Feasibility before drawings
We measure head height, identify the roof structure and check the stair landing before you commit to design fees, so you find out what is possible while it is still free to change your mind.
Property Enhancements / Loft Conversions
Loft Conversions in London
Dormer, Velux and storage conversions that add space without losing any garden, managed from structural work to final finish.
Get a loft surveyThe extra bedroom is already in your roof
This page is for owners of terraced and semi-detached houses in South and West London thinking about converting the loft into a bedroom, office or bathroom. K & M Roofing Solutions handles the whole conversion, from checking whether your roof can take one through to a finished, decorated room.
On a standard London terrace the answer is usually yes, but it depends on the roof. A traditional cut roof with purlins and rafters converts easily. A trussed roof, common on post-war infill, needs the trusses removing and steels putting in, which changes the cost. The number that decides it is head height: you need roughly 2.2 metres from the existing ceiling joists to the ridge before a conversion works without a dormer.
That is why we survey before anyone spends money on drawings. A feasibility visit measures the head height, identifies the roof type, checks where the stairs can land and tells you which conversion your house actually supports. Plenty of people pay an architect first and find out the constraints afterwards.
Benefits
How we approach a loft conversion
Roof and structure, one contractor
The steels, the dormer and the roof covering are all ours, so the part of a loft conversion most likely to leak is not handed to whichever roofer was available that week.
Planning and regulations handled
We deal with Permitted Development, the planning application where one is needed, the Building Regulations notification and the inspections, including conservation area and Article 4 constraints.
Finished, not shelled
The price covers plastering, stairs, electrics, plumbing, insulation and decoration, so what you get back is a room you can move into, not a shell needing another contractor.
What we offer
Types of loft conversion we build
Rear dormer
A flat-roofed box built out from the rear slope, which is the standard London terrace conversion because it turns unusable sloped space into full head height across most of the floor. Usually Permitted Development at the rear, and the roof over it is a flat roof we waterproof ourselves.
See how we waterproof a flat roofVelux conversion
Windows fitted into the existing slope with no change to the roof shape, which is the cheapest and quickest option and almost never needs planning permission. It only works where you already have the head height, so the survey decides it.
Mansard conversion
The rear slope rebuilt at a steep angle to create close to a full extra storey. It gives the most space of any conversion, needs planning permission in most cases, and is common on the taller Victorian terraces across South and West London.
Hip to gable
The sloping hip end squared off into a vertical gable wall, which is how you make a semi-detached or end-terrace loft usable. Frequently combined with a rear dormer on the same job.
Structural work and steels
Trusses removed, steel beams installed and floor joists strengthened to take a habitable load. This is what separates a real conversion from boarding out a loft, and it is engineer-designed and building control inspected.
Full fit-out
Stairs, insulation to current regulations, fire doors and protected escape route, electrics, plumbing for an en suite, plastering and decoration, finished ready to use.
How it works
How our loft conversion service works
1
Feasibility survey
We measure the head height, identify the roof structure, check where the stairs can land and confirm which conversion types your house supports. Free, and about an hour.
2
Design and structural drawings
Architectural drawings and structural engineer calculations for the steels, produced once you know what is feasible rather than before. Typically two to four weeks.
3
Planning and building control
We confirm whether it is Permitted Development or needs a planning application, submit it, and lodge the Building Regulations notification. Planning takes about eight weeks where an application is required.
4
Structural phase
Scaffold up, roof opened, trusses removed where needed, steels craned in and the new floor structure built. The roof is made watertight at the end of each working day.
5
Shell and services
Dormer built and waterproofed, windows in, insulation, stairs formed, electrics and plumbing first fixed. This is the longest phase and typically runs four to six weeks.
6
Fit-out and sign-off
Plastering, second fix, decoration, then building control final inspection and completion certificate, handed over with the 10-year workmanship guarantee.
Why choose us
Why customers choose K & M Roofing
01
Certified HYDRONYLON applicators, a system most London roofers cannot offer.
02
One team for the whole job, from survey to sign-off.
03
Rated 5.0 by 60 customers on Google.
04
Fully insured with public liability cover, with certificates issued to you and to building control before we start on site.
05
Transparent pricing with no hidden costs, and a 10-year workmanship guarantee.
Common questions
Frequently asked questions
As an indicative market range for 2026, London loft conversions typically run £50,000 to £90,000 excluding VAT, and that is a range rather than a quote. What moves it is the type: a Velux conversion sits at the bottom because the roof shape does not change, a rear dormer sits in the middle, and a mansard or a hip-to-gable with a dormer sits at the top because you are rebuilding a large part of the roof. Trussed roofs cost more than traditional cut roofs because the trusses have to come out and steels go in, and an en suite adds plumbing and drainage. A binding price from K & M Roofing Solutions follows a free survey.
Often not. Rear dormers on a terraced or semi-detached house usually fall under Permitted Development, within volume limits of 40 cubic metres for a terrace and 50 for a semi or detached house. You will need a full planning application for a mansard, for anything on the front elevation facing a highway, and for any conversion in a conservation area or where an Article 4 direction applies, which covers a good deal of South and West London. Building Regulations approval is required either way and is a separate process.
A dormer is a structural box built out from the roof slope that creates full head height across the floor area, while a Velux conversion fits windows into the existing slope and leaves the roof shape untouched. The dormer gives considerably more usable space and is the standard London terrace answer; the Velux is cheaper, quicker and rarely needs planning permission, but only works if you already have the head height. The survey tells you whether Velux is even an option for your roof.
Ten to sixteen weeks on site for a typical rear dormer, plus the design and approvals beforehand. Allow two to four weeks for drawings and structural calculations, and about eight weeks for planning where an application is needed, so the whole process from first survey to finished room is commonly four to six months. A Velux conversion is faster because the roof structure barely changes.
The two things that decide it are head height and roof type. You need roughly 2.2 metres from the top of the existing ceiling joists to the underside of the ridge; below about 2 metres a conversion needs either a dormer or lowering the ceiling below. A traditional cut roof with rafters and purlins converts straightforwardly, while a trussed roof needs the trusses removed and steels installed, which is entirely doable but costs more. We measure both on the feasibility visit before you spend anything on design.
Usually not. Most of the structural work happens through the roof from scaffold outside, so the house stays liveable for the majority of the programme. The disruptive periods are the day the ceiling opens up and the week the staircase goes in, because that affects the floor below. Dust protection and a sealed route are set up at the start, and we agree working hours before we begin.
The conversion carries a 10-year workmanship guarantee issued in writing at handover, alongside the Building Regulations completion certificate, which is the document a future buyer or lender will ask for. The dormer roof is covered by the same guarantee, and where it is finished with HYDRONYLON it also carries the separate 10-year product guarantee from HYDRONYLON LTD. Structural calculations are certified by the engineer independently.
Free on-site estimate
Let us talk about your roof
Tell us what is going on and we will arrange a free survey. No pressure, no hard sell, just honest advice and a clear price.
Kamil07593 196505
Mateusz07544 188268