> 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/user-guide/2d-building/envelope/skylights.md).
# Skylights
A skylight is a part of the building envelope and is a window-like element placed on the roof of a building to allow natural light to enter the space from above.
Skylights can be added to any roof surface to be considered in energy or daylight modelling. Where compliance calculations are being undertaken, the Reference Building skylight is nominated as per the local Building Code. See [Add Skylights](/user-guide/2d-building/building/levels/roof-geometry/add-skylights.md) for more information on drawing and geometry.
### Specify a Skylight
To specify a skylight, navigate to the 'Envelope' settings in the left panel and select 'Skylights'. Next, set the 'System U-value' or 'System R-value', as locally applicable, the System SHGC and VLT and hit 'Save'. You can also use 'Tags' to nominate different specifications if more than one skylight specification is within the design.
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