Roof terraces and the overlooking objection

A roof terrace on a flat always needs planning permission. The permitted development rights in Part 1 of Schedule 2 to the General Permitted Development Order apply to dwellinghouses, and a flat is not a dwellinghouse for those purposes, so there is no equivalent of the householder route. Roof terrace planning overlooking is therefore the whole of the argument, because the application is going in regardless and what decides it is the effect on neighbours rather than whether a right exists.

For a landlord or an investor converting a building, that changes the economics. The terrace is a value item that carries application risk and, if granted, a set of conditions you will have to live with.

What the application is actually about

Three issues decide roof terrace applications, in this order of difficulty.

1. Overlooking of neighbouring gardens, balconies and habitable room windows from above fence height
2. Noise and disturbance from the use of the terrace, especially in the evening
3. The effect on the appearance of the host building, where railings, screens and access structures are visible from the street

Daylight and sunlight barely feature, which surprises people who expect an amenity issue to be an amenity assessment. A terrace is an open space rather than a built mass, so it obstructs almost nothing. The exception is the access structure, where a new stair enclosure or lift overrun on a roof can obstruct light to a neighbouring window, and that is assessed in the ordinary way against BRE guidance.

Overlooking from above the boundary

The reason a roof terrace is harder than a window is that the view moves. A window gives a view from one position, at one height, through a fixed aperture. A terrace gives a view from anywhere on it, from standing height above the parapet, across every boundary at once.

On a converted building in a terrace of houses, that usually means looking down into two or three rear gardens. Separation distances drawn from local design guidance, typically around 21 metres between facing habitable room windows, were written for windows and translate badly, so officers tend to assess terraces by drawing sightlines from the edges of the usable area.

Two practical consequences follow. The usable area has to be defined on the drawings, because an undefined flat roof is assessed as though all of it will be used. And set backs from the parapet do more work than any other single measure, because they cut the downward angle into gardens immediately below.

Screens, and designing them properly

A privacy screen has to be high enough to block the eye line of a standing adult, which puts it at roughly 1.7 to 1.8 metres above the terrace surface. Below that it is a balustrade.

What it is made of matters to the officer and to the occupier. Obscure glass keeps daylight into the terrace and the rooms behind it and looks transparent from the street, which can be an advantage on a modern building and a liability on a Victorian one. Slatted timber or metal reads better on a traditional rear elevation and blocks more light.

Three details decide whether a screen survives.

• It has to be fixed, not demountable, because a screen the occupier can take down is not mitigation
• It has to extend the full depth of the terrace on the flank, with no gap at the parapet end
• The specification on the drawing should state the obscurity level or the maximum gap between slats, so the condition can refer to something precise

Where the building is in a conservation area, the visibility of the screen from the street becomes the heritage question, and the answer is usually to set the whole arrangement back from the front and side parapets so nothing is seen from below.

Noise, and the conditions that follow

Noise from the use of a terrace is the issue that generates most objections after permission is granted, and it is the hardest to mitigate. Screens reflect and reduce very little. A group of people talking at roof level carries further than the same group at ground level, because there is nothing in the way.

Authorities deal with this through conditions. The realistic ones are:

1. A restriction on the hours during which the terrace may be used, often ending in the mid-evening
2. A limit on the number of people or a prohibition on commercial or event use
3. A restriction on amplified sound and on external lighting
4. A requirement that the terrace serves only the flat it is attached to, with no communal access

Hours conditions on a private residential terrace are difficult to monitor, and I would rather see a smaller, better-positioned terrace than a large one with a curfew nobody will police. Where the building contains several flats, a communal terrace with a management plan is actually easier to control than individual private terraces, because the managing agent has an enforceable mechanism.

An illustrative example

A three-storey end-of-terrace building converted to three flats, with a flat roof over a two-storey rear outrigger, and a terrace proposed for the first-floor flat. The usable area is drawn at 3 by 2.5 metres, set back 1.8 metres from the rear parapet and 1 metre from the flank, with 1.8 metre obscure screens on the flank and planters on the set back line. Separation to the facing rear elevation is 17 metres. The figures are illustrative.

That arrangement is arguable. The sightline from the back of the usable area is lengthened to something closer to the conventional separation, the side screens remove the downward view into the immediately adjoining garden, and the planters stop the furniture migrating to the parapet. A terrace covering the whole outrigger roof with a 1.1 metre glass balustrade would be refused on overlooking, and rightly.

What the application should contain

Drawings carry this, with the written case explaining them.

• A roof plan marking the usable area, the screens, the planters and the access door, with dimensions to each boundary
• Rear and side elevations showing the screens and how they meet the parapet
• At least one section through the terrace with a sightline drawn from standing height at the edge of the usable area to the nearest neighbouring boundary and window
• Photographs from the existing roof or the nearest upper window, which tell the officer more than any drawing
• Where an access structure is proposed, a daylight check on the nearest neighbouring window

Where a neighbouring window is close to a new stair enclosure or lift overrun, a Daylight and Sunlight Assessment against BRE guidance is the right document, and councils expect a suitably qualified author with professional review strongly advised. Where the terrace or its structures will cast shade onto a garden or a shared amenity space, an Overshadowing Study deals with that question directly.

Single-aspect flats in converted buildings often rely on exactly the elevation where the terrace is proposed, and the trade-off between outlook, light and privacy is covered in daylight to single aspect flats and how to fix them. How your authority applies the BRE numbers is set out in its own policy wording, which local plan amenity policies and how they use BRE 209 explains, and that is the first thing to read before commissioning anything.

Enter your postcode on PlanScope to see which supporting documents a conversion with a roof terrace is likely to need.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.