The roof plan is the view nobody on the street ever gets, and the one drawing that shows how water leaves your building. Leave it out and the council does not refuse you — it returns the application as invalid, which means the eight-week clock never started.
Every pitch and its direction, ridges, hips and valleys, chimneys, rooflights, and for a flat roof the falls and every rainwater outlet. It is drawn looking straight down at 1:50 or 1:100. Existing and proposed versions are both required wherever a scheme alters the roof, which most London loft schemes do.
| Permitted development, roof enlargement | Allowance |
|---|---|
| Terraced house, added volume | 40 m³ |
| Semi-detached or detached, added volume | 50 m³ |
| Set back from the original eaves | 200 mm (hip-to-gable exempt) |
| Height above the existing highest roof | Not permitted |
| On the principal elevation fronting a highway | Not permitted |
| Anywhere on designated land, including conservation areas | Not permitted |
Source: Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, Class B, as amended. Allowances are cumulative and include any previous enlargement of the roof, including one carried out by a previous owner.
A roof plan is the view nobody standing on the street ever gets: the building seen from directly above. It is the drawing that resolves how the roof is actually shaped and, on anything with a flat element, how water gets off it.
Councils ask for one whenever the roof changes, and in London that is most householder work. A rear dormer changes it. A hip-to-gable changes it. A mansard replaces it. Even a single-storey rear extension changes it, because the new roof has to meet the existing one somewhere and the roof plan is where that junction is described. You need an existing and a proposed version, because the officer is assessing the difference between them, not the proposal in isolation.
Where the roof plan is missing from a submission, the application is usually returned as invalid rather than refused — which sounds better than it is. An invalid application has not started, so the eight-week clock has not started either.
| Element | Why it is on the drawing |
|---|---|
| Pitch direction and angle | Establishes the roof form and lets the officer check it against the street |
| Ridges, hips and valleys | Defines the geometry; a valley is where two roofs meet and where leaks start |
| Chimneys and flues | Retained stacks affect both appearance and the position of any dormer |
| Rooflights and dormers | Position, size and whether they sit on the front or rear slope |
| Falls on flat areas | Minimum 1:80 as designed, so the built fall still drains after deflection |
| Rainwater outlets and gutters | Shows where water goes; a flat roof with no outlet shown is not a designed roof |
| Parapets and upstands | Minimum 150 mm upstand at abutments under Part C |
| North point and scale bar | Orientation matters for overshadowing and for solar gain under Part L |
The one most often left off a homeowner-drawn roof plan is the rainwater outlet. It is easy to see why: it is small, and on a pitched roof the gutter is obvious. On a flat roof it is neither, and a flat roof drawn without outlets has not been designed, only shaped.
If you are hoping to build under permitted development rather than apply for planning permission, the roof plan is the drawing that proves you can. Class B of Schedule 2, Part 1 of the General Permitted Development Order allows an enlargement of the roof within a volume allowance, and volume is calculated from the roof geometry — which only the roof plan and the sections together describe.
Three things catch people out. The allowance is cumulative, so a previous owner's dormer counts against your 40 or 50 cubic metres. The 200 mm set-back from the original eaves applies to a dormer but not to a hip-to-gable. And none of Class B is available on designated land, which includes every conservation area — a significant constraint in inner London, where Camden alone has 40 conservation areas on the national register.
Article 4 directions are a separate question, and worth not conflating with this one. They can remove permitted development rights, but they do not all remove the same ones: across London the great majority withdraw the commercial-to-residential right rather than anything a householder uses, and only five boroughs — Barnet, Brent, Waltham Forest, Hillingdon and Westminster — withdraw the householder extension right at all. Camden has 21 Article 4 areas on the register, and for not one of them does the register say which rights it withdraws — so the only safe step is to read the direction covering your address rather than assume it reaches your roof.
Where permitted development is not available, the route is a full application, and our planning application drawings cover it. Where it is available but contested, the right document is a Lawful Development Certificate rather than a planning application — a different form, a statutory fee of £274 rather than £548, and a legal test rather than a planning judgement.
Source: MHCLG District Planning Application Statistics (PS1 and PS2), decisions made in the twelve quarters 2023 Q2 to 2026 Q1, retrieved 1 September 2026. Open Government Licence v3.0.
A flat roof is a pitched roof that has given up most of its angle. It still needs one. The convention is to design to a 1:80 fall so that the built result still achieves 1:120 after the deck deflects — design for the fall you want to end with, not the one you want to draw.
The roof plan sets three things a builder cannot invent: which way the fall runs, where the outlets sit, and where the upstands are. Get the fall running towards a parapet with no outlet and you have built a swimming pool. It happens, and it happens because the roof plan said 'flat roof' and nothing else.
We do not sell drawings individually. A roof plan is part of every package, because a set that is missing one drawing is a set that comes back.
| Package | Fixed fee | Turnaround |
|---|---|---|
| Essentials — survey, existing and proposed plans | from £840 | 14–20 working days |
| Loft conversion package | from £1,225 | 14–20 working days |
| Mansard / roof rebuild package | from £1,575 | 18–24 working days |
| Complete — planning plus building regulations | from £1,750 | 20–28 working days |
A volume. The permitted development right for roof additions is not expressed as a depth or a height — it is a cubic content limit, 40 cubic metres for a terraced house and 50 for anything else, and it counts every previous roof enlargement, not just yours. That is unusual among the householder rights, and it is why roof drawings get returned more often than wall extensions do. A depth you can read off a plan. A volume has to be derived, and it can only be derived if the drawings give someone the three dimensions to derive it from.
In practice that means the roof plan cannot travel alone. It needs sections through the enlargement at the points where its profile changes, existing and proposed on the same sheet or at the same scale, so the added solid is recoverable. If an officer cannot compute the figure, the safe answer for them is to refuse or to ask — and asking costs you weeks.
Four further conditions are checkable straight off the drawings, and each is a common failure:
| Condition | What must be visible on the drawing |
|---|---|
| No higher than the existing roof | Both ridge heights dimensioned from the same datum |
| Not beyond the principal elevation roof slope facing a highway | Which slope fronts the highway, marked on the plan |
| Eaves set back at least 0.2m from the original eaves | The set-back, measured along the roof slope, not horizontally |
| Materials of similar appearance | A materials note against the new roof surfaces |
One consequence catches people out on terraces. Because the limit counts every previous roof enlargement and not merely the one you are proposing, a house that already carries a rear dormer from the 1980s may have little or none of its 40 cubic metres left. The volume was spent by someone you have never met, and no survey of your own roof will tell you so — only the drawings of what the roof originally was.
Source: Town and Country Planning (General Permitted Development) (England) Order 2015 (SI 2015/596), Schedule 2, Part 1, Class B, paragraphs B.1 and B.2. Retrieved 3 September 2026. Open Government Licence v3.0. Class B is not available on article 2(3) land, which includes conservation areas.
A drawing of the roof seen from directly above, normally at 1:50 or 1:100. It shows every pitch and its direction, the ridges, hips and valleys, chimneys, rooflights, flat-roof falls and the position of every rainwater outlet and gutter. It is the only drawing that shows how water actually leaves the building.
For anything that alters the roof, yes, and most London councils list it among the required drawings on their validation checklist. A dormer, a mansard, a hip-to-gable or a rear extension with a new roof all change the roof plan, so existing and proposed versions are both needed.
Nothing. They are two names for the same drawing. Some councils and some suppliers use 'roof layout', others 'roof plan'. If a validation checklist asks for one and your set contains the other, it is the same document.
Especially a flat roof. A flat roof is never actually flat — it needs a minimum fall, normally 1:80 as designed to allow for deflection, and the roof plan is where those falls and the outlet positions are set. Without it the fall gets decided on site and water ponds.
40 cubic metres on a terraced house and 50 cubic metres on a semi-detached or detached house, measured as added volume and including any previous roof enlargement. None of it is permitted development on designated land, which includes conservation areas — and much of inner London is designated.
It is included in every package we produce, from £840 for Essentials. We do not price drawings individually, because a set missing one drawing is a set that gets returned.
Site plans are included in every drawing package we produce, on a licensed Ordnance Survey base with the ownership edging done properly.
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Each area page carries the local planning authority, conservation-area position, postcode districts and typical housing stock for that address.
