Roof terraces, overlooking and privacy screens

A roof terrace raises an overlooking objection that a window of the same size would not, because the viewer can move. Standing at the parapet, a person on a terrace commands a continuous field of view across neighbouring gardens and into first-floor rooms, and they can choose where to stand. That is why officers treat terraces and balconies as a distinct amenity issue, why a privacy screen condition appears on so many consents, and why obscure glazing, which works for a fixed window, does nothing here.

If you are converting a flat roof over a rear extension or a commercial unit into private outdoor space, the design question is not whether the terrace is visible. It is where someone standing on it can see, and what stops them.

Why terraces are assessed differently from windows

Separation distance policies were written for windows. Many adopted local plans and design guides use a back-to-back figure in the region of 20 to 22 metres between facing habitable room windows, with a shorter distance to a blank elevation. Check the figure in your own adopted plan, because it is a local policy and the numbers differ.

Those distances assume a viewer standing inside a room, set back from the glass, looking out through a limited cone. A terrace removes all three assumptions. The viewer stands at the edge rather than behind it, the cone of view widens to most of a hemisphere, and the sense of being observed goes up because the observer is visible too. Perceived overlooking, not geometric overlooking, is what generates objections.

Terraces at height also create a downward view that no ground-level separation standard addresses. A terrace at second-floor level 15 m from a garden boundary looks directly into the most private part of that garden, which is usually the area closest to the house.

Standing eye height and the sight line that matters

Set the assessment at standing eye height, taken as roughly 1.6 m above the finished terrace surface, and draw the sight lines from the terrace edge rather than from its centre.

Two lines do most of the work. The first is from the nearest usable point on the terrace to the nearest neighbouring habitable room window. The second is from that same point to the neighbour's garden boundary, which tells you how much of the private garden falls within view. Draw both in section and in plan, and draw them from the worst case position, which is almost always the corner.

A screen works by interrupting the line. Its effectiveness depends on three things: its height above the terrace surface, its position relative to the viewer, and whether it is opaque. A 1.7 m screen at the terrace edge blocks a near-horizontal view. The same screen set 1 m inboard blocks less, because the viewer can approach and look over the top on a downward angle.

Glass balustrades are the common failure. Clear glass gives no privacy. Frosted or sandblasted glass obscures the viewer but does not stop them looking over a 1.1 m balustrade, because the balustrade is below eye height. If a screen is doing privacy work, it has to be above 1.7 m and it has to be solid or effectively so.

Screen height, opacity and material

A screen specification that an officer can condition has four parts: the height above the finished terrace surface, the extent along which it runs, the material, and the degree of obscuration.

Timber slatted screens with a gap are the usual compromise on appearance, and they are also the usual source of a later complaint, because a 20 mm gap at 1.5 m distance gives a usable view. If slats are used, specify the gap and the angle, or use a double-layer arrangement. Perforated metal is treated by its open area. Planting is a softening measure rather than a screen, since it is seasonal, it can die and nobody can condition its survival in a way that is enforceable in year fifteen.

Material choice also has to answer to the elevation. On a conservation area frontage a 1.8 m opaque screen above a parapet is often the thing that makes the scheme unacceptable in design terms, even though it solves the privacy point. Setting the terrace back behind the existing roof form, or taking it out of the front plane entirely, usually resolves both. The design reasoning belongs in the Design and Access Statement, with the sight line sections included rather than described.

Noise and use as a separate harm

Overlooking and noise are different objections and they need different answers.

A roof terrace concentrates outdoor activity at height, and sound from a raised source carries further than the same sound at ground level, with less screening from fences and vegetation. Where a terrace serves a flat above a commercial unit, or several flats share one, the noise case can be stronger than the privacy case. Conditions restricting hours of use are common, and sometimes a condition restricts the terrace to maintenance access only.

That last type needs care. A condition has to be necessary, relevant, enforceable, precise and reasonable. A condition preventing all recreational use of the only private outdoor space serving a dwelling is vulnerable, particularly where the adopted plan requires private amenity space. In London, policy D6 of the London Plan 2021 sets a minimum of 5 m2 of private outdoor space for one and two person dwellings, with 1 m2 for each additional occupant, so removing the terrace's function may put the scheme in conflict with the plan it is meant to satisfy.

An illustrative example

This example is illustrative. A two-storey rear extension to a Victorian terrace has a flat roof at first-floor level, 9 m from the rear boundary and 17 m from the facing houses. The owner applies for a terrace with a glass balustrade. The officer's concern is the downward view into both adjoining gardens at a distance of about 2 m from each boundary. The revised scheme sets the usable area 1.8 m in from each side boundary, puts 1.8 m obscure-glazed screens on both flanks for the full depth, keeps a clear balustrade only on the rear face and reduces the terrace depth so the nearest usable point is 11 m from the boundary. Both neighbours withdraw their objections.

Conditions, and designing a terrace that gets consent

Expect a condition requiring the screens to be installed before first use of the terrace and retained thereafter, with the specification approved in writing. Expect a second condition restricting any further openings or raised platforms.

Note: a raised platform exceeding 0.3 m in height is excluded from Class A of Part 1 of the GPDO 2015, and balconies and verandas are excluded too, so there is no permitted development route to a roof terrace on a house. Flats and maisonettes have no Part 1 rights at all.

Four design moves do most of the work on a scheme that has to get through:

• Set the usable area back from the boundary rather than screening at the boundary.
• Use the existing roof form to do the screening where you can, since an existing parapet costs nothing in design terms.
• Keep the terrace off the principal elevation, especially in a conservation area.
• Show the sight lines in section at 1:50 or 1:100 on the submitted drawings, so the officer does not have to construct them.

Amenity policies in local plans borrow heavily from daylight and sunlight practice even when privacy is the issue, and our note on local plan amenity policies and how they use BRE 209 explains where that leads. Where the terrace also affects light to neighbouring flats, the overlap is covered in daylight to single aspect flats and how to fix them, and a formal Daylight and Sunlight Assessment may be needed alongside the privacy case.

Draw the sight lines before you draw the screen. Enter your postcode on PlanScope to see which reports a terrace scheme on your building 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.