WORTH KNOWING
What is energy saving skylights?
Primalux Skylights have Low U-Values (1.8 W/m2K or less), Making Them Very Energy Efficient
The Danish building regulations (BR08) require a maximum U-value of 1.8 W/m2K for skylights on roofs in heated buildings. BR95 permits the installation of skylights with a maximum U-value of 2.0 W/m2K, making allowance for the increased heat loss in other places of the building.
An indication of how standards have improved over the years is the fact that many old skylights installed on roofs in Denmark have a U-value of approx. 4.9 W/m2K.
BU-Values And Heat Loss
Below we have used diagrams to illustrate how great an influence skylight U-values have on a building’s total heat loss. The diagrams show how much heating oil and insulation are needed to compensate for the heat loss of the skylights. The basis of the values in all diagrams on this page is a concrete roof of 1000 m2 with 50 m2 skylights.
The skylights have a total transmission area of 125 m2. The insulation used has two layers, where the upper 50 mm has a λ-value of 0.040 W/mK and the underlying insulation a λ-value of 0.038 W/mK
The Danish building regulations (BR08) require a maximum U-value of 1.8 W/m2K for skylights on roofs in heated buildings. BR95 permits the installation of skylights with a maximum U-value of 2.0 W/m2K, making allowance for the increased heat loss in other places of the building.
An indication of how standards have improved over the years is the fact that many old skylights installed on roofs in Denmark have a U-value of approx. 4.9 W/m2K.
BU-Values And Heat Loss
Below we have used diagrams to illustrate how great an influence skylight U-values have on a building’s total heat loss. The diagrams show how much heating oil and insulation are needed to compensate for the heat loss of the skylights. The basis of the values in all diagrams on this page is a concrete roof of 1000 m2 with 50 m2 skylights.
The skylights have a total transmission area of 125 m2. The insulation used has two layers, where the upper 50 mm has a λ-value of 0.040 W/mK and the underlying insulation a λ-value of 0.038 W/mK
Fuel Consumption And U-Values
Diagram 1:
Shows how much heating oil is needed annually in order to compensate for the heat loss from the skylights in proportion to the U-value.
Diagram 1:
Shows how much heating oil is needed annually in order to compensate for the heat loss from the skylights in proportion to the U-value.
How Primalux Skylights Reduce Fuel Consumption
Diagram 2:
Shows how much heating oil you can save annually by installing a Primalux energy saving skylight, in proportion to the oil consumption. The skylights have a U-value of 1.8, which is the requirement of the Danish building regulations (BR95).
Diagram 2:
Shows how much heating oil you can save annually by installing a Primalux energy saving skylight, in proportion to the oil consumption. The skylights have a U-value of 1.8, which is the requirement of the Danish building regulations (BR95).
How Poor U-Value Skylights Increase Your Need For Roof Insulation
Diagram 3:
Shows how much additional insulation has to be placed on the roof in order to compensate for the bad U-value of the skylight. Please note that it is not possible to compensate by increasing insulation for U-values above 3.4
Diagram 3:
Shows how much additional insulation has to be placed on the roof in order to compensate for the bad U-value of the skylight. Please note that it is not possible to compensate by increasing insulation for U-values above 3.4
Diagram 4:
Shows Diagram 3 for U-values from 0.5 to 3.1 in detail. Shows both the total insulation quantity in connection with the individual U-values and savings and additional consumption respectively.
Shows Diagram 3 for U-values from 0.5 to 3.1 in detail. Shows both the total insulation quantity in connection with the individual U-values and savings and additional consumption respectively.
Table with U-values for skylights and the belonging saved, additional and total insulation thickness on the roof.
| PRIMALUX SKYLIGHTS | ||
| U-value of the skylight | Insulation in rooF | |
| SAVED | Total | |
| 0,5 | 78 | 91 |
| 0,6 | 74 | 95 |
| 0,7 | 71 | 98 |
| 0,8 | 67 | 102 |
| 0,9 | 62 | 107 |
| 1,0 | 58 | 111 |
| 1,1 | 53 | 116 |
| 1,2 | 47 | 122 |
| 1,3 | 41 | 128 |
| 1,4 | 35 | 135 |
| 1,5 | 27 | 142 |
| 1,6 | 19 | 150 |
| 1,7 | 10 | 159 |
| STANDARD SKYLIGHTS | ||
| U-value of the skylight | Insulation in rooF | |
| Additional | Total | |
| 1,8 | 0 | 169 |
| 1,9 | 12 | 181 |
| 2,0 | 25 | 194 |
| 2,1 | 41 | 210 |
| 2,2 | 57 | 226 |
| 2,3 | 79 | 248 |
| 2,4 | 102 | 271 |
| 2,5 | 135 | 304 |
| 2,6 | 169 | 338 |
| 2,7 | 222 | 391 |
| 2,8 | 277 | 446 |
| 2,9 | 362 | 531 |
| OLD SKYLIGHTS | ||
| U-value of the skylight | Insulation in rooF | |
| Additional | Total | |
| 3,0 | 486 | 655 |
| 3,1 | 683 | 852 |
| 3,2 | 1050 | 1219 |
| 3,3 | 1962 | 2131 |
| 3,4 | 7997 | 8166 |
| In connection with values higher than 3.4 it is no longer possible to compensate with increased insulation! | ||
Please notice that it is not permitted to insulate the roof worse than a U-value of 0.25 W/m²K, which menas in practice you cannot have an insulation thichness below 140 mm in connection with a roof as in our example.
