Draughts
If you experience a draught from your VELUX roof windows, this may be for various reasons:
Changing the gaskets
The gaskets in a VELUX roof window are developed for airtightness, but if your gaskets are old (more than 10 years old), they will probably be stiff and dry and no longer capable of providing the required airtightness. Therefore, cold air from the outside will penetrate the gaskets and result in a draught. You should replace the gaskets so that the window can close completely between the frame and the sash. The gasket at the back of the ventilation flap should also seal completely at the ventilation gap.
Fixing of square installation
If your gaskets are okay and you still experience problems with incoming air - especially when it is cold outside - it may be due to the fact the frame and sash are not placed correctly in relation to each other. A square installation may result in the sash not being absolutely parallel to the frame.
Replacement of insulating glass unit
What is experienced as draught is not necessarily an indication the window is not tight at the gaskets. If your gaskets are okay and the window installation is correct, with the frame and sash parallel to each other, what you experience as draught may actually be down-draught from the window pane. An old, ordinary insulating glass unit has considerably lower insulating capability than a new, modern low-energy pane. This results in the cold going through the pane when it becomes cold outside. The air close to the cold pane will also be cooled. As cold air is heavier than warm air, the cold air will fall down (down-draught) and spread over the floor level. You will experience the down-draught as draught from the window, even though it is completely tight. To solve this problem you should replace the poor insulating glass unit with a modern low energy pane. A low energy pane - apart from providing better comfort - will also result in lower heating costs and a better indoor climate by keeping the warmth inside during the winter and outside during the summer.
Re-insulation of lining
Finally, draught may come from insufficient insulation around the window and of the area around the window (the lining). Try e.g. to place a hand on the side of the lining and feel if this is colder than the inner wall. If it is, draught will come in the form of down-draught from this area. The lining should be dismounted and re-insulated. At the same time, the area around the frame should also be checked if it is correctly insulated. Contact your local carpenter to remedy the problem.