Extensions & Projects · Essex & East London
The loft is the only extra room in the house you have already paid for. It sits inside the existing walls and takes nothing from the garden. Depending on the type you are either finishing a space that is already there or rebuilding part of the roof over it, but either way the footprint is free, which is why it is the best value floor area you can add.
Why the loft
Every other way of adding space costs you ground. A loft conversion is the one move that adds a bedroom without touching the garden, the drive or the boundary.
No foundations, no excavation, no new external walls to speak of. You are paying to finish a space rather than to create one.
The only way of adding a bedroom that takes nothing from outside. On a small plot it is often the only option left.
Most rear dormers and hip-to-gable conversions fall inside permitted development. We confirm yours in writing before design starts.
A loft usually gives a principal bedroom with an ensuite off it. That pairing is what moves a house up a bracket, more than the floor area does.
Types
These are not styles, they are different amounts of building work. The first takes nothing off the roof. The last rebuilds half of it. Which one your house can have is decided mostly by its roof shape and how much height is under the ridge.
Nothing changes outside except the windows. The roof stays exactly as it is and the rooflights sit flush in the slope. The quickest and cheapest conversion by a distance, but it only works if the head height is already there.
A flat-roofed box built out from the rear slope, turning a triangular loft into a room with a flat ceiling and a full-height wall. The most common loft conversion in Essex, and usually the best value for the space it creates.
Two dormers built as one: across the rear of the main roof, then turning the corner and running down the flank of the outrigger. More space than any other dormer, and often a second room rather than one.
The sloping hipped end is rebuilt as a vertical gable wall, so the loft gains full-height space right out to the end of the house. Almost always paired with a rear dormer, which is what makes it a room.
The rear roof is rebuilt at about 70 degrees with a flat deck on top. It gives the most floor area of anything you can do to a terrace, and involves more building work than anything else, which is why it costs what it does.
| Extension type | Build cost | Time on site | Planning | Best suited to |
|---|---|---|---|---|
| Rooflight | £1,150–£1,600 /m² | 5–7 weeks on site | Permitted development | Roofs that already have the height, and conservation areas |
| Dormer | £1,600–£2,200 /m² | 8–12 weeks on site | Usually permitted development | Semis and terraces with a rear roof slope |
| L-shaped dormer | £1,750–£2,350 /m² | 12–16 weeks on site | Usually planning permission | Victorian and Edwardian houses with a rear outrigger |
| Hip to gable | £1,850–£2,450 /m² | 10–14 weeks on site | PD if the pair stays under 50 m³ | 1930s semis and detached houses with a hipped end |
| Mansard | £2,100–£2,800 /m² | 12–16 weeks on site | Planning permission required | Terraces and town houses where a dormer isn't enough |
Our work
Every project starts as a drawing. These are ours: the plans, sections and approvals behind the finished rooms.
Costs
Loft costs track the type far more closely than the size. A mansard costs roughly twice what a rooflight conversion does for about a third more floor area, because one leaves the roof alone and the other rebuilds it.
Typical rear dormer
£1,600–£2,200 /m²
Per m² of new floor area created in the loft. Build cost only.
| Conversion type | Floor area created | Indicative build cost |
|---|---|---|
| Rooflight | 20–28 m² | £23,000 – £44,000 |
| Dormer | 25–33 m² | £40,000 – £72,000 |
| L-shaped dormer | 33–42 m² | £58,000 – £98,000 |
| Hip to gable with rear dormer | 30–38 m² | £55,000 – £92,000 |
| Mansard | 30–40 m² | £63,000 – £110,000 |
This is the comparison most people are actually making:
| Built as | Rate per m² | Garden lost |
|---|---|---|
| Rear dormer loft | £1,600 – £2,200 | None |
| Single-storey rear extension | £2,400 – £3,200 | The full footprint |
Roughly 30% less per m², and it costs you nothing outside. The trade is that a loft gives bedrooms, not living space, so for most people the two are answering different questions.
Build cost only.
Ask three builders and you'll get three numbers. What matters is they're pricing the same specification. That is exactly what a proper technical package gives you.
Costs reviewed September 2026 · next review March 2027
What kind of home is it?
Detached
Semi-detached
Terraced
Bungalow
Our design fee
One figure covering survey, concept design, the planning application or lawful development certificate, and the Building Regulations package, quoted after our first conversation.
Use the design cost calculatorEverything else follows from this. Measure from the top of the ceiling joists to the underside of the ridge. The new floor and the insulation take roughly 250–300 mm of it, so at 2.4 m you have a conversion with nothing to design around. Between 2.2 m and 2.4 m it is still doable, but the layout has to work harder.
Below about 2.2 m the options are raising the ridge or lowering the ceilings underneath, and both change the cost enough that they need deciding at initial consultation and feasibility rather than halfway through a design.
Planning
Loft conversions have their own permitted development class, and it is measured in volume rather than in metres. Two numbers do most of the work.
The volume allowance. A roof enlargement can add up to 40 m³ on a terraced house and 50 m³ on a semi or detached house, and that counts every roof enlargement the house has ever had, including a previous owner's. A rear dormer typically uses most of a terrace's allowance on its own, which is why an L-shaped dormer usually goes over.
Usually an application, and rarely a refusal. Nothing may extend beyond the roof slope of the principal elevation where that elevation fronts a highway, so on a normal road-facing house a front dormer needs a householder application however modest it is. On a backland plot or a house facing a green rather than a road, the rule does not bite and the volume allowance is what governs. That is a procedural point, not a design objection: where a street already has front dormers, councils grant them regularly. Where it has none, we would usually put rooflights to the front, which are permitted development provided they project no more than 150 mm beyond the roof plane and sit below the highest part of the roof, and keep the dormer at the rear.
Building Regulations
The moment a two-storey house becomes a three-storey one, a set of requirements switches on that had nothing to do with the house before. This is where loft conversions are genuinely different from other work.
A new floor spanning wall to wall, sitting on the masonry rather than on the ceiling joists below. Steels where the span is long, the trusses are coming out or a chimney breast is being removed.
The stair becomes a protected escape route to the front door. Fire doors to every room off it, mains-linked alarms throughout, and usually alterations downstairs that people don't expect.
Two different standards. The existing roof slopes you keep are upgraded to 0.16 W/m²K at rafter level. Anything new, whether a dormer roof, its cheeks or a mansard slope, is a new element at 0.15 for roofs and 0.18 for walls. The build-up takes head height, which is why it gets designed early rather than specified at the end.
2 m of headroom over the flight, relaxed to 1.9 m at the centre and 1.8 m at the edge where a sloping ceiling crosses it. That relaxation is what makes a great many conversions possible at all.
The stages
Click into any stage for what happens, what you receive, and what comes next.
Honest, early advice on what's realistic for your property, budget and how you want to live.
Options on the table exploring layout, light and flow, so you can react to real ideas.
We prepare and submit the right application, designed to give your scheme its best chance.
The approved concept is developed into a coordinated, buildable set of drawings.
Lofts we've designed
Bedrooms, suites and dressing rooms carved out of roof space, bright, calm and properly finished.
FAQs
It depends far more on the type than the size. A rooflight conversion runs £23,000–£44,000, a rear dormer £40,000–£72,000, and a mansard £63,000–£110,000. As a rate, a typical rear dormer works out at roughly £1,600–£2,200 per m² of new floor area. Indicative build cost only, excluding fitted furniture, an ensuite, fees and VAT.
Per square metre, yes, and by a real margin. A rear dormer runs about £1,600–£2,200 per m² against roughly £2,400–£3,200 for a single-storey rear extension, because there are no foundations, no excavation and the walls and roof already exist. It also takes nothing from the garden, which is often the deciding factor.
Usually not, if the work is to the rear or the side slope. Permitted development allows an added volume of 40 m³ on a terrace and 50 m³ on a semi or detached house, counting anything a previous owner already added. Mansards and L-shaped dormers regularly go past that. On designated land no roof enlargement is permitted development at all, though rooflights still are.
Not under permitted development, whatever its size. Nothing may extend beyond the roof slope of the principal elevation where that elevation fronts a highway, which on a normal road-facing house means a front dormer always needs a householder planning application. That is not the same as it being refused. Where a street already has front dormers, they are granted regularly. Where the street has none, we would normally put rooflights to the front and keep the dormer at the rear. Front rooflights are permitted development, because they sit in the plane of the roof. They may project no more than 150 mm beyond it and cannot sit above the highest part of the roof.
About 2.4 m from the top of the ceiling joists to the underside of the ridge and the conversion is straightforward, with no complications to design around. It is not a Building Regulation. There is no legal minimum ceiling height for a loft room in England at all. What the regulations do fix is the stair: 2 m of headroom over the flight, relaxed to 1.9 m at the centre and 1.8 m at the edge where a sloping ceiling crosses it. Between roughly 2.2 m and 2.4 m it can still be done but the design has to work at it. Below 2.2 m you are into raising the ridge or dropping the ceilings underneath, and both change the economics.
Most houses built from the 1970s on have trussed rafter roofs, and the W-shaped webs run straight through the middle of the space. They can be cut out, but only once a new structural floor and new support to the roof are in, which is a structural engineer's job and adds cost. It does not stop the conversion; it changes the price and the sequence.
This is the question that decides more loft schemes than cost does. The new flight has to land somewhere with headroom over it, which usually means over the existing stair, and that often takes a slice out of the small bedroom. Turning a three-bedroom house into a four-bedroom one is worth doing; turning it into a house with three usable bedrooms and a box room is not. We work the stair out before anything else.
Only if it was signed off. A loft room without a Building Control completion certificate causes trouble at sale: the buyer's solicitor asks for it, the surveyor recommends a specialist report, and the lender can make it a condition. The certificate is what turns a loft room into a bedroom on paper.
Nationwide's research puts a loft double bedroom plus a bathroom at up to 24%, but that figure is specifically a three-bedroom, one-bathroom house becoming a four-bed with two. A bedroom on its own is nearer 10%, and going from two bedrooms to three around 13%. Those are national averages, and every street has a ceiling above which buyers stop paying whatever you have built. Local evidence beats national research every time.
On a terrace or a semi, almost certainly. Cutting into the party wall for a beam, bearing new floor joists on it, or building a new gable up off a wall sitting on the boundary all bring the Party Wall etc. Act 1996 into play, and notice has to be served before work starts. Note that on a semi the hipped end is usually your own flank wall, not the party wall. It is the beams going the other way that catch you.
Allow 8–14 weeks from first consultation to a decision or a lawful development certificate, then 5–7 weeks on site for a rooflight conversion, 8–12 weeks for a rear dormer and 12–16 weeks for a mansard or an L-shaped dormer.