Loft conversion architects

A loft is usually the cheapest square metre you will ever add to a London house. It is also the one most often refused, because the roof form, the dormer size and the borough's Article 4 rules all have to line up.

We survey the roof, work out the head height you actually have, and design the largest conversion the rules will allow — then take it through the route that gets you built fastest.

Types of loft conversion we design

Rear dormer

The workhorse of the London loft. A flat-roof box dormer across the rear slope gives you full head height, a double bedroom and an en-suite. Usually possible under permitted development on a house, subject to volume limits.

Hip-to-gable

For semi-detached and end-of-terrace houses with a hipped roof. The sloping side is built up into a vertical gable wall, then combined with a rear dormer. Adds far more usable floor area than a dormer alone.

L-shaped dormer

Where a Victorian or Edwardian house has a rear outrigger, the dormer wraps around into it. Two bedrooms and a bathroom are often achievable.

Mansard

The roof is rebuilt with a near-vertical rear slope at around 70 degrees. It gives the most space and often the best result in conservation areas, but it almost always needs full planning permission.

Rooflight (Velux) conversion

No change to the roof shape, just insulation, a staircase, structural work and rooflights. Cheapest and quickest, and normally permitted development — but only works where you already have the head height.

Permitted development or planning permission?

Many loft conversions on houses fall under permitted development, which means no planning application is needed. The main limits are:

• Additional roof volume of up to 40 cubic metres for terraced houses, or 50 cubic metres for detached and semi-detached houses.
• Nothing forward of the front roof plane facing a highway.
• No part higher than the existing ridge.
• Materials similar in appearance to the existing house.
• Side-facing windows obscure-glazed and non-opening below 1.7m.

Where permitted development applies, we recommend a Lawful Development Certificate. It is a formal confirmation from the council that the work is lawful — worth having when you sell, and often asked for by lenders and buyers' solicitors.

Head height and structure

As a rough guide you want around 2.2 to 2.4 metres from the top of the existing ceiling joists to the underside of the ridge before conversion. Less than that and a dormer or mansard may still work, or the ceiling below can be dropped. We measure this on the survey rather than guessing from photos.

The existing ceiling joists are almost never strong enough for a floor. New steel beams normally span between the party walls to carry new floor joists. We coordinate with a structural engineer and produce the drawings your building control body needs.

Regulations that shape the design

• Part K — stairs. A fixed staircase is required, with 2m headroom (1.9m at the centre and 1.8m at the edge is accepted for loft stairs).
• Part B — fire. On a three-storey house you need a protected stair enclosure, fire doors to habitable rooms off the stair, and mains-powered interlinked smoke alarms. An escape window alone is not enough.
• Part L — insulation. Warm-roof or cold-roof build-ups to meet current thermal standards.
• Party Wall etc. Act 1996. Cutting steels into a shared party wall requires notice to your neighbours, usually two months before work starts.

Typical programme