Daylight conditions and what they can secure

A planning condition can control the specification of a window, the depth of a reveal, whether an opening is fixed shut and the height at which obscure glazing starts. It cannot make a scheme daylight compliant after the fact. If the massing fails, no condition will rescue it, because a condition that requires an outcome rather than a specification fails the precision and enforceability tests and an inspector will strike it out on appeal.

That distinction governs everything worth saying about daylight conditions. Conditions secure the mitigation that the assessment has already shown works. They do not substitute for the assessment.

What a condition can and cannot achieve

The six tests in the Planning Practice Guidance on the use of planning conditions apply in full: necessary, relevant to planning, relevant to the development permitted, enforceable, precise, and reasonable in all other respects. Daylight and privacy conditions fail most often on precision and enforceability.

Conditions that hold up:

• Windows to be installed as shown on stated drawing numbers, including reveal depth and cill height.
• Named openings to be fitted with obscure glazing to a stated privacy level and to be non-opening below a stated height above internal finished floor level, and retained as such.
• Balcony screening to a stated height and opacity, installed before first occupation.
• Brise soleil, fins or external louvres provided in accordance with an approved detail.
• Removal of specified permitted development rights to insert new openings in a named elevation.

Conditions that do not hold up:

• A requirement that the development shall not cause unacceptable loss of daylight to neighbouring properties. Nobody can test compliance, so nobody can enforce it.
• A requirement to achieve stated vertical sky component or annual probable sunlight hours figures at a neighbour's window after construction, because the applicant has no control over the neighbour's property and no remedy if the figures fall short.
• A requirement to submit a further daylight assessment before occupation, where the purpose is to check whether the built scheme is acceptable. That defers the decision rather than conditioning it, and an inspector will treat it as evidence that the application should not have been approved.

Where the assessment has driven the design, say so in the committee report wording you suggest to the officer. Our note on presenting daylight results a committee can read covers how to set that out so the reasoning survives.

Glazing specification and reveal depth

Reveal depth and cill height change daylight results measurably, and they are the parameters most often lost between planning and construction. A 300 mm reveal modelled at planning stage becomes a 100 mm reveal once the contractor value-engineers the facade, and the vertical sky component at the affected rooms drops with it.

The fix is a condition tying the elevations and the bay detail together. Cite the general arrangement elevation and the window detail by number, and add that the reveal depth shall not be reduced without the prior written approval of the local planning authority. That is precise, enforceable against the developer and directly relevant to the permission.

For the receiving windows within your own scheme, the same logic applies in reverse. Where compliance with the BRE 209 criteria depends on a light shelf, a reflective soffit or a specified glazing transmittance, name the value. A condition that refers to "high performance glazing" secures nothing, because every product claims it.

Obscure glazing and fixed shut openings

The standard privacy condition has three limbs, and all three are needed:

1. The opening is identified by reference to a drawing and a window reference, not by description.
2. The glazing is obscure to a stated privacy level, which is measurable against manufacturers' published scales.
3. The opening is non-opening below a stated height, conventionally 1.7 m above internal finished floor level, so that it cannot be used for overlooking, and the arrangement is retained thereafter.

Leave out the third limb and the occupier fits a clear opening light within a year. Leave out the second and you get frosted film on the inside of the glass, which comes off.

A practical caution. Obscure glazing to a habitable room reduces the daylight reaching it, so a privacy condition applied to a bedroom window can create an internal daylight problem in the same scheme. Where the room has only one window, solve the privacy issue with orientation, screening or a recessed opening rather than with obscure glass.

Restricting future permitted development windows

Inserting a window in a dwellinghouse is generally permitted development, which means a privacy mitigation designed into the scheme can be undone lawfully after occupation. A condition removing that right is the answer, and the Planning Practice Guidance treats such conditions as the exception rather than the rule.

To make one stick:

• Limit it to the elevation or elevations where the harm arises, not to the whole building.
• State the class being removed, referring to Schedule 2 of the General Permitted Development Order 2015.
• Give a reason that identifies the specific harm and the policy it engages.

A blanket condition removing all permitted development rights from a new dwelling is unreasonable and will be deleted on appeal. A condition removing the right to insert openings in the flank elevation facing a neighbour at first floor level, because that elevation is within a short distance of habitable windows, is defensible.

For flats and other buildings that are not dwellinghouses, the householder classes do not apply in the first place, so a condition on openings usually works through the approved drawings instead.

Conditions on internal layouts

Internal layouts can be secured by condition referencing the approved floor plans, and they routinely are in schemes where daylight compliance depends on which rooms face which elevation.

The weakness is what happens next. Internal alterations to a dwelling are not usually development, so once the flat is occupied a resident can convert a study into a bedroom without needing anything from the council. A scheme whose daylight case rests on a particular room being non-habitable is fragile by design, and an officer who notices will say so.

Where the point cannot be avoided, two things help. Condition the layout by drawing number and add that the rooms labelled as non-habitable shall not be used as bedrooms or living rooms without prior written approval, which at least creates an enforceable planning control. And be candid in the Daylight and Sunlight Assessment about how much of the compliance case depends on that labelling.

Pre-commencement against pre-occupation

Most daylight and privacy conditions belong at pre-occupation or as compliance conditions, not pre-commencement.

Section 100ZA of the Town and Country Planning Act 1990 and the Town and Country Planning (Pre-commencement Conditions) Regulations 2018 require the applicant's written agreement before a pre-commencement condition can be imposed, subject to the notice procedure. So an officer who drafts a pre-commencement condition for a glazing schedule has created a delay for themselves as well as for the developer.

Sensible allocation:

"Before the relevant part is constructed" is the wording that solves most facade details. It avoids the pre-commencement procedure while still catching the detail before it is built.

Drafting a condition the officer will accept

Give the officer the words. A suggested condition in the covering letter, drafted to the six tests, is accepted far more often than a complaint about a draft condition after committee.

A workable pattern: the trigger, the obligation, the specification with measurable parameters, the retention requirement, then the reason with the policy reference. Keep each condition to a single obligation, because a condition bundling three requirements together is harder to discharge and harder to enforce.

Two habits worth adopting. Ask for the glazing schedule to be a named document rather than a description in the condition text, so it can be updated by agreement without a section 73 application. And check whether an Overshadowing Study is the better vehicle for amenity space effects, since sunlight to gardens and courtyards is rarely well handled by window conditions. The circumstances in which the wider assessment is needed at all are set out in our note on when a daylight and sunlight assessment is required.

This is general guidance, not legal advice. Condition wording turns on the facts of the permission and the adopted policy, so check the position with your local planning authority or take advice from a qualified professional.

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