LOFT CONVERSION COSTS · LONDON · 2026
Loft Conversion Cost in London
A London loft conversion typically ranges from £22,500 – £36,000 excluding VAT for a rooflight or Velux conversion to £54,000 – £85,500 excluding VAT for a mansard.
A common rear dormer conversion is approximately £40,000 – £63,000 excluding VAT, depending on the property, roof structure, access, design and required finish.
Indicative 2026 guidance only. Prices exclude VAT. A site assessment, agreed design and detailed specification are required before Growchance can provide a project quotation.
LOFT CONVERSION PRICE COMPARISON
How much does each type of loft conversion cost?
The conversion type affects how much new structure, roofing, weatherproofing and internal work is required. A rooflight conversion normally retains more of the existing roof, while dormer, hip-to-gable and mansard schemes involve progressively greater structural change.
These are Growchance’s indicative 2026 London ranges for the main structural conversion and standard internal finishing. The final quotation depends on the property, design, access and specification.
The ranges cover the main structural conversion and standard internal finishing, subject to the final quotation. Professional and statutory fees, premium products and other separately specified work are not included automatically.
This is a separate standard en-suite allowance and is not included in the base conversion ranges above.
Areas and programmes are indicative. Roof condition, structural design, access, approvals, hidden defects, service upgrades and the selected finish can alter both cost and timescale.
UNDERSTANDING THE QUOTED SCOPE
What is included in the main loft-conversion price?
The published ranges represent the main structural conversion and a standard internal finish. They are intended to describe a complete construction scope rather than the cost of forming the roof structure alone.
The exact inclusions must still be confirmed in the project-specific quotation and specification.
Preparation and protection
Site setup, working-area protection, standard access planning and waste arrangements required for the agreed conversion.
Standard scaffolding
Standard scaffolding needed to provide suitable external access for the principal roof and structural work.
Structural floor and steelwork
The new floor structure, specified steelwork, supporting elements and associated structural construction for the conversion.
Roof construction
The principal dormer or roof alterations, structural carpentry and standard external roof finish required by the agreed design.
Weatherproofing and insulation
Standard insulation, roof coverings and weatherproofing work forming part of the new loft envelope.
Windows and staircase
Standard roof windows or agreed dormer windows, together with the staircase and opening required to connect the new level.
Internal construction
Plasterboard, plastering, standard internal doors and the principal joinery required to form the new loft rooms.
Services and completion
Standard electrical work, basic lighting, heating connections, fire protection, making good, decorating and final clearance.
Construction requirements vary between properties. The quotation should identify the agreed structural work, products, services, finishing level and any work priced separately before the project begins.
BUDGET ITEMS TO CHECK SEPARATELY
What is not included in the main guide price?
The headline ranges cover the main conversion and a standard internal finish. They do not automatically include every professional fee, approval, product upgrade or additional room specification.
A useful quotation should clearly distinguish the principal construction cost from allowances, third-party charges and optional improvements.
VAT
All prices in this guide exclude VAT. The applicable VAT must be added when establishing the total project budget.
Professional services
Architectural design, measured surveys, structural engineering, calculations and specialist professional advice are separate unless expressly included.
Approvals and statutory fees
Planning, lawful-development, Building Control and other applicable statutory charges are not included in the principal ranges.
Party wall matters
Party wall surveyor fees and adjoining-owner matters are assessed separately where the proposed work engages the relevant procedures.
Premium finishes and products
Bespoke joinery, premium flooring, upgraded windows, specialist finishes and higher-specification products require separate allowances.
Additional structural or service work
Hidden defects, unusual steelwork, drainage alterations, major service upgrades or work beyond the agreed loft scope may change the price.
Specialist design features
Juliet balconies, complex glazing, extensive fitted storage and other bespoke architectural features are priced separately.
Exceptional property conditions
Asbestos, restricted access, substantial roof repairs, forming falls, lowering ceilings or foundation work require individual assessment.
A lower headline figure may exclude design, approvals, scaffolding, steelwork, windows, staircase work, fire protection, services or finishing. Confirm every inclusion and exclusion before comparing project prices.
LONDON PROPERTY TYPES
How does the type of house affect loft-conversion cost?
Property type can affect the suitable conversion, available roof volume, structural design, access and amount of work needed almost as much as the proposed loft layout.
A rear dormer on a Victorian terrace should not be priced in the same way as a hip-to-gable conversion on a 1930s semi-detached house. These ranges provide more useful property-specific starting points.
Victorian mid-terrace
Traditional London roofVictorian terraces may have chimney structures, party walls on both sides, restricted access and a rear outrigger. The roof form can make a rear or L-shaped dormer particularly effective.
- Rooflight only £24,000 – £36,000
- Standard rear dormer £40,000 – £63,000
- Large rear dormer £49,000 – £70,000
- L-shaped dormer £50,000 – £77,000
- Mansard £55,000 – £86,000
Edwardian house
Terrace or semi-detachedEdwardian houses can offer wider proportions, but the correct conversion still depends on whether the property is terraced or has a hipped side roof.
- Terrace · rear dormer £42,000 – £65,000
- Terrace · L-shaped dormer £52,000 – £80,000
- Terrace · mansard £57,000 – £88,000
- Semi · hip-to-gable + dormer £54,000 – £78,000
1930s semi-detached
Frequently built with a hipped roofThe sloping side of a typical hipped roof reduces usable internal width. A hip-to-gable alteration combined with a rear dormer is often the strongest space-producing solution.
- Rooflight conversion £25,000 – £38,000
- Rear dormer only £42,000 – £62,000
- Hip-to-gable only £43,000 – £63,000
- Hip-to-gable + rear dormer £52,000 – £77,000
- Large or complex combination £65,000 – £85,000+
End-of-terrace
One adjoining propertyAn end terrace may provide improved side access and only one direct party wall, but many have a hipped roof requiring more substantial alteration to create usable width.
- Hip-to-gable + rear dormer £50,000 – £73,000
Detached house
Larger roofs and conversion areasDetached houses can avoid some party-wall complications, but wider roofs, two hipped sides, larger dormers and more extensive structural work can increase the overall project cost.
- Straightforward conversion £48,000 – £70,000
- Large hip-to-gable/dormer £58,000 – £85,000
- Major structural conversion £70,000 – £95,000+
Bungalow
Large roof footprintBungalows can provide generous roof area but may need significant structural and roof alteration to achieve suitable headroom, circulation and a practical staircase.
- Rooflight conversion £27,000 – £43,000
- Standard dormer conversion £41,000 – £63,000
- Large dormer/chalet conversion £50,000 – £76,000
- Major roof reconstruction £63,000 – £90,000+
Modern house with a trussed roof
Additional structural designMany newer houses use prefabricated roof trusses. These members cannot simply be removed to clear the loft. The roof structure must be redesigned so the loads are transferred through new structural steelwork or timber supports before existing truss members are altered.
Prices exclude VAT. The property label alone cannot establish the final cost. Roof condition, dimensions, structural design, staircase position, access, planning constraints, services and specification must still be assessed for the individual house.
LOFT CONVERSION COST PER M²
Is cost per square metre a reliable way to budget?
A square-metre rate can provide a useful secondary check, but it should not be the main method used to price a loft conversion.
Every conversion contains substantial fixed structural, access and compliance costs. A smaller loft therefore does not necessarily cost proportionally less than a larger one.
Roof structure, conversion type, staircase design, steelwork, scaff;]/ding, fire protection and services can make two lofts of the same floor area cost very different amounts.
Rooflight conversion
£1,500 – £2,100/m²A secondary budget check where the existing roof form is substantially retained.
Rear dormer
£1,500 – £2,100/m²The final figure depends on dormer size, structural design and finishing specification.
Hip-to-gable
£1,875 – £2,250/m²Reflects the additional work involved in rebuilding the hipped side of the roof.
L-shaped dormer
£1,875 – £2,250/m²Typically involves conversion work across both the main roof and rear addition.
Mansard conversion
£2,625 – £3,375/m²A more substantial reconstruction of the roof with increased structural and planning complexity.
- Staircase and structural floor opening
- Steelwork and structural strengthening
- Scaffolding and external access
- Fire protection and Building Regulations work
- Roof construction and weatherproofing
- Windows, insulation and ventilation
- Electrical and heating alterations
- Design, approvals and inspections
All rates are indicative Growchance planning figures excluding VAT. They should be considered alongside the conversion-type and property-specific ranges, not used independently to calculate a final project price.
LONDON LOCATION AND ACCESS
Does the London location affect loft-conversion cost?
Location can affect the cost, but a loft conversion should not be priced from the borough name alone.
The important differences are usually access, parking, scaffolding, property type, planning constraints and specification rather than the postcode itself.
First identify the appropriate conversion and property-type range. The location and site conditions can then indicate whether the project is likely to remain near that range or require an additional allowance.
Outer London with straightforward access
Base rangeA suitable starting point where access, parking, scaffolding and material handling are relatively straightforward.
Bromley, Croydon, Sutton, Enfield, Harrow and parts of Barnet and Ealing.
Typical inner-London conditions
+5 – 8%Tighter access, parking controls, more complex logistics and additional protection can increase labour and delivery costs.
Controlled parking, restricted deliveries, narrow access and occupied adjoining properties.
Premium or difficult-access locations
+5 – 10%Higher specifications and more restricted working conditions can move the project above the normal starting range.
Chiswick, Richmond, Wimbledon, Clapham, Fulham, Hammersmith, Islington, Highgate and Hampstead.
Severely constrained or complex sites
+10 – 20%+Major access limitations, conservation requirements, premium specifications or unusually complex logistics can require a more substantial allowance.
Prime central locations and highly constrained or conservation-sensitive properties.
- Rear, side and internal access
- Parking and delivery restrictions
- Scaffolding configuration
- Waste-removal arrangements
- Conservation or planning constraints
- Property value and finish specification
- Neighbour and party-wall considerations
- Working hours or site restrictions
- Material lifting and storage space
Percentage adjustments are indicative planning allowances, not automatic postcode charges. Every project must be assessed from its actual property, access, design and working conditions. All guide prices exclude VAT.
WHAT CHANGES THE FINAL BUDGET?
The main factors affecting loft-conversion cost.
Conversion type and property style provide a useful starting range, but the final budget must be based on the actual roof, proposed layout and required construction.
These factors explain why apparently similar London loft conversions can receive substantially different quotations.
Existing roof structure
Roof height, pitch, span, timber arrangement, chimney structures and whether the roof uses traditional rafters or prefabricated trusses determine how much structural alteration is required.
Conversion size and shape
A rooflight conversion retains more of the existing roof. Dormers, hip-to-gable alterations, L-shaped designs and mansards require progressively more new structure and external construction.
Staircase position
The staircase must provide practical access while working with the existing landing, headroom and room layout. A complex opening or bespoke staircase increases design, structural and joinery work.
Access and scaffolding
Restricted rear access, controlled parking, difficult material handling and complex scaffolding arrangements can increase labour, delivery and waste-removal costs.
En-suite and services
Adding a bathroom introduces drainage, plumbing, water-pressure, ventilation, waterproofing, electrical and finishing requirements. Service routes can materially affect feasibility and price.
Internal specification
Flooring, windows, doors, fitted storage, lighting, heating, decorating and bathroom products determine whether the project remains within a standard finish or moves into a premium scope.
Compliance work
Floor strength, roof stability, fire protection, stairs, insulation, sound separation and ventilation must be addressed through the applicable Building Regulations process.
Hidden conditions
Damaged roof timbers, unsuitable supporting walls, previous alterations, asbestos or unexpected service routes may only become clear after surveys or controlled opening-up.
Design and planning constraints
Conservation requirements, roof-volume limits, overlooking concerns and the need for planning permission can affect the conversion form, materials, design work and programme.
- Conversion type and proposed floor area
- Structural design and steelwork
- Scaffolding, access and waste removal
- Staircase and internal layout
- Windows, roofing and insulation
- Electrical, heating and ventilation work
- Fire-protection and compliance work
- Internal finish and excluded products
One quotation may cover the main structure only, while another includes the staircase, windows, services, plastering and decoration. Confirm inclusions, exclusions, VAT and provisional allowances before deciding which figure is genuinely lower.
PROFESSIONAL AND STATUTORY COSTS
Which design and approval costs should be budgeted separately?
The main conversion ranges do not automatically include every professional service, statutory charge or neighbour-related cost.
The required route depends on the property and proposed conversion. These items should be identified before the construction quotation is treated as the complete project budget.
Architectural design and surveys
Drawings may be required to establish the proposed layout, roof form, staircase, windows, external appearance and information needed for planning or construction.
Measured surveys and more detailed design work can be required for complex properties or proposals.
Obtain a project-specific professional feeStructural engineering
The engineer assesses the loads and specifies the structural floor, steel beams, connections and supporting construction required by the conversion.
A trussed roof, unusual spans or complex existing alterations may require additional structural input.
Separate unless expressly includedPlanning or lawful-development application
Some loft conversions may fall within permitted development, while others require planning permission because of their size, form, location or property restrictions.
A lawful-development application may also be considered where formal confirmation of permitted-development status is appropriate.
Application and preparation costs assessed separatelyBuilding Regulations and inspections
Converting a loft into habitable accommodation requires Building Regulations compliance. Relevant matters include structural stability, fire safety, stairs, insulation, ventilation and sound separation.
The submission, review and inspection route should be confirmed for the individual project.
Building Control charges budgeted separatelyParty wall procedures
Party wall matters may arise where structural work affects a party wall or adjoining property. The applicable process depends on the design and relationship with neighbouring owners.
Any surveyor appointments, notices or awards should be allowed for separately where required.
Do not assume party-wall costs are includedOther property permissions
Listed-building consent, conservation requirements, restrictive covenants, freeholder approval or other property-specific permissions may apply independently of planning and Building Regulations.
The property’s legal and planning position should be checked before the final scope is agreed.
Specialist advice may be necessaryThe project scope should establish which drawings, calculations, permissions and inspections are required and whether Growchance will coordinate any agreed professional or approval stages alongside the construction work.
This section provides general budgeting guidance rather than planning, structural or legal advice. Requirements and fees must be confirmed for the individual property and proposed conversion.
LOFT EN-SUITE AND CONNECTED SERVICES
How much should you allow for a loft en-suite?
An en-suite can make the new loft more useful, but it adds a separate group of plumbing, drainage, ventilation, waterproofing and finishing costs.
Growchance therefore treats the en-suite as a separate allowance rather than hiding it inside the main loft-conversion price.
- Long or difficult waste-pipe routes
- Drainage alterations below the loft
- Water-pressure or hot-water upgrades
- Forming a wet-room floor or falls
- Premium sanitaryware and brassware
- Large-format or specialist tiling
- Bespoke shower screens or storage
- Additional structural floor work
- Complex ventilation arrangements
The en-suite position should be considered alongside headroom, staircase placement, structural supports, drainage and the rooms below. A visually convenient position is not always the most practical or cost-effective service arrangement.
LOFT CONVERSION TIMESCALES
How long does a loft conversion take?
A straightforward rooflight conversion may take approximately 4 – 6 weeks, while a structurally involved mansard may require approximately 12 – 16 weeks.
These periods describe the indicative construction programme. Design, permissions, structural information and pre-construction planning take place before the main building work begins.
- Site preparation, protection and scaffolding
- Structural floor, steelwork and temporary protection
- Roof alteration, dormer construction and weatherproofing
- Windows, insulation and staircase installation
- Services, fire protection, plastering and joinery
- Finishing, applicable inspections and practical completion
Complex structural details, restricted access, specialist products, poor weather during exposed roof work, hidden defects, design changes, service upgrades and delayed inspections or product deliveries can all affect the completion date.
Programmes are indicative and relate to the principal construction period. They are not guaranteed completion dates and exclude the time required for design, approvals and pre-construction preparation.
BUDGET CONTROL
How should you compare loft-conversion quotations?
Two quotations can show very different totals because they cover different work. The headline amount is meaningful only when the scope, allowances, exclusions and VAT treatment are clear.
Compare each quotation against the same design and specification, then identify any unpriced or provisional work that may change the eventual project cost.
Confirm the VAT position
The Growchance ranges in this guide exclude VAT. Check whether every contractor’s headline total includes or excludes VAT before comparing the figures.
Separate fixed prices and allowances
Identify which items are firmly specified and which remain provisional allowances dependent on final design, product selection or opening-up.
Check every exclusion
Design fees, approvals, party-wall matters, bathroom products, flooring, decoration and service upgrades can create substantial additional costs when omitted.
- Approved drawings and structural information
- Scaffolding, protection and access arrangements
- Structural floor, steelwork and roof construction
- Roof coverings, insulation and weatherproofing
- Windows, staircase and internal room layout
- Fire-safety and Building Regulations work
- Electrical, heating, plumbing and ventilation
- Plastering, joinery, flooring and decoration
- Bathroom products and en-suite installation
- Waste removal, cleaning and practical completion
- Professional, statutory and inspection charges
- VAT, payment stages and quotation validity
Older London roofs can contain hidden defects, previous alterations or unsuitable supporting construction that cannot always be confirmed from a visual inspection alone.
The appropriate contingency should reflect the surveys already completed, the age and condition of the property and how much uncertainty remains before work starts. It should not be used to hide known work that ought to be included in the quotation.
This checklist supports budget comparison but does not replace a project-specific design, specification, contract or professional advice.
PREPARE A MORE USEFUL ENQUIRY
What should you send for an initial loft-conversion review?
The guide ranges provide an early budgeting reference. A more useful project discussion begins with information about the actual property, roof and space you want to create.
You do not need to have every drawing before contacting Growchance, but the available details help us identify the appropriate next step.
Property address and type
Send the London postcode and tell us whether the property is terraced, end-of-terrace, semi-detached, detached or a bungalow.
Photographs of the roof and loft
Include clear exterior roof photographs and internal loft images showing the ridge, rafters, chimney structures, tanks and available space.
Approximate measurements
Provide the available loft length, width and approximate vertical height from the existing ceiling joists to the ridge where known.
Rooms you want to create
Explain whether the proposed loft should provide a bedroom, bedrooms, an office, storage, an en-suite or another usable layout.
Existing drawings or information
Share any floor plans, architectural drawings, structural information, planning history or previous survey material already available.
Budget and preferred timescale
Tell us the working budget, preferred start period and whether the property will remain occupied during the proposed work.
Photographs and approximate measurements help establish the starting point but cannot confirm the final structure, planning route, Building Regulations requirements, project price or construction programme.
LOFT CONVERSION COST QUESTIONS
Useful answers before setting your budget.
These answers explain the main cost, scope and programme considerations. The final price still depends on an assessment of the individual property and proposed conversion.
Discuss Your Loft Conversion01 How much does a loft conversion cost in London?
Growchance’s indicative 2026 London ranges start at approximately £22,500 – £36,000 excluding VAT for a rooflight or Velux conversion. A typical rear dormer is approximately £40,000 – £63,000 excluding VAT, while a mansard is approximately £54,000 – £85,500 excluding VAT.
These figures cover the main structural conversion and a standard internal finish. Professional and statutory costs and any en-suite are separate unless expressly included.
02 What is the cheapest type of loft conversion?
A rooflight or Velux conversion is generally the lowest-cost option because the external roof shape is substantially retained. It is only practical where the existing roof provides enough height and usable space without a dormer or major roof alteration.
03 How much does a rear dormer loft conversion cost?
A standard London rear dormer is approximately £40,000 – £63,000 excluding VAT for around 25 – 35 m² of usable area. A wider rear dormer may be approximately £49,500 – £76,500 excluding VAT.
Property type, roof structure, dormer dimensions, staircase, access, services and the required finish determine where the project sits within or beyond those ranges.
04 How much does a loft conversion cost per square metre?
Growchance’s secondary planning ranges are approximately £1,500 – £2,100/m² excluding VAT for rooflight and rear-dormer conversions, rising to approximately £2,625 – £3,375/m² excluding VAT for mansards.
Cost per square metre should not be used by itself because structural floors, stairs, steelwork, scaffolding and fire-safety work create substantial fixed costs.
05 Does a Victorian house cost more to convert?
Not automatically. Victorian properties may contain chimney structures, party walls, restricted access and a rear outrigger, but they can also have roof forms well suited to rear or L-shaped dormers.
A Victorian mid-terrace rear dormer is approximately £40,000 – £63,000 excluding VAT, while an L-shaped dormer is approximately £50,000 – £77,000 excluding VAT.
06 How much extra should I allow for a loft en-suite?
Growchance’s standard loft en-suite allowance is approximately £6,500 – £11,500 excluding VAT. It is separate from the main conversion price.
Complex drainage, water-pressure upgrades, premium products, extensive tiling or a more demanding layout can increase the final en-suite cost.
07 Are design and approval fees included?
Not in the headline ranges unless expressly stated. Architectural design, structural engineering, planning or lawful-development applications, Building Control and party-wall costs should be identified separately.
08 Do all loft conversions need planning permission?
No. Some house loft conversions may fall within permitted development, subject to the applicable limits and conditions. Other proposals require planning permission because of their form, size, location, property restrictions or planning history.
Building Regulations apply separately when a loft is converted into habitable accommodation.
09 How long does a loft conversion take?
Indicative construction programmes range from approximately 4 – 6 weeks for a rooflight conversion to approximately 12 – 16 weeks for a mansard. A typical rear dormer is approximately 8 – 12 weeks.
Design, approvals and pre-construction preparation take place before the principal building programme begins.
10 What should a loft-conversion quotation include?
It should clearly identify the structural work, scaffolding, roofing, windows, staircase, insulation, fire-protection work, electrical and heating alterations, plastering, joinery, finishing, waste removal and inspection arrangements included in the scope.
It should also state the VAT position, professional and statutory exclusions, product allowances and any items that remain provisional.
DISCUSS YOUR LOFT CONVERSION
Tell us about your property and the loft space you want to create.
Share the available details and Growchance will review your enquiry. We can then discuss the likely conversion route, information still required and whether an assessment or site visit is the appropriate next step.
London postcode, house type, approximate age and whether the property is freehold, leasehold or listed if known.
Preferred conversion type, rooms required, approximate dimensions and whether you want an en-suite.
Mention any photographs, floor plans, architectural drawings, structural information or planning history already available.
Your working budget, preferred timescale and the level of internal finish you are considering.
Submitting an enquiry does not create a contract, confirm structural feasibility or guarantee availability. Final scope, programme and price are agreed separately after the necessary assessment and project information.