L-shaped dormer drawings in City of London

How the City guides alterations to residential roofs

The adopted plan is the City of London Local Plan 2015, and the one residential guidance document the council lists is the Barbican Estate Listed Building Management Guidelines: Volume I Introduction and Volume II Residential (SPD). It covers the Barbican, where roofs and terraces are tightly controlled, and it shows the council expects alterations to respect an original design.

We read the plan and the guidance together with your building rather than copying a generic dormer. If your property sits outside the Barbican, the same principle applies: officers want to see that the new roof volume follows the architecture beneath it.

Why the figures are thin and what that means for you

The council decided just 1 householder application in its latest year, out of 477 decisions of every type. With a single case, the granted rate of 100 per cent says nothing useful about your chances, so we do not lean on it.

The wider picture is steadier: 97.1 per cent of minor applications were granted, and 93.1 per cent were decided in time. Those are commercial and conversion schemes, but they show an authority that processes work promptly when the drawings are clear.

Permitted development rarely applies here

Nationally, an L-shaped dormer relies on one useful allowance: Eaves-retention and 0.2 m set-back do not apply where the enlargement joins the original roof to the roof of a rear or side extension. Volume is capped at 40 m³ (terrace house) / 50 m³ (any other house) additional roof volume, and No part higher than the highest part of the existing roof.

None of that helps inside a conservation area, because Class B roof enlargements are not permitted development on article 2(3) land. With 28 conservation areas in so small a place, most City addresses fall under that rule, so a planning application is the normal route and a certificate is the exception.

If you want the national rules in full, the L-shaped dormer drawings guide sets them out for every London borough.

Party walls, stairs and fire in a dense building

Buildings here share structure on several sides. Cutting into a shared roof needs notice: Party structure notice at least 2 months before work. We prepare the notice drawings alongside the planning set.

The stair must still meet the headroom rule, 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). Taller buildings bring the fire rule into play as well: 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). In a tight plan both can decide where the dormer door goes before the roof shape is settled.

Starting a City enquiry

Send us the address and, if you have it, the listing entry or the lease. Many City homes are held on long leases with the freeholder's consent needed for roof works, and that consent runs on its own timetable. We ask early so the programme has no surprise in it.

What we deliver and who to ask next

You receive existing and proposed plans, a roof plan, sections through the junction and four elevations, checked by a second MCIAT chartered technologist. If the council asks for changes, we redraw at no charge until approval.

If an L-shape is too large for the building, a dormer loft conversion in City of London may fit instead. For the wider picture of the area, see our architectural drawings in City of London page, and for a similar borough with more terraces look at L-shaped dormer drawings in Westminster.