Dormer skylight: what is it and why

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Dormer windows are almost an integral attribute of many buildings of the last century with pitched roofs. The purpose of this element is not clear to everyone, so today we will deal with the purpose, functions and the need for the construction of such windows in a private house.

Dormer skylight: what is it and why

What is a dormer window

The very phrase “dormer” can be misleading, because it is not intended to listen to anything. The fact is that earlier the word “hearing” was given an alternative meaning: opening, air, that is, in fact, meant a hole.

Dormer windows are installed in pitched roofs and are of several types. The most popular are windows protruding from the slope to form a triangular pediment. Some modifications are supplemented with straight walls at the base, while the frontal part acquires the “house” profile. Depending on the architecture of the building and the configuration of the roof, dormer windows can have an arched ceiling, be covered with one longitudinal slope and even have panoramic glazing – in a word, they can take any shape necessary for the unity of the architectural style.

Dormer skylight: what is it and why

Skylights can also be considered dormers, but they have a slightly different purpose and structure. The main structural difference lies in the framing of the window with a sealing contour and special strips, while between the roofing of the dormer window and the slope, standard methods of making roof junctions – ridge and valley – are used. On the other hand, the roof window provides full illumination, it also has high energy-saving requirements, which is often not important for a conventional roof window..

Purpose and functions

But what is a dormer window for then? To answer this question, you should consider the thermal engineering model of the roof and attic floor in summer and winter.

Dormer skylight: what is it and why

In the cold season, when the building is heated from the inside, a certain amount of heat and water vapor penetrates through the ceiling. The attic, operated in cold mode, acts as a sealed airlock, eliminating the effect of wind on the thermal protection circuit and slightly raising the outside temperature.

However, the ingress of steam into an enclosed space does not pass without leaving a trace: moisture freezes on the supporting structure and the seamy side of the roof because it has no opportunity to escape into the external environment. Thanks to the dormer windows, moderate air exchange with the outside without intensive flows is maintained in the attic, so the overall thermal regime of the roof does not change too much, but the formation of frost does not occur.

Dormer skylight: what is it and why

In summer, the dormer window contributes to active ventilation of the under-roof space and cooling of the attic floor. This effect may seem insignificant, but history knows many examples where dormers have been incredibly useful. One of these is the re-equipment of the roof of the Moscow Manezh, where the damage to the ceiling of the upper floor from overheating was eliminated by inserting dormer windows. It is believed that the name of the windows came from the name of the master, who led the team of roofers involved in this project..

Dormer skylight: what is it and why

It should be noted that the presence of dormer windows allows you to equip a warm attic, which remains airtight in winter and ventilated in summer. In addition, enough light enters the attic through the skylights to inspect the ceiling and rafter system. Also, through the dormers, there is access to the roof surface.

Features of the device

When installing a skylight in the roof, three important nuances must be taken into account: the height of the inset, the connection with the rafter system and the abutment of the roof covering. With the height of the inset, everything is simple: in the Mauerlag area there is an irrationally used volume of the under-roof space, therefore, in most cases, it is advantageous that the bottom of the opening is located at the level of the attic floor. However, if the roof has a long eaves overhang or the rafter system is on the parapet, the window will inevitably crash at some height.

Dormer skylight: what is it and why

The width of the dormer is limited by the distance between the rafters. The inset of the window in the section of the slope, which is crossed by the rafter leg, inevitably necessitates the strengthening of the supporting system, the installation of additional struts and struts. Of course, there are roofs with a frequent pitch of rafters and in such cases, the completion of the rafter system is inevitable, however, it is preferable to mount several small windows rather than one large one.

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