How much glazing is enough?
For 100% daylighting from traditional skylights approximately 5% of roof area should be in skylights, (5% Skylight-to-Roof Ratio or SRR). The skylight specifications depend on climate. All climates should have high visible transmittance (Tvis or VLT). Hot climates should have low SHGC.
How to Size a Rectangular Skylight?
Area of one skylight = (Floor to Ceiling Height x 1.5) ^2 x SRR. Choose a size that is appropriate. Start with 5% SRR and modify depending on climate and building use. For example with a 12' ceiling and 5% skylight to roof ratio the right size skylight would be approximately: (12 x 1.5)^2 x 5% = 16.2sf. Therefore the project should use 4'x4' or 8'x2' skylights for good light distribution.
Tubular skylights: require a much lower SRR than traditional skylights, approximately 1-2%.
Tubular Skylight spacing guidelines: The following spacing criteria (from a tubular skylight manufacturer) are intended to provide uniform distribution of daylighting. MH refers to the mounting height of the diffuser above the work plane.
Enclosed and Open Plan Spaces:
From Walls: Spacing >0.5 x MH (1.0 x MH = Maximum)
Between Units: 1.0 x MH < Spacing < 1.3 x MH (Max. Spacing = 1.5 x MH)
Open Ceiling Spaces:
From Walls: Spacing >0.5 x MH (0.8 x MH = Maximum)
Between Units: 0.8 x MH < Spacing < 1.3 x MH (Max. Spacing = 1.5 x MH)
U-value: is more important in cold climates and has energy and condensation implications—the lower the U-value the greater the insulation value.
Dampers: used to darken space, are available with most skylights.