808.3 Daylit Area of Building Spaces
|Required daylit area ≥ 25% × TDP||(Equation 8-1)|
The total daylight potential (TDP) is a weighted average of the individual daylight potentials for each floor:
|TDP||=||Σ(DP1 ÷ FA1/TF) + (DP2 ÷ FA2/TF) + …|
For floors with roof area immediately above:
|DP1, 2 ...||=||1 — [(OW1/TW1) × (OR1/TR1)]|
For floors without roof area immediately above:
|DP1, 2 ...||=||1 — (OW1/TW1)|
|OW1, 2 ...||=||The length of obstructed exterior wall for each floor that does not face a public way or a yard or court complying with Section 1206 of the International Building Code or where the distance to any buildings, structures, or geological formations in front of the wall is less than two times the height of the buildings, structures, or geological formations. For the purposes of this determination, the maximum allowed heights of buildings or structures on adjacent property under existing zoning regulations is permitted to be considered.|
|TW1, 2 ...||=||The total length of exterior wall for each floor.|
|OR1, 2 ...||=||The roof area immediately above each floor that is shaded during the peak sun angle on the summer solstice by permanent features of the building, or by permanent features of adjacent buildings.|
|TR1, 2 ...||=||The total roof area immediately above each floor.|
|FA1, 2 ...||=||The total floor area of each floor.|
|TF||=||The total building floor area.|
|EA = (AF × VT)/DA||(Equation 8-2)|
|AF||=||Area of fenestration.|
|VT||=||Visible transmittance of the fenestration.|
MINIMUM EFFECTIVE APERTURE
|SKY TYPE||MINIMUM EFFECTIVE APERTURE |
|Sidelighting from fenestration in a wall |
[see Figure 808.3.1.1(1)]
|Sidelighting from rooftop monitor [see |
Figures 808.3.1.1(2) and 808.3.1.1(3)]
|Toplighting (see Figure 808.3.1.2)|
- Sky Type A — more than 75 percent mean sunshine, in accordance with the NOAA Annual Mean Sunshine Percentage Table.
- Sky Type B — 45 percent to 75 percent mean sunshine, in accordance with the NOAA Annual Mean Sunshine Percentage Table.
- Sky Type C — less than 45 percent mean sunshine, in accordance with the NOAA Annual Mean Sunshine Percentage Table.
- Sky conditions shall be assumed to be clear.
- Address the effects of exterior shading devices, buildings, structures, and geological formations on the fenestration of the proposed building and on the ground and other light reflecting surfaces. Include the effects of movable exterior fenestration shading devices. The configuration of fenestration with automatically controlled variable transmittance shall be adjusted to accurately represent the control system operation.
- Exclude the effects of interior furniture systems, shelving, and stacks.
- Use the actual reflectance characteristics of all materials.
- Where blinds, shades and other movable interior fenestration shading devices are included in the analysis and the exact properties of such devices cannot be accurately modeled, such devices shall be assumed to be completely diffusing, with a visible transmittance of 5 percent for fabric shades, and 20 percent for horizontal or vertical blinds.
- Calculation points shall be spaced not more than 39.4 inches (1 m) by 39.4 inches (1 m). The calculation grid shall start within 20 inches (508 mm) of each wall or partition.
- Where details about the window framing, mullions, wall thickness and well depth cannot be included in the model, the visible transmittance of all fenestration shall be reduced by 20 percent.