J1.4 Roof lights, or more commonly known as skylights, are also provided with a minimum thermal performance within NCC 2019 – J1.4. Such roof lights are defined as:
“a skylight, window or the like installed in a roof (a) to permit natural light to enter the room below; and (b) at an angle between 0 and 70 degrees measured from the horizontal plane.”
Setting a limit of 5% of the floor area in which the roof light serves to provide daylight too, transparent and translucent elements including any imperforate ceiling diffuser, Total system U-Value must not more than U3.9 W/m².K, while the Total system SHGC is set by the following:
|
Roof light shaft index |
Total area of roof lights up to 3.5% of the floor area of the room/space |
Total area of roof lights more than 3.5% and up to 5% of the floor area of the room/space |
|
< 1.0 |
≤ 0.45 |
≤ 0.29 |
|
≥ 1.0 < 2.5 |
≤ 0.51 |
≤ 0.33 |
|
≥ 2.5 |
≤ 0.76 |
≤ 0.49 |