This measure can be claimed if the top floor of a building utilizes natural daylight from skylight(s) to light up the top floor of the interior, reducing the use of artificial lighting during daytime hours.
The intent of this measure is to reduce the use of electricity for artificial lighting by using natural daylight. The use of daylight for lighting interior spaces requires only a part of the roof to be transparent, and can save significant amounts of electricity usage for lighting, especially in spaces that are used mostly in the daytime.
The skylight(s) must be well distributed to provide maximum daylight penetration in the building. The skylight(s) may be horizontal or vertical (also called roof monitor).
To claim this measure, the design team must demonstrate that transparent elements in the roof allow sufficient daylight to achieve the required lighting level in the interior of the space of the top floor area, and that the lights in this area are equipped with dimming or shut-off controls such as daylight-responsive controls.
The “Daylight Zone” claimed under each type of skylight must comply with the guidelines accompanied by the figures below.
- The Daylight Zone of a skylight shall extend in both horizontal directions along the floor beyond the edge of the skylight to the lesser of (i) 0.7 x the ceiling height, or (ii) the nearest obstruction that is 0.7 times the ceiling height or more, as indicated in Figure 16.
- An obstruction less than 0.7 x the ceiling height (CH) may be ignored
- An obstruction up to 0.7 x CH in height that is closer than 0.7 x (CH minus the obstruction height (OH)) may be ignored
- In the case of multiple skylights, the floor areas under the skylights which are being counted as Daylight Zone areas must not overlap.
- The lighting in each Daylight Zone area must be controlled with either manual or daylight-responsive controls. Controls or calibration mechanisms must be readily accessible, and may serve all light fixtures, alternate fixtures or individual fixtures in a zone. Dimmable controls must be capable of dimming to 15% of light output or lower and be capable of complete shut-off. Exceptions:
- Areas with less than 6.5 Watts/m2 of general lighting may not be controlled
- Areas designated as security or emergency areas that are required to be continuously lighted
- Interior exit stairways, interior exit ramps and exit passageways
- Emergency egress lighting that is normally off
- Display/accent lighting must have dedicated controls independent of the general lighting controls
Sunlight access must not be blocked for > 1500 hours in a year between 8 a.m. and 4 p.m.
One method to verify the adequacy of the daylighting system is to calculate the product of the visible transmittance (VT) of the skylight and the area of the skylight (rough opening), divided by the area of the Daylight Zone. The result must be no less than 0.008.
Figure 16. Daylight zone under roof skylights
Figure 17. Daylight zone under a vertical skylight (roof monitor) with a flat top
Figure 18. Daylight zone under a vertical skylight (roof monitor) with a sloping top
Natural daylight can be introduced into the top floor using windows in the roof, that is, skylights. Glass skylights are typically used, but daylight can also be introduced through other transparent or translucent materials such as translucent insulation panels.
Relationship to Other Measures
The use of skylights will impact the heat gain through a roof which will impact the energy use for space conditioning. The area of skylights and their thermal properties (the Solar Heat Gain Coefficient or SHGC and the U-value) must be optimized to avoid excessive heat gain. Reduction in electricity usage for artificial lighting by using skylights must be balanced with the potential increase in cooling energy use.
The base case assumes no skylights in the building. When this measure is selected, the improved case with skylights assumes that a default area of 50% of the top floor is a Daylight Zone served by skylights, with a default Solar Heat Gain Coefficient (SHGC) of 0.35 and a U-value of 1.7 W/m2 .K. Selecting the measure also reveals the editable fields for (1) the area of the Daylight Zone (represented as a percentage of the top floor area) labelled as “% Day Lit Area,” (2) SHGC of the fenestration, and (3) U-value of the fenestration.
|Design Stage||Post-Construction Stage|
At the design stage, the following must be used to demonstrate compliance:
At the post-construction stage, the following must be used to demonstrate compliance:
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