BREEAM HEA01 Daylight Calculations

Walker Energy Analysis carries out the daylighting assessment for BREEAM's HEA01 credit, using dynamic daylight modelling in IES Virtual Environment. Daylighting is worth up to two credits within HEA01, and the criteria have to be checked room by room against a specific average daylight factor and a uniformity requirement, not assessed by eye from the drawings.

How the Daylighting Assessment Works

The core metric is average daylight factor, the average daylight illuminance across a room's working plane, expressed as a percentage of the outdoor illuminance available at the same time. The minimum required average daylight factor depends on the building type and room use, and typically ranges from around 1.5% to 3%.

Meeting the average daylight factor alone isn't enough, the room also has to demonstrate reasonably even daylight distribution, not a bright patch near the window and a dark corner beyond it. This is checked through either a uniformity ratio of at least 0.3, or a minimum point daylight factor set at a fraction of the average daylight factor for that room type. Rooms with glazed roofs, such as atria, are held to a stricter uniformity requirement.

We model each relevant space using the building's actual window design, glazing specification, room geometry and internal surface reflectance, and report against whichever of the two uniformity routes suits the design.

• Average daylight factor calculation, room by room, using the building's actual glazing and geometry
• Uniformity assessment, using whichever of the two BREEAM routes best fits the design
• Reporting structured for your BREEAM assessor, room by room against the relevant thresholds
• Design-stage feedback where a space falls short, glazing area, room depth, or reflectance changes to bring it into compliance

Where Daylighting Sits Alongside Other Requirements

Daylighting is one part of BREEAM's wider HEA01 issue, which also covers glare control, view out and lighting controls, assessed separately. It's also worth checking early against a scheme's overheating strategy, since glazing decisions made to hit a daylight factor target can work against a TM52 or TM59 assessment, or vice versa, so the two are best considered together rather than in isolation.

Why Work With Us

We're a specialist energy consultancy. This is the core of what we do, not a sideline. Every assessment runs through IES VE as standard, we turn changes around quickly, and results come back in a format your team and BREEAM assessor can use immediately.

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