# J4D5 Roof Lights

## What is J4D5 Roof Lights?

J4D5 Roof lights outlines the thermal performance requirements for roof lights or skylights based on the following requirements:

**Total Area**:

* Roof lights must not exceed 5% of the total floor area of the room or space they serve. This limitation helps control heat gain and loss.

**Combined Performance of Transparent and Translucent Elements**:

* **Total System SHGC (Solar Heat Gain Coefficient)**: Must comply with the values provided in Table J4D5, which ensures the roof light manages solar radiation effectively, minimizing cooling loads.
* **Total System U-Value**: Must not exceed U3.9, ensuring that the roof light offers adequate insulation to reduce heat transfer and improve overall energy efficiency.

#### Table J4D5 Roof lights – Total system SHGC

| Roof light shaft index | Total area of roof lights up to 3.5% of the floor area of the room or space | Total area of roof lights more than 3.5% and up to 5% of the floor area of the room or space |
| ---------------------- | --------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------- |
| <1.0                   | ≤ 0.45                                                                      | ≤ 0.29                                                                                       |
| ≥ 1.0 to < 2.5         | ≤ 0.51                                                                      | ≤ 0.33                                                                                       |
| ≥ 2.5                  | ≤ 0.76                                                                      | ≤ 0.49                                                                                       |

*The roof light shaft index is calculated by dividing the distance between the roof and ceiling shaft centers by the average internal dimension of the shaft opening at the ceiling (or diameter for circular shafts).*

*The area of a roof light refers to the roof opening's area through which light enters the building.*

*The total area of roof lights is the sum of the areas of all roof lights serving a particular room or space.*

## J4D5 Roof Lights on Better Building

Speckel automatically checks the provisions of J4D5 Roof Lights against your design, assessing the total floor area of the room or space below a roof light or skylight and the performance of transparent and translucent elements stipulated in Table J4D5.


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