Why does VELUX recommend 20% glazing?

For roof windows it can be generally said that 15% glazing to floor area usually puts you on the safe side of meeting the European Standard EN 17037 median daylight requirements.

Our rule of thumbs is therefore to have from 15% to 25% in order to reach good to very good daylight in your room. The simplified calculation of this ratio proposed on this website takes into account the full window size, including the frame, therefore our recommendation increase by 5%, to compensate for the frame area, ending up to 20%.

When should you consider more than 20%? If you know the window will be subject to shadow and obstruction, consider to stay on 25%-30% window to floor ratio.

5 things you should know about daylight

1. Did you know that daylight is more powerful from above and that roof windows can provide 2 to 3 times more daylight than façade windows. At the same time it is equally important to be able to regulate the heat. Our awning blinds and exterior shutters can help you with that**.

2. Exposure to daylight is crucial for your health to ensure a good circadian rhythm. Conversely, it is equally important to have complete darkness when you sleep to improve your quality of sleep. Our blackout blinds and can help you with that*.

3. If you want to be more alert, mentally and physically active and perform at your best, you need to expose yourself to plenty of natural daylight*.

4. Daylight can improve your productivity by up to 15% and speed of learning and information retention by up to 18%. Recovery time and pain relief also benefit from more daylight. More daylight will improve both by as much as 21%*.

5. If you have decent daylight you will also save on electric lighting in your home*.

Source:
*https://www.velux.com/what-we-do/research-and-knowledge/deic-basic-book/daylight/benefits-of-daylight
**https://www.velux.com/what-we-do/research-and-knowledge/deic-basic-book/daylight/daylight-with-roof-windows-flat-roof-windows-and-modular-skylights

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