Daylight and sunlight.
Daylight is comfort, health and lower lighting energy. We model it properly, EN 17037 and climate-based, and we trade it against overheating in the same model, so more glass for daylight never quietly creates a summer overheating problem.
What daylight, sunlight and overheating analysis delivers.
What it isDaylight is not a soft benefit. It sets how a room reads, how alert the people in it stay, and how much electric lighting the building burns for the next sixty years. The same glazing that brings daylight in brings solar gain and the risk of summer overheating, so daylight has to be modelled and traded off, not guessed from a window schedule.
We assess daylight provision to EN 17037 and BS 8206, calculate the daylight factor, and run climate-based daylight modelling on a Radiance-class engine where orientation and real annual performance decide the answer. For planning we produce the BRE BR 209 daylight and sunlight study, including vertical sky component and rights to light for neighbours. Here is the part most teams split: daylight and overheating are modelled together, not handed to two consultants who never speak. The two are traded in one model, so more glass for daylight does not quietly cook the building in July.
On a Passive House or Passivhaus scheme the daylight strategy carries straight into the energy model held by your Passivhaus designer, so the facade that wins consent is the facade the building is built to deliver.
EN 17037 and BS 8206 for daylight provision, sunlight exposure, view and glare. Daylight factor and average daylight for quick comparison. Spatial daylight autonomy and annual sunlight exposure for real annual performance. BRE BR 209 for planning daylight and sunlight, with VSC, the no-sky line, APSH and rights to light for neighbours.
More glazing improves daylight and worsens solar gain. We trade glazing area, position, g-value and shading against daylight provision, space-heating demand and the CIBSE TM59 overheating result in a single exercise, so daylight is never bought at the cost of comfort or energy.
What we assess.
ScopeInterior daylight, sunlight, glare, the effect on neighbours and the daylight-against-overheating trade-off, all to the standards a planning officer and a building physicist both recognise. The first four lines below are the assessment. The last is the one most teams leave out.
Daylight provision to EN 17037 and BS 8206, the daylight factor and average daylight, and climate-based daylight modelling for spatial daylight autonomy where orientation and real annual performance matter.
Sunlight reaching the room and the amenity space, reported as annual probable sunlight hours, so a north-facing aspect or an overshadowing block is caught while the massing can still move.
Glare from direct sun and bright sky on the working plane and screens, assessed against EN 17037 protection from glare, so a daylit classroom or office does not force the blinds shut by mid-morning.
The effect on neighbouring windows to BRE BR 209: vertical sky component and the no-sky line for daylight, APSH for sunlight, and rights to light geometry where a legal interest is in play. The study a submission, an objection or an appeal needs.
Glazing area, position, g-value and shading traded against daylight provision, space-heating demand and the CIBSE TM59 overheating result together. Not daylight in one silo and overheating in another, found to disagree on site.
Method: how we work.
MethodWe fix the daylight target and the planning context with the design team: the EN 17037 and BS 8206 level the project aims for, the daylight factor a local authority expects, and any daylight and sunlight duty to neighbours under BRE BR 209. The brief is agreed before the facade is fixed, while glazing can still move and the answer is still cheap.
We build the model from the geometry and the site context, surrounding buildings included. The daylight factor is calculated where a simple comparison is needed; climate-based daylight modelling, with the local sky and a full year of weather, is run where orientation, glare and annual performance decide it. Sunlight access, APSH and the effect on neighbours, including VSC and rights to light, are assessed to BRE BR 209.
The daylight result is tested in the same model against the energy balance and the CIBSE TM59 overheating assessment. Where more glazing helps daylight but pushes a room into overheating, we resolve it with glazing position, a lower g-value, external shading or ventilation, and re-run all three until daylight, energy and comfort hold together. One trade-off, not two reports that contradict each other.
We issue the glazing ratios, g-values and shading the design needs to meet the daylight target, and the BRE BR 209 report a planning authority requires for a submission or an appeal. The numbers carry straight into the energy model and the construction specification, so the daylight that wins consent is the daylight the building is built to deliver.
Common questions.
FAQWhat is EN 17037 and how does it assess daylight?
EN 17037 is the European standard for daylight in buildings. Instead of a single daylight factor under an overcast sky, it judges the daylight a space receives across the whole year using the local sky and climate, and sets target illuminance over a share of the floor area for a share of daylight hours. It also covers sunlight exposure, view out and protection from glare. We model to EN 17037 and BS 8206 alongside the daylight factor and the BRE BR 209 metrics that planning officers still ask for, so one assessment satisfies both the standard and the local planning requirement.
What is the difference between daylight factor and climate-based daylight modelling?
Daylight factor is one ratio of internal to external illuminance under a standard overcast sky. It is quick, widely understood and still required by many planning authorities, but it ignores orientation, the real sky and the time of year. Climate-based daylight modelling runs the actual hourly weather and sky for the site through a Radiance-class engine to predict daylight across the year, reporting spatial daylight autonomy and annual sunlight exposure. We use the daylight factor where a simple comparison is needed and climate-based daylight modelling where orientation, glare and real annual performance decide the design.
Do I need a daylight and sunlight report for planning?
Often, yes. Many authorities want a daylight and sunlight assessment covering daylight and sunlight inside the proposed building and the effect on neighbours, assessed to BRE BR 209 using vertical sky component, APSH and rights to light. We produce the report the authority needs for the submission or the appeal, and because the same team holds the energy and overheating model, the daylight strategy that wins consent is the one that performs in use rather than a separate study that contradicts it.
How is daylight balanced against overheating?
In one model, which is the difference. More glass improves daylight and raises solar gain, so a scheme that fixes daylight in isolation can quietly create a summer overheating problem that a separate consultant only finds later. We trade glazing area, position, g-value and shading against daylight provision, space-heating demand and the CIBSE TM59 overheating result together, so the window that brings the light in does not cook the room in July. Daylight and overheating are never sized in separate silos.
Can you assess the effect on a neighbour for a rights to light or planning objection?
Yes. We assess the daylight and sunlight reaching neighbouring windows to BRE BR 209, using vertical sky component and the no-sky line for daylight and annual probable sunlight hours for sunlight, and we run the rights to light geometry where a legal interest is in play. The same study supports a planning submission, a response to an objection or an appeal, and the numbers are reported clearly enough to put in front of a planning officer or an inspector.
Get the daylight right early.
Tell us the scheme, the sector and where it sits in planning. We model daylight, sunlight and overheating together, so the facade works on all three before it is fixed. We do this most on schools, housing and the planning submissions and appeals that hang on the daylight numbers.