VSC — Vertical Sky Component

Vertical Sky Component assessment on a building

Obstruction & View

BRE standard obstruction assessment

The Vertical Sky Component (VSC) measures the proportion of the sky seen from the centre of a window — indicating how much potential daylight reaches it. The BRE recommends that a VSC below 27% (or less than 80% of its former value) signals a material loss of daylight.

DL-Light maps VSC values per window directly on the model, automatically flags BRE 209 guideline exceedances, and produces the compliance report — essential for planning applications and Rights of Light assessments in the UK.

VSC per window centre, mapped on the model
BRE 209 threshold check (27% and 80% original)
Rights of Light and planning assessment
Single-point calculation per window surface
Report with pass/fail per window

Frequently asked questions

What is Vertical Sky Component?

Vertical Sky Component (VSC) is the ratio of vertical illuminance at the centre of a window from a CIE overcast sky to the simultaneous unobstructed horizontal illuminance, expressed as a percentage. It measures how much sky is visible from a window and is used in BRE 209 / Rights of Light assessments in the UK.

What VSC value indicates a Rights of Light concern?

BRE 209 flags VSC values below 27% as potentially insufficient. A reduction of VSC to less than 80% of its previous value (a relative loss of more than 20%) is the threshold for a material loss in a Rights of Light assessment.

Is VSC the same as Daylight Factor?

No. VSC measures only direct sky visibility from the window plane and excludes internally reflected and externally reflected light, while DF includes all components inside a room. VSC is the standard for UK obstruction and Rights of Light analysis.

Going further

Read the full DL-Light user-guide reference for VSC — Vertical Sky Component: Windows guide · macOS guide.

VSC — Vertical Sky Component

BRE standard obstruction assessment

Frequently asked questions

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