How to choose dormer windows and what is important when fitting them

Roof windows, often called "veluxuri" on the same pattern that we say sneakers sneakers and children's xeroxes of various documents, arose out of the need for extra light. Before them, attics were illuminated by dormer windows, additional constructions that allowed the window to be fitted straight up. However, the amount of light was greatly reduced by the small tunnel formed by the skylight, and ventilation was difficult. The special construction of the windows mounted directly on the roof allowed light to enter directly, while preventing water and wind from penetrating. Attics are now unthinkable without these windows, and their performance is getting better and better. To achieve this performance, however, it is important that the choice and installation are correct.

Windows providing ventilation and light. Attic window manufacturers

As early as the end of the 19th century there were attempts, some of which were patented, to make roof windows that would bring as much light inside as possible, keep out water, be easy to install and operate. The first patent for a system for rotating a wooden window was registered in the UK in 1894. This was followed by a series of patents, registered in countries in Europe and the USA, which simplified closing and opening, increased watertightness and wind resistance. The name roof window was first used in 1931 in Germany.

Velux is the name given by Danish engineer Villum Kann Rasmussen to the first roof window built and patented in 1942. The window was designed to illuminate attic spaces in schools that had been converted into classrooms. It was the solution to increase the number of pupils learning in the shrinking wartime spaces. Rasmussen wanted to make a better roof window than a vertical one to fill the attic spaces with light and fresh air.

The window was "baptized" Velux, a combination of ventilation and Lux (Latin for light). The window was the first of its kind mass-produced by Rasmussen's company. Now the VELUX Group is the world's largest manufacturer of windows and roof lighting systems. Its main competitors are the Polish company FAKRO and Germany's ROTO. There are other roof window manufacturers, but their market share is very small. Deposib has in Sibiu one of the largest showrooms in the country for such windows.

What's important when deciding to install roof windows

Unlike ordinary windowsThe roof tents, which can be made to order, have fixed dimensions. They are chosen according to light requirements, roof structure and rafter placement. In order to have a sufficient amount of light, the recommendation is that the glazed area should be at least 10% of the floor area.

In new houses, the window is not fitted as soon as the roof has been framed. Wood used in construction It will continue to dry out and decrease in size. If the window is fitted immediately, the re-shrinkage of the wood will affect the tightness of the fitting and seepage will occur. The recommendation is that windows should be fitted 3-4 weeks after the sash is installed.

If the window is to be fitted to an old house, it must first be seen whether the structure of the house allows it. The recommendation is to consult a building engineer. For fitting, the roof must be stripped in the area where the window is positioned. After fitting, the sheathing must be replaced and the covering frame installed to protect the window by guiding water outwards.

The width of the window is chosen according to the distance between the rafters and should be 4-6 cm less. Windows larger than this distance can also be fitted as there are ways of altering it without affecting the strength of the building. The length of the window depends on the pitch of the roof. To get enough light, longer windows are fitted on low-sloped roofs. Shorter windows can also be fitted if the roof slope is steep.

The rain tightness of windows is tested according to EN 1027/12208. Depending on the test results there are several quality classes. Wind resistance is tested according to EN 12211/12210 and shock resistance according to EN 13049.

Types of roof windows

Depending on how they open, roof windows come in many different types. Here are some of them:

• Double-hinged windows - the catch is at the top and opens outwards. Recommended in rooms where you can look out of the window as they provide unobstructed views.
• Mid-hinged windows - pivot opening with the axis of rotation in the middle of the sash. Most commonly used due to ease of handling. Can be fitted anywhere.
• Supramedian hinged windows - pivot opening with the axis of rotation above the middle of the window. Very suitable for tall people.
• balcony windows - casement windows that open to form a small balcony. Suitable for attics high enough to allow normal use of the small balcony formed.
• bottom-hinged windows - the catch is at the bottom. For spaces requiring very good ventilation. Allows very good smoke evacuation.
• Side-hinged windows - opening at the side. Recommended for easy access to the roof.

Each of these types have different sizes, finishes, frame materials. The glazing has between 2 and 4 layers, providing different levels of energy efficiency. They can be fitted with sensors that automatically close them when the air humidity rises, opening and closing can be operated remotely by remote control or telephone.

Attic windows for passive house

Demands for energy efficiency in buildings has automatically led to special requirements for roof windows. Manufacturers adapted quickly, with some already producing windows certified for passive houses. This certificate simplifies the process of obtaining a Passive House certificate, eliminating the need for an audit for windows.

In order to reach the required parameters to be certified as passive manufacturers use different methods: they use 4 layers of single glass or 3 layers of laminated glass (multi-layered). In the space between the layers they put argon or krypton. The frame has inner chambers for insulation, is thicker or is made by combining different materials. High-performance sealing gaskets are used. This results in a heat transfer coefficient of the window below 0.6 W/m²K. Correct installation with foils and sealing strips can lower the value even further.

I hope you find the information useful. As always, additions are welcome. And if you have any questions or queries, please leave them below in the dedicated space. I will be sure to reply.