What the obscure glazing condition actually requires

The obscure glazing permitted development condition does not apply to every window in a side wall. Under Class A of Schedule 2 Part 1 to the Town and Country Planning (General Permitted Development) (England) Order 2015, paragraph A.3(b) catches any upper-floor window in a wall or roof slope forming a side elevation of the dwellinghouse. That window has to be obscure-glazed, and it has to be non-opening unless the parts that open are more than 1.7 metres above the floor of the room it serves. A ground-floor side window in a single-storey rear extension is not caught at all.

Where the condition bites

Three classes carry a version of the same condition, and they do not cover the same windows.

Class A, which covers enlargement and alteration of a house, applies it to upper-floor windows only. So a two-storey side or rear extension with a first-floor bathroom window in the flank wall is caught. A single-storey extension with a kitchen window in the same flank wall is not, however much the neighbour dislikes it.

Class B, the roof enlargement class that covers most rear dormers and hip to gable works, applies the condition to any window inserted on a wall or roof slope forming a side elevation. There is no upper-floor qualification, because by definition the work is in the roof. Class C, which covers other alterations to the roof including rooflights, carries the same requirement for a side roof slope.

What counts as a side elevation is a question of fact about the building, not about the boundary. A wall facing the garden of the house next door is not automatically a side elevation. The test is which elevation of the dwellinghouse the wall or roof slope forms, judged on the original house, and on a corner plot the answer is often contested.

What obscure glazing means when the Order does not define it

The Order itself gives no definition. The government's technical guidance on permitted development rights for householders explains obscure glazing as glass that prevents a view through, and points to a privacy level of 3 or above on the scale glass manufacturers publish as giving the necessary obscurity. Levels 1 and 2 blur a view without blocking it. Level 5 is almost opaque.

Specify the level, not the look. "Obscure glass" on a window schedule tells a case officer nothing, while "obscure glazing to privacy level 3" is checkable. Sandblasted and acid-etched glass can both reach that level, and so can patterned cast glass, which is what most bathrooms end up with anyway.

One quiet detail trips people up on dormers. The condition attaches to the window, so a dormer with a fixed obscure-glazed casement next to a clear-glazed opening light above 1.7 metres is compliant, while the same dormer with clear glass in the fixed pane is not.

Film and blinds are not compliance

The condition requires the window to be obscure-glazed. That is a property of the glass. Applied film is a surface treatment that can be peeled off in an afternoon, so it does not satisfy the condition, and neither does a blind, a frosted sticker or a planting screen outside.

Councils take this seriously because it is the one part of the condition that is easy to check from the street. Enforcement officers do look for the tell-tale bubbles and cut edges of film. And where film has been used instead of obscure glass, the consequence is not a notice about the window alone.

Measuring 1.7 metres from the right surface

The measurement runs from the floor of the room in which the window is installed to the lowest part of the window that can be opened. Not from external ground level, not from the window cill, and not from the floor below.

That matters in three situations. A room with a floor dropped below the general first-floor level gives you less height to play with than the elevations suggest. A split-level landing serving a side window sits between two floor levels, and the room the window serves decides the datum. And a top-hung window whose opening section starts at 1.65 metres fails the condition even though the handle is at 2 metres.

Where the number is tight, the usual fix is a fixed light with a separate high-level opening vent, or a trickle vent and mechanical extract so the window does not need to open at all. Building regulations ventilation requirements still have to be met, and they are assessed separately from the planning condition.

Rooflights in a side roof slope

A conservation rooflight in the flank slope of a hipped roof is the most commonly overlooked case. Class C permits alterations to a roof subject to limits on protrusion beyond the plane of the slope and on height relative to the highest part of the roof, and it carries the side-elevation obscure glazing condition.

Fitting a clear rooflight in a side slope therefore takes the whole alteration outside the class. Since rooflights are frequently installed by a roofer during a reroof with nobody consulting the Order, this surfaces years later during a sale.

What happens when the condition is not met

This is the part worth understanding before anything is ordered. A permitted development right is conditional. If a condition is breached, the development was never permitted development, so the entire extension or dormer is unauthorised rather than just the offending window. The council can act against the whole of it.

In practice an authority usually asks for the glazing to be changed, because that is proportionate and quick. The exposure is wider than that, though, and it reappears when a buyer's solicitor asks for evidence that the works were lawful. Time limits for enforcement against operational development in England were changed by the Levelling-up and Regeneration Act 2023, so check the current position rather than relying on the old four-year rule.

A Lawful Development Certificate under section 191 or 192 of the Town and Country Planning Act 1990 is the only formal way to confirm that works are lawful. Nothing else, including an email from a planning officer, binds the council. A supporting planning statement setting out which class is relied on and how each condition is met is what makes a certificate application straightforward rather than a conversation.

Put it on the drawings

Mark the window on the elevation and in the window schedule with both halves of the condition: the privacy level of the glass, and the height of the lowest opening part above finished floor level. Add the floor level as a figure on the section. It costs nothing at drawing stage and it answers the question a conveyancer will ask in ten years.

Other classes carry conditions that are just as easy to miss, such as the permeable surfacing requirement that governs front garden paving under Class F. The pattern is the same: the right exists, the condition is the price, and the condition is where the right is lost. You can browse the document types that support a householder application or a certificate if the works have already been done.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. Article 4 directions and designated land can remove or narrow these rights, so confirm what applies to your address. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. Enter your postcode on PlanScope to check which documents your works would need.