staircase installation, insulation, Electrics in London carried out by a Part P registered electrician, plumbing for any en-suite, then Plastering & Rendering in London ahead of second-fix carpentry and decoration. Fire doors and interlinked alarms are fitted to the fire strategy agreed with Building Control.
Sign-off and handover
Final Building Control inspection, then the completion certificate. That certificate matters well beyond the build: it is the document your solicitor will ask for when you sell, and its absence is one of the most common causes of delayed conveyancing on converted lofts. Electrical certification and any warranties are handed over in writing at the same time.
Where We Work
Working Across London’s Housing Stock
The right approach for a property is decided largely by when it was built. London’s roof structures fall into a handful of recognisable patterns, and each one points toward a different route. Loft work is often planned alongside wider changes to the rest of the property, which our House Renovation in London, Planned and Delivered by One Local Team service also covers.
Victorian and Edwardian terraces
The stock across Islington, Holloway, Finsbury Park, Clapton and Bethnal Green. Generous ridge heights and a rear outrigger make these the natural home of the L-shaped dormer. The complication is planning: large parts of Islington and Hackney sit within conservation areas, where dormers need a full application and mansards are often the only form the council will accept.
1930s semi-detached houses
Common around Twickenham, Greenford, North Finchley and Totteridge. Hipped roofs on these properties waste volume at the sides, which makes hip-to-gable with a rear dormer the standard approach. The 50m³ allowance for a semi gives more room to work with than a terrace, and these usually stay within permitted development.
Post-war and ex-local-authority housing
Found across Woolwich, Croydon and outer boroughs. Many of these have trussed rafter roofs, which are convertible but need the trusses cut and replaced with a new structural floor and support, adding cost over a traditional cut roof. Head height is often tighter, so a dormer becomes structural necessity rather than preference.
Flats and maisonettes
Permitted development rights do not apply to flats or maisonettes at all, so a full planning application is required regardless of size. Leasehold consent from the freeholder is a separate requirement on top of planning, and the floors and ceilings between flats count as party structures under the Act. We assess both before quoting.
FAQs
Common Questions
Direct answers to the questions London homeowners ask most before committing to a loft conversion.
Costs run £25,000 to £120,000+ in 2026 across London. A rooflight conversion runs £25,000–£45,000, a rear dormer £45,000–£75,000, hip-to-gable £55,000–£85,000, and a mansard £70,000–£120,000+. An en-suite adds £8,000–£15,000. London labour runs roughly 20% above the national average, and older roof structures frequently reveal additional work once opened up.
Usually no, if your property is a house and you stay within the volume limits. Permitted development allows 40m³ of additional roof space on a terraced house and 50m³ on a semi-detached or detached house. Conservation areas, Article 4 directions, listed buildings and flats all remove those rights. Rooflight conversions are treated separately under Class C and remain permitted even in conservation areas.
You need at least 2.1 metres measured from the existing ceiling joists to the underside of the ridge, and 2.3 metres or more to work comfortably around a staircase. Most Victorian and Edwardian terraces in London clear this. Below 2.1 metres, a dormer or mansard becomes necessary to create the height, or the ceilings on the floor below can be lowered. Building Control assesses habitable height separately under Approved Document K.
Build time runs 4 to 6 weeks for a rooflight, 6 to 8 weeks for a rear dormer, 8 to 10 weeks for hip-to-gable, and 10 to 14 weeks for a mansard. Approvals sit outside that. Party Wall notice periods are two months minimum, and a planning application takes around 8 weeks. Running approvals in parallel with design is what keeps the overall programme down.
Almost certainly, if you live in a terrace or a semi. Cutting steel beams into the party wall falls under Section 2 of the Party Wall etc. Act 1996 and requires two months’ notice to each adjoining owner. Your neighbour has 14 days to respond. Written consent costs nothing. Dissent or silence means surveyors are appointed at £750 to £1,800 per surveyor per neighbour, paid by you. Notice is required whether or not you needed planning permission.
Yes, but the route changes. Conservation area status removes Class B permitted development entirely, so any dormer needs a full planning application. Rooflights sit under Class C, which carries no conservation area restriction, and remain permitted provided they project no more than 150mm beyond the roof plane. Where a dormer is refused on appearance grounds, a mansard is often the form councils will accept instead.
Industry estimates put the uplift at around 20% of property value, with the Federation of Master Builders citing roughly that figure and some London valuations running to 20–25%. The uplift is strongest when the conversion adds a genuine double bedroom with an en-suite rather than a small study. The work also uses existing footprint, so no garden is lost, which matters on London plots.
An itemised quote should cover: drawings, structural calculations, Building Control fees, planning handling if required, Party Wall notice preparation, scaffolding, structural steelwork, staircase, insulation, electrics, plastering, second-fix carpentry and decoration. A lower quote very often excludes several of these. Ask specifically whether the structural engineer’s fee and Building Control fees are inside or outside the figure, since those two are the most commonly omitted.
Client Reviews
What London Homeowners Say About Soraiz Builders
★★★★★
There is an old saying: empty vessels make the loudest noise. Soraiz Builders’ work does the talking and it is quality. I have used a lot of contractors over the years and Hussain is by far one of the very best.
Charles · Hackney Wick, London · Plastering
★★★★★
Soraiz Builders were a pleasure to deal with. Responsive to my messages, reasonable pricing, timely for appointments, and completed the work to a good standard. I have referred them to other property owners.
Dillon · Woolwich, London · Hallway & Stairwell
★★★★★
Very good reliable builders, excellent service. Quality and reliable competitive prices. Had a re visit after 1 month of finishing work and rectified slight issues free of charge. Will use them again and would recommend to others.
Azhar · Islington, London · Full Interior & Gloss Woodwork
These reviews reflect Soraiz Builders’ wider portfolio of work across London.
Shamraiz Hussain has worked in building and renovation trades across Greater London for over seven years, completing 250+ projects across all 32 boroughs. He founded Soraiz Builders in 2019. The cost figures, regulatory detail and property guidance on this page come from direct experience on London sites alongside current published market data.
About Shamraiz HussainGet Your Loft Conversion Quote
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Send us your postcode and property type and we will arrange a free site visit to check head height, roof structure and your remaining permitted development volume. A written, itemised quote follows within 2 hours of the visit. No obligation.