Obscure glazing conditions and the 1.7 metre rule
The 1.7 metre figure is a condition in the General Permitted Development Order, measured from internal floor level. Restricted opening hardware does not satisfy it, and a side bedroom window can fail Part B as a result.
The 1.7 metre figure comes straight out of the General Permitted Development Order, not from a council's design guide. Condition A.3 of Schedule 2 Part 1 Class A of the Town and Country Planning (General Permitted Development) (England) Order 2015 says that any window inserted in a wall or roof slope forming a side elevation of a dwellinghouse must be obscure-glazed, and must be non-opening unless the parts that can be opened are more than 1.7m above the floor of the room in which the window is installed. The same wording appears in the conditions attached to Class B roof extensions.
The measurement is taken from the internal finished floor level of the room, not from ground level outside. That single point causes more confusion than any other part of the householder permitted development rules, because an installer measuring up from the garden will put the opening light in the wrong place.
Where the figure applies and where it does not
Permitted development conditions and planning conditions are different animals that happen to use the same number. Under Class A, the obscure glazing requirement is automatic: get it wrong and the whole extension falls outside permitted development, which means the development is unauthorised rather than merely in breach of a condition. That is a much worse position to be in.
Where you have planning permission instead, the 1.7m figure is a convention that officers have borrowed from the Order. A condition on a full or householder permission can set a different height, apply to rear as well as side windows, or require obscure glazing on a first floor window that looks into a neighbour's garden at close range. The council has to justify it against the six tests in Planning Practice Guidance on the use of planning conditions, so the condition must be necessary, relevant to planning and to the development, enforceable, precise and reasonable in all other respects.
Side elevation means the elevation facing a side boundary. A window in a rear elevation is not caught by condition A.3, however directly it looks into next door. That is why so many extension disputes are about a rear window that the owner was told needed nothing and the neighbour expected to be obscured. Where overlooking from a rear window is the issue, the answer lies in privacy and overlooking distances between dwellings rather than in the glazing specification.
Obscure to what level
The Order says obscure-glazed and stops there. It does not define a degree of obscuration, which leaves room for argument when somebody installs lightly patterned glass that you can see shapes through.
Glass manufacturers grade patterned and textured glass on a five-point obscuration scale, where 1 is barely obscured and 5 is close to opaque. Councils that know their business condition a level, and level 3 or above is the common requirement for a window where privacy is the point. Some authorities also rule out films and sandblasting applied to clear glass, because a film can be peeled off and the control disappears with it.
- Specify the obscuration level on the elevation drawing and in the window schedule, not in a covering letter
- Say whether the obscuration is in the body of the glass or applied as a surface treatment
- State the cill height above internal finished floor level for each affected window
- Show the opening light position in section where the 1.7m line is close
Where the window serves a bathroom or a landing there is rarely any argument. Where it serves a bedroom or a study, the owner wants a view and the obscuration level becomes the negotiation.
Non-opening against restricted opening
The Order gives two options and they are not interchangeable. Either the whole window is fixed shut, or the openable parts sit entirely above 1.7m from the floor. A window with a top-hung fanlight whose lowest opening edge is at 1.6m does not comply, even though the handle is higher than that.
Restricted opening hardware is a different idea again. A restrictor that limits a casement to 100mm of travel satisfies some councils' conditions where the condition is drafted in those terms, but it does not satisfy condition A.3, because the restricted part is still an openable part below 1.7m. Restrictors can also be removed. If you are relying on permitted development, the fixed light or the high-level opening light are the only two safe answers.
| Arrangement | Compliant under Class A condition A.3 | Note |
|---|---|---|
| Fixed obscure glazed window, any height | Yes | Ventilation must come from elsewhere |
| Top-hung light with opening edge above 1.7m | Yes | Measure from internal floor level |
| Casement with restrictor, cill at 900mm | No | Openable part sits below 1.7m |
| Obscure glazed window with clear top light at 2m | Yes for opening, no for glazing | All of the window must be obscure glazed |
| Rooflight in a side-facing roof slope | Yes if obscure and high level | Class B conditions apply in the same terms |
Escape windows and the conflict with Part B
This is the practical trap on a loft conversion or a side extension that contains a bedroom. Approved Document B expects an escape window serving a habitable room in a loft or upper storey to have its openable area positioned with the bottom of the opening no more than 1.1m above the floor. A side-facing window that must be non-opening below 1.7m cannot do that job.
Where the only window in a new bedroom faces the side boundary, you therefore need either a second window in another elevation, a rooflight that can serve as the escape opening, or a protected stair enclosure with fire doors so that no escape window is needed. Designing the glazing specification without checking the escape strategy produces a room that complies with planning and fails building control, and the usual fix on site is an expensive one.
Conditions on new and existing windows
A condition can require obscure glazing in a window that forms part of the development. It cannot usually require you to alter an existing window that has nothing to do with the proposal, because the condition would not be relevant to the development permitted. Where an officer proposes exactly that, say so during the application rather than accepting it and arguing later.
There is a middle case. Where an existing window is being retained but the development changes the relationship, for instance a new first floor extension that brings an existing landing window much closer to the boundary, a condition touching that window can be justified. The test is whether the requirement is fairly and reasonably related to the development.
If you want a condition changed after permission is granted, the routes are an application under section 73 of the Town and Country Planning Act 1990 to vary or remove it, or a non-material amendment under section 96A where the change is minor in substance. A section 73 application attracts a fee and is publicised, so neighbours get another say. Removing an obscure glazing condition on that route is rarely straightforward where the original objection was about overlooking, and a short Planning Statement explaining what has changed is worth more than a one-line covering email.
Enforcing the condition years later
Obscure glazing conditions run with the land. A buyer who replaces the patterned glass with clear glass five years after occupation is in breach, whether or not they knew the condition existed, and the local planning authority can serve a breach of condition notice under section 187A of the 1990 Act. There is no right of appeal against a breach of condition notice, which makes it a sharper tool than an enforcement notice.
The Levelling-up and Regeneration Act 2023 extended the enforcement time limit in England to ten years for all breaches of planning control, so a glazing change is not quickly immune. Check when that change came into force before relying on any time limit, because the transitional arrangements matter for breaches that began earlier.
Most of these disputes start with a neighbour's complaint rather than a council inspection. If you are the neighbour, photograph the window, note the date, and report it to the enforcement team with the application reference and the condition number. If you are the owner, keep a copy of the approved window schedule with the deeds, because the next buyer's solicitor will ask.
Drawings that avoid a dispute
Almost every argument about obscure glazing could have been prevented by a better set of drawings. Mark each window on the proposed elevations with a reference, then provide a schedule listing the room served, the opening type, the cill height above internal finished floor level, the height of the lowest openable edge, and the obscuration level. Draw a section through any window where the 1.7m line is within 200mm of the opening light.
Where overlooking is the reason the glazing is being conditioned, it is worth testing whether the window is needed at all. A high-level clerestory, a rooflight or a reorganised internal layout often delivers better daylight than an obscured side window, and a Daylight and Sunlight Assessment can show that the room still works. Where a neighbour has objected on light rather than privacy grounds, the approach in answering a neighbour's daylight objection applies instead.
This is general guidance, not legal advice. A Lawful Development Certificate is the only formal way to confirm that works are lawful, so check the position with your local planning authority or a qualified professional before relying on it.
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Frequently asked questions
Is the 1.7 metres measured from the floor or the ground?
From the internal finished floor level of the room in which the window is installed, as condition A.3 of Schedule 2 Part 1 Class A of the GPDO 2015 states. Measuring up from external ground level is the most common error on site, and it puts the opening light below the permitted height on a sloping plot.
Does a window restrictor satisfy the obscure glazing condition?
Not under the permitted development conditions. Those require the window to be non-opening unless the openable parts are more than 1.7m above floor level, and a restricted casement still has an openable part below that line. Some planning conditions are drafted to accept restrictors, so read the wording of the condition itself.
What level of obscure glazing do councils require?
The Order does not define a level, so authorities commonly condition a minimum obscuration level on the glass manufacturers' five-point scale, often level 3 or above. Many also exclude applied films and sandblasting, because a film can be removed later. Put the level on the elevation drawing and in the window schedule.
Does the rule apply to rear windows?
No. Condition A.3 applies to windows in a wall or roof slope forming a side elevation of the dwellinghouse. A rear window overlooking a neighbour's garden is not caught, which is why separation distances and window positions do the work on rear elevations rather than the glazing specification.
Can I change the glass to clear after moving in?
Not without varying the condition. An obscure glazing condition runs with the land and binds later owners, and the council can serve a breach of condition notice under section 187A of the Town and Country Planning Act 1990, against which there is no right of appeal. Apply under section 73 if you want the condition changed.
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.