> For the complete documentation index, see [llms.txt](https://docs.betterbuilding.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.betterbuilding.io/sign-up-and-plans/news-and-updates/2026/bess-10-spatial-daylight-autonomy.md).
# BESS-10: Spatial Daylight Autonomy
BESS-10 introduced this new apartment daylight pathway on 23 November 2025, adding spatial daylight autonomy as a compliance option. Yes, we are a little slow on this one.
In the words of the BESS-10 administrators, quoted directly from the tool documentation.
> *Where spatial daylight autonomy is the chosen metric, provide daylight modelling using third party software. Modelling should be conducted to all main living areas and secondary habitable rooms of varying orientation and configuration. See the daylight modelling parameters in this section for more information.*
Full source,
At a high level, these new spatial daylight autonomy provisions check whether habitable rooms in a dwelling get enough natural light, since poor daylight access affects both comfort and reliance on artificial lighting, which ties into energy use elsewhere in the scorecard. It works by splitting rooms into two tiers and testing each against daylight thresholds, one for main living areas and one for secondary spaces, covered in detail below.
If you've chosen spatial daylight autonomy as your metric, you're signing up for third party daylight modelling. It needs to cover every main living area and every secondary habitable room, across whatever mix of orientations and configurations your design throws at it. See the modelling parameters below for the fine print.
There are two thresholds to know, both measured against winter daylit hours.
* **Adequate daylight** = at least 200 lux for half of winter daylit hours (1 June to 31 August)
* **Visual acuity daylight** = at least 50 lux for three quarters of winter daylit hours (same window)
"Visual acuity" needs less lux than "adequate." It comes down to duration versus intensity, and it trips people up more often than it should.
## Main Living Areas
The first job is working out which of your main living areas fall inside the "single-metric bounds." Everything that qualifies goes in one bucket, everything that doesn't goes in another. The bucket you land in changes how much modelling you actually owe.
### Inside the single-metric bounds
A room clears the single-metric bounds if it ticks all of these.
* Room depth from glazing is 9.0m or less
* Any balcony overhang beyond the glazing is 3.6m deep or less
* Glazing VLT is 0.35 (35%) or higher
* Building height is 36m or less
* At least 90% of the room has a direct line of sight to glazing
Meet all five, and you get a nice little shortcut. If adequate daylight reaches at least half the room's floor area, visual acuity daylight to at least 90% of the floor area is assumed to follow. You don't need to model it separately.
### Outside the single-metric bounds
Miss any of those five criteria and the shortcut disappears. Both adequate daylight and visual acuity daylight need to be modelled directly for that room.
And if none of your main living areas fall outside the bounds, this whole question becomes Not Applicable.
### What you need to answer
Unless you've landed on Not Applicable, you need a "Yes" to both of these to score any points in IEQ 1.5.
1. Does every main living area within the single-metric bounds achieve adequate daylight to at least 50% of its floor area?
2. Does every main living area outside the single-metric bounds achieve adequate daylight to at least 50% of its floor area, AND visual acuity daylight to at least 90% of its floor area?
Two yeses gets you 66% of IEQ1.5.
To push past that, there's one more question worth paying attention to. Across all your main living areas, what's the lowest percentage of floor area achieving adequate daylight in any single room? Answer above 50% here and you pick up additional points. Your worst-performing room is effectively setting your ceiling, so design accordingly.
## Secondary Habitable Rooms
Secondary rooms get an easier ride, since nobody's reading a novel in a walk-in robe. The rules are these.
* Only adequate daylight to 50% of floor area is tested. No visual acuity check here.
* Only 80% of rooms need to pass, not 100% like main living areas get in IEQ1.5.
* Every room, no exceptions, still needs to clear a lower bar, adequate daylight to at least 25% of floor area.
To work through this, follow these steps.
1. Model every secondary habitable room and check which ones hit adequate daylight to 50% of floor area.
2. Calculate the pass rate, the number of rooms meeting the criteria divided by the total number of secondary habitable rooms.
3. Separately, confirm every single room clears the 25% floor.
Two different bars, two different rulesets. Worth double checking you haven't mixed them up before submitting.
## Daylight Modelling Requirements
For multi-residential developments, model every habitable room across your range of orientations and configurations. For non-residential developments, model every occupiable area except ancillary spaces, no one's demanding daylight modelling for the server closet.
Your modelling report, submitted alongside the BESS report, needs to include the following.
* Modelling software, version, and release date
* Location and coordinates
* Time of year and time of day
* Sky conditions
* Orientation
* Visible Light Transmission (VLT) for every piece of glazing modelled
* Reflectance surface properties
* For open plan living areas, model the lounge, dining, kitchen, and any circulation space not separated by a wall, door, or opening. Treat it as one continuous space, because that's how people actually live in it.
* A results table listing room name/number, floor area (sqm), floor area above the minimum daylight metric (sqm), and the percentage of floor area meeting the metric
* 3D views covering all elevations, showing that shading devices and adjoining buildings are actually in the model
* Adjoining buildings modelled to their likely developed form based on current zoning (mirrored where relevant). If future development on neighbouring lots is uncertain, check with the council rather than guessing.
* Daylight contour plots (heatmaps) overlaid on the architectural plans, so the daylight penetration claims can actually be verified visually and not just taken on faith
One important note on scope, this is a check on built form, not interior design. Leave out furniture, vegetation, artwork, and rugs, indoor or outdoor. The model should reflect the building doing (or not doing) its job, nothing else.
### Modelling parameters
#### **Grid and material settings**
| Parameter | Value |
| ------------------------------------------------------------------ | ----------------------------------------- |
| Grid plane | Horizontal |
| Grid height level | 0.85m above finished floor level |
| Grid resolution | 0.5m x 0.5m (maximum) |
| Grid offset from internal walls | 0.00m |
| Reflectance, interior floors (and floor of private open space) | 0.30 |
| Reflectance, interior walls | 0.70 |
| Reflectance, ceiling | 0.80 |
| Reflectance, external surfaces (except ground and lightwell walls) | 0.30 (approximates an average brick wall) |
| Reflectance, external lightwell walls | 0.40 (approximates off-form concrete) |
| Reflectance, external ground surface | 0.10 (approximates asphalt) |
| Diffuse reflectance, translucent glazing | 0.07 |
| Diffuse transmittance, translucent glazing | = VLT (Visible Light Transmittance) |
| Specular transmittance, translucent glazing | 0.00 |
### **Occupancy schedule**
| Setting | Value |
| ------------ | ------------------------------ |
| Time of year | 1 June to 31 August |
| Days | 7 day week |
| Time period | 9:00 to 17:00 inclusive, daily |
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