01
What it is
A dormer loft conversion is a flat-roofed box-like extension built out from the rear slope of your existing roof, creating vertical walls and full standing headroom across the new room.
Dormer Loft Conversions in London
A dormer loft conversion is the most popular way to add a bedroom and en-suite to a London terrace.
It gives you full standing headroom across the room, big windows for natural light, and on most houses it doesn't need planning permission.
We design and build dormer conversions across London with everything handled in-house, from feasibility through to final snagging.
- Planning
- Usually permitted development
- On site
- 8–10 weeks
- Best for
- Victorian and Edwardian terraces with a mid-pitch rear roof
What you actually need to know
02
How long
Around 8–10 weeks on site, with the full process taking roughly 16–22 weeks from your first call to handover.
03
Planning
Usually permitted development on houses (Lawful Development Certificate and Building Control sign-off still required). Always required for flats, front dormers and conservation areas.
04
One team, start to finish
A site manager you know by name. Weekly photo updates by WhatsApp. The same trade teams we've worked with for over seven years. No rotating subcontractors, no agency labour walking in and out.
Recent dormer conversions in South & West London
Each project is labelled with the time on site, the final price and the council that covered it.
Englewood Road, Clapham SW4
Rear dormer adding a master bedroom and en-suite to a Victorian end-of-terrace.
- Dormer
- 9 weeks
- £64k
- Wandsworth Council
Ravenswood Road, Balham SW12
Rear dormer with double bedroom, fitted wardrobes and walk-in shower room on a Victorian mid-terrace.
- Dormer
- 10 weeks
- £68k
- Wandsworth Council
Crieff Road, Wandsworth SW18
Rear dormer creating a teenage bedroom suite on an Edwardian end-of-terrace.
- Dormer
- 9 weeks
- £61k
- Wandsworth Council
Pirbright Road, Southfields SW18
Rear dormer with home office and small en-suite on a 1930s semi.
- Dormer
- 8 weeks
- £56k
- Wandsworth Council
Bushwood Road, Chiswick W4
Rear dormer adding a guest bedroom and shower room on a Victorian terrace.
- Dormer
- 9 weeks
- £67k
- Hounslow Council
Cromer Villas Road, Wandsworth SW18
Rear dormer with master bedroom, walk-in wardrobe and en-suite on an Edwardian terrace.
- Dormer
- 10 weeks
- £69k
- Wandsworth Council
Is your house suitable for a dormer loft conversion?
Good fit if you have:
- A Victorian, Edwardian, 1920s or 1930s terrace, end-of-terrace or semi-detached
- An existing ridge height of 2.3m or more (we measure this at the survey)
- A rear roof slope that runs straight front-to-back (no awkward kinks or extra hipped corners)
- Neighbours on one or both sides who already have rear dormers, which is a strong planning signal
- No conservation area restriction on the rear elevation
- A bathroom or soil stack on the floor below the loft, which keeps the new en-suite plumbing run short
Probably not the right type if:
- Your property is a flat or maisonette. Dormers there always need full planning, and a Velux conversion is usually the better route
- Your ridge height is below 2.3m. A Mansard rebuilds the rear roof and creates the headroom you need
- Your rear elevation sits in a conservation area where rear dormers are restricted. Again, a Mansard is usually the answer
- You have a hipped roof rather than a gable end. A Hip-to-Gable conversion squares off the slope first, then the dormer goes on top
- You just want a bit more light, not extra floor space. A Velux conversion is cheaper and faster
Still unsure? Daniel will tell you straight at the free survey. book one here →
How does a dormer compare to other loft conversions?
| Type | Build time | Floor area added | Planning | Best for |
|---|---|---|---|---|
| Velux | 6–8 weeks | Smallest | Usually permitted development | Homes with enough existing headroom and a leaner budget |
| Dormer | 8–10 weeks | Large | Usually permitted development | Victorian and Edwardian terraces, 1930s semis |
| L-Shaped Dormer | 10–12 weeks | Largest (two rooms) | Often permitted development | Victorian terraces with a rear back addition |
| Hip-to-Gable | 10–12 weeks | Large | Usually permitted development | Semi-detached and end-of-terrace with hipped roofs |
| Mansard | 12–16 weeks | Largest single room | Planning permission required | Conservation areas, period properties needing maximum space |
Your dormer loft conversion, week by week
From your first call through to the day you move back in: a clear, predictable timeline that protects your home and your schedule.
- Week 0
Step 01
Free home survey
Daniel measures the roof, checks the ridge height and existing services, and tells you on the visit whether a dormer is feasible. If it isn't, he'll recommend the type that is.
- Weeks 1–3
Step 02
Fixed-price proposal
Design drawings, structural approach and a fully itemised fixed-price proposal, with every cost on its own line. A 15% deposit secures your build slot.
- Weeks 4–8
Step 03
Drawings, planning and party wall
We confirm permitted development with a Lawful Development Certificate, finalise structural calculations, submit Building Control and serve party wall notices. You deal with none of it.
- Weeks 9–20
Step 04
Build on site
Scaffold up day one, the roof opened and weatherproofed in week 2, structure complete by week 6 and finishes wrapped by week 10. Weekly photo updates by WhatsApp.
- Week 21+
Step 05
Handover and 5% retention release
Final walk-around, completion certificate and written guarantees. 5% of the contract is held in retention until you've signed off the snagging.
Dormer loft conversion questions, answered
How much does a dormer loft conversion cost in London?
A dormer loft conversion in London typically costs £52,000 to £68,000, VAT included.
The lower end gets you a single double bedroom with standard finishes. The mid-range adds an en-suite shower room. The upper end gets you a premium en-suite, engineered wood floors and fitted joinery.
Every quote is itemised line by line, with no provisional sums.
Do I need planning permission for a rear dormer?
Usually not. Rear dormers on houses normally fall under permitted development, so we apply for a Lawful Development Certificate instead, which typically takes 6 to 8 weeks.
You will need full planning permission if your property is a flat or maisonette, if the dormer faces the street, or if your rear elevation sits in a conservation area.
We confirm which route applies at the free survey and handle the whole application either way.
How long does a dormer take to build?
Around 8 to 10 weeks on site: the roof opens in week 2 with temporary weatherproofing installed the same day, steels and the new floor go in by week 3 to 4, the dormer structure completes by week 5 to 6, and finishes wrap in weeks 8 to 10.
Add the design, certificate and party wall stage beforehand and the full journey from first call to handover is roughly 16 to 22 weeks.
How much floor space does a dormer add?
Typically 18 to 26 square metres of usable floor area, depending on the width of your roof and the size of the dormer. That is comfortably enough for a double bedroom with full standing headroom, and on most terraces an en-suite shower room as well.
Will a dormer look out of place at the back of my house?
Done properly, no. The dormer is clad in slates, tiles or cladding chosen to match your existing roof, and it sits on the rear elevation where it isn't visible from the street.
On most South London terraced streets, several neighbours will already have one, which is usually a good sign for both planning and how it will look.
Will a dormer make my house too hot in summer?
Not if it is insulated correctly. Building Regulations require high-performance insulation in the dormer walls and flat roof, which keeps heat out in summer as well as in during winter.
We also position openable windows for cross-ventilation, and blinds or glazing upgrades can be specified for south-facing rooms.
Other loft conversion types we build
L-Shaped Dormer
Two dormers joined in an L over the rear and side return. Adds two rooms, typically a bedroom and a generous bathroom.
About L-Shaped Dormer conversionsMansard
A full new storey behind a steep rear wall. The highest spec, the biggest space, often required in conservation areas.
About Mansard conversionsHip-to-Gable
Squares off a sloping side roof to create the volume needed for a proper room, perfect for semi-detached and end-of-terrace homes.
About Hip-to-Gable conversionsVelux / Rooflight
The simplest, fastest, lowest-cost option. It works inside the existing roof with skylight windows, often without planning permission.
About Velux / Rooflight conversionsDormer loft conversions across London
Dormers are the most common conversion we build, and they're particularly suited to the Victorian and Edwardian terraced stock that dominates Clapham, Wandsworth, Balham and Tooting in South London, and Chiswick, Ealing and Fulham in the West.
Tap any area to see what's possible on a house like yours.
Ready to see what a dormer could do for your home?
Tell us your postcode and a bit about your house.
Daniel will arrange a free home survey to confirm whether a dormer is the right call, and if it is, you'll have a fully itemised fixed-price proposal within 7 days of the visit.
If it's not, he'll tell you that too and recommend the right type for your house.
- Free home survey, usually within 5 working days
- Itemised fixed-price proposal within 7 days of the survey
- 15% deposit only after you sign · 5% retention held until snagging is signed off
- VAT included in every figure
Prefer to talk? Call Daniel on 07414 648 263.