Dormer loft conversion drawings in London

Volume, position and height limits

Under permitted development the first constraint is volume: 40 m³ (terrace house) / 50 m³ (any other house) additional roof volume. Everything added to the roof counts, including earlier work.

Position is the second. No enlargement beyond the plane of a roof slope that forms the principal elevation and fronts a highway. So the dormer sits on the rear or a side slope that does not face the road.

The third is the set-back from the edge: Original eaves maintained; enlargement set at least 0.2 m from the eaves measured up the roof slope, so far as practicable (not required for hip-to-gable or roofs joining a rear/side extension). This is why a dormer has a strip of original roof below its cheek, rather than coming flush with the wall.

Careful planning of these three limits usually gives you a design that stays inside the permitted route, which saves an application and its fee.

Materials and side windows

The visible finish has to fit the house. The rule is: Exterior materials similar in appearance to the existing house. Tile hanging, zinc and cladding are all used on London dormers, and choosing something close to the existing roof keeps the route simple.

Windows on the side of a dormer have their own condition: Upper-floor side windows obscure-glazed and non-opening below 1.7 m above floor. On a semi-detached house, that matters because the side cheek of the dormer faces the neighbour.

A planning application gives more freedom on materials, at the cost of the fee and the decision period. We advise you which route fits your design before drawing it.

Conservation areas and the planning route

A dormer is a roof enlargement, and the rule is firm: Class B roof enlargements are not permitted development on article 2(3) land. A rear dormer in a conservation area therefore needs planning permission, and the design is judged on its effect on the area.

A conservation area does not rule one out. Officers tend to prefer a dormer that is set well below the ridge, in from the sides and clad to match, and they dislike one that dominates the roof. We draw to those expectations from the start.

The application runs through planning drawings. If your design is within the permitted limits, a Lawful Development Certificate proves it in writing, which is useful when you sell.

Stairs, fire safety and the new roof

The stair has to be sized properly. The reduced standard for lofts is: Loft conversions where 2.0 m cannot be achieved: 1.9 m at the centre of the stair, 1.8 m at the side (half width).

The fire rule for a new storey is: New storey above 4.5 m by loft conversion: protect the full escape route with fire-resisting doors (min E 20) and partitions (min REI 30). That means fire-resisting doors on the escape route, which we show in the plan and the specification.

The new flat or pitched roof over the dormer has an energy target: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. A flat roof with deep insulation can add height to the dormer, so the build-up goes onto the section before the dormer height is fixed.

Steel at the dormer opening is sized by the engineer, and we coordinate it through structural calculations.

Cost and what you receive

Dormer loft conversion drawings start at £695, VAT included, fixed and published before you commit.

The set has existing and proposed plans, elevations and sections, with the dormer, stair and roof build-up shown, along with location and block plans. The building control package follows through our building regulations drawings.

A second MCIAT chartered technologist checks every sheet. If the council asks for changes, we redraw at no charge until approval.

Dormer drawings by council

Boroughs have their own roof extension guidance, and what is acceptable in one street can be refused in the next. Your council's figures are on the pages under architectural drawings by area.

Have a rear outrigger? An L-shaped dormer is built for that. Prefer less change to the roof? See Velux loft conversion drawings, or compare all types under loft conversion drawings.