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PDFWAC 51-11C-40232

Section C402.4.2Minimum skylight fenestration area.

C402.4.2 Minimum skylight fenestration area. For single story buildings only, in an enclosed space greater than 2,500 square feet (232 m2) in floor area, directly under a roof with not less than 75 percent of the ceiling area with a ceiling height greater than 15 feet (4572 mm), and used as an office, lobby, atrium, concourse, corridor, gymnasium/exercise center, convention center, automotive service, manufacturing, nonrefrigerated warehouse, retail store, distribution/sorting area, transportation, or workshop, skylights are required to provide a total toplight daylight zone area not less than half the floor area and shall provide one of the following:
1. A minimum ratio of skylight area to toplight daylight zone area under skylights of not less than 3 percent where all skylights have a VT of at least 0.40 as determined in accordance with Section C303.1.3.
2. A minimum skylight effective aperture of at least 1 percent determined in accordance with Equation 4-5.
Skylight Effective Aperture
(0.85 x Skylight Area x Skylight VT x WF)/Daylight zone under skylight
(Equation 4-5)
Skylight area
Total fenestration area of skylights.
Skylight VT
Area weighted average visible transmittance of skylights.
Area weighted average well factor, where well factor is 0.9 if light well depth is less than 2 feet (610 mm), or 0.7 if light well depth is 2 feet (610 mm) or greater.
Light well depth
Measure vertically from the underside of the lowest point of the skylight glazing to the ceiling plane under the skylight.
Skylights above daylight zones of enclosed spaces are not required in:
1. Reserved.
2. Spaces where the designed general lighting power densities are less than 0.5 W/ft2 (5.4 W/m2).
3. Areas where it is documented that existing structures or natural objects block direct beam sunlight on at least half of the roof over the enclosed area for more than 1,500 daytime hours per year between 8 a.m. and 4 p.m.
4. Spaces where the daylight zone under rooftop monitors is greater than 50 percent of the enclosed space floor area.
5. Spaces where the total floor area minus the sidelight daylight zone area is less than 2,500 square feet (232 m2), and where the lighting in the daylight zone is controlled in accordance with Section C405.2.3.1.
C402.4.2.1 Lighting controls in daylight zones under skylights. Daylight responsive controls complying with Section C405.2.4.1 shall be provided to control all electric lights within daylight zones.
C402.4.2.2 Haze factor. Skylights in office, storage, automotive service, manufacturing, nonrefrigerated warehouse, retail store, and distribution/sorting area spaces shall have a glazing material or diffuser with a haze factor greater than 90 percent when tested in accordance with ASTM D 1003.
Skylights designed and installed to exclude direct sunlight entering the occupied space by the use of fixed or automated baffles, or the geometry of skylight and light well.
[Statutory Authority: RCW 19.27A.025, 19.27A.045, 19.27A.160, and 19.27.074. WSR 16-24-070, § 51-11C-40232, filed 12/6/16, effective 5/1/17. Statutory Authority: RCW 19.27A.025, 19.27A.160, and 19.27.074. WSR 16-03-072, § 51-11C-40232, filed 1/19/16, effective 7/1/16. Statutory Authority: RCW 19.27A.020, 19.27A.025 and chapters 19.27 and 34.05 RCW. WSR 13-04-056, § 51-11C-40232, filed 2/1/13, effective 7/1/13.]
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