Obscure glazing conditions on side facing windows
Obscure glass alone does not satisfy the condition. The window also has to be fixed shut below 1.7 metres, and an open casement overlooks just as well as a clear one.
An obscure glazing condition on an extension usually comes in two halves: the glass has to be obscured to a stated level, and the window has to be fixed shut below 1.7 metres above the floor of the room it serves. Both halves matter, and people comply with the first and ignore the second. A window with level 4 glass and a side-hung opening casement at 1.2 metres does not satisfy the condition, because an open window overlooks just as effectively as a clear one.
The 1.7-metre figure is not invented by councils. It comes from the permitted development rules themselves, and conditions on full applications borrow it because it is a known and tested number.
Why the condition is imposed
Side-facing upper floor windows look into next door's garden and often into next door's windows. Overlooking is a planning consideration, and the usual local guidance test is whether a habitable room window has direct views into a neighbour's habitable room or private amenity space at a distance the council considers unacceptable.
An obscure glazing condition is the standard answer because it lets the room keep daylight without the view. It is a proportionate control, which matters: a condition has to be necessary and reasonable, and refusing an extension outright over a landing window would fail that test where a glazing condition resolves the harm.
The corollary is that the condition attaches to the window's function. A bathroom or landing window is an easy case. A bedroom or living room window presents more difficulty, because obscure glazing in a principal habitable room reduces amenity for the occupier, and an officer may prefer that the window be moved or omitted.
Obscurity levels and what level is specified
The obscurity scale used across the glazing industry runs from 1 to 5, with 1 barely diffused and 5 giving no discernible image. Conditions commonly specify level 3 as a minimum, and level 4 or above where the relationship is close or the view is directly into a habitable room.
Two practical points follow. Specify the level on the drawings rather than waiting for the condition, because an approved drawing showing the level is easier to discharge than a condition requiring details to be submitted later. And remember the obscurity has to be in the glass, not applied to it. Adhesive film and etched vinyl are removable, so conditions are normally drafted to require obscure glazing rather than obscured glass, and a film will not discharge them.
Sandblasted and acid-etched glass are acceptable where the finish is integral. Reeded or patterned glass can be a good answer aesthetically on a period house, provided the obscurity level is adequate.
Fixed shut below a stated height
The opening restriction is measured from the internal finished floor level of the room the window serves, to the lowest part of the window that can be opened. Above 1.7 metres an opening light is permitted, because a person standing in the room cannot readily look down through it.
| Element | Requirement | Where measured |
|---|---|---|
| Glazing | Obscure to the specified level | The glass unit itself, integral not applied |
| Opening lights below 1.7m | Not permitted | Internal finished floor level to lowest openable part |
| Opening lights above 1.7m | Permitted | Same datum |
| Ventilation | Trickle or mechanical provision needed | Compliance with Approved Document F |
The ventilation consequence is real. A bathroom window fixed shut below 1.7 metres cannot provide purge ventilation, so mechanical extract becomes necessary. Coordinate that with the Building Regulations design rather than discovering it on site.
Top-hung lights with a high pivot are the usual solution where some opening is wanted. A tilt-and-turn unit is not, because the turn function opens from the bottom of the frame.
The condition in Class A for upper floor side windows
Paragraph A.3(b) of Class A, Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015 requires that any upper-floor window located in a wall or roof slope forming a side elevation of the dwellinghouse is obscure-glazed, and non-opening unless the parts that can be opened are more than 1.7 metres above the floor of the room in which the window is installed.
Class B, which covers roof additions such as dormers, carries an equivalent requirement for windows inserted in a wall or roof slope forming a side elevation. So a side-facing dormer window under permitted development is subject to the same rule whether or not anyone has told you.
Two consequences worth holding on to. Failing the condition does not make the extension partly unlawful, it removes the permitted development right for the whole enlargement, because A.3 conditions apply to the development as a whole. And because these are conditions attaching to the permitted development right rather than to a planning permission, there is no council decision to vary: either you comply or you need an application.
Where you are unsure whether the works as built comply, a Lawful Development Certificate under section 192 or section 191 of the Town and Country Planning Act 1990 is the only formal way to confirm that works are lawful.
Removing or varying the condition later
On a full planning permission, an obscure glazing condition can be varied or removed by an application under section 73 of the 1990 Act, which is determined as a fresh consideration of that condition. The authority is entitled to reach the same conclusion again, and a section 73 application that offers no change in circumstances will usually fail.
What does sometimes succeed is a change in the factual position. A new boundary treatment, an intervening extension next door that blocks the view, a change in the room's use from bedroom to store, or a redesign that raises the cill. Present the change with photographs from the neighbouring property's viewpoint if you can obtain them.
Replacing obscure glass with clear glass without permission is a breach of condition. Enforcement time limits for breaches of condition have been ten years, and the Levelling-up and Regeneration Act 2023 provides for a single ten-year period across the board, with the date it takes effect worth checking at the time. Buyers' solicitors ask about it, so it is a problem that surfaces at sale rather than immediately.
Rooflights as an alternative
A rooflight in the plane of the roof is often the better answer, and it avoids the argument entirely. Because the view from a rooflight is upwards and the cill is high, overlooking is rarely an issue, and daylight from a roof plane is more effective per square metre of glazing than daylight from a side window.
Three design points. Keep the cill at least 1.7 metres above the floor and the condition falls away in substance. Use a conservation-pattern rooflight, set flush with a central glazing bar, where the roof is visible from the street or the property is in a conservation area. And check the head height under the pitch, because a rooflight in a room with a low sloping ceiling can put the opening mechanism out of reach.
Our note on replacement windows in an unlisted period house covers the wider glazing detail questions, and glazed link extensions to a period house deals with the case where glazing is the main architectural move.
Showing compliance on the elevations
Make the drawings self-proving so the officer has nothing to ask.
- Annotate every side-facing window on the elevations with the obscurity level and whether it is fixed or opening
- Add a dashed 1.7-metre line on the internal elevation or section, dimensioned from finished floor level
- Include a window schedule listing reference, room served, glazing specification, opening type and openable height
- Show the ventilation provision for any room with a fixed window
- Mark the neighbouring windows and garden boundary on the block plan so the relationship is visible
Then explain the overlooking judgement in a short Design and Access Statement, with distances to the nearest neighbouring window and boundary. Where the relationship is contentious and policy is engaged, the argument belongs in a Planning Statement.
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. Enter your postcode to see which documents your extension is likely to need.
Frequently asked questions
What obscurity level do councils usually require?
Level 3 is the common minimum on the industry scale of 1 to 5, with level 4 or above where the window looks directly into a neighbour's habitable room or a close private garden. Specify the level on the elevations rather than waiting for a condition, because an approved drawing is easier to discharge.
Can I use privacy film instead of obscure glass?
No. Conditions are normally drafted to require obscure glazing rather than obscured glass, precisely because adhesive film and etched vinyl can be peeled off. Sandblasted or acid-etched glass is acceptable where the finish is integral to the unit, as is reeded or patterned glass of adequate obscurity.
Where is the 1.7 metre height measured from?
From the internal finished floor level of the room the window serves, to the lowest part of the window that can be opened. Top-hung lights with a high pivot satisfy it. A tilt-and-turn unit does not, because the turn function opens from the bottom of the frame.
Does a fixed window affect Building Regulations ventilation?
Yes. A window fixed shut below 1.7 metres cannot provide purge ventilation, so a bathroom or similar room will need mechanical extract. Coordinate that with the Approved Document F design at the same time as the planning drawings rather than discovering it during the fit-out.
Can an obscure glazing condition be removed later?
On a planning permission, by an application under section 73, which reconsiders that condition afresh. It succeeds where the factual position has changed, for example a new boundary treatment or an intervening extension next door, and generally fails where nothing has changed. Replacing the glass without permission is a breach of condition.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.