Dormer windows - shapes and facts

Unlike a simple skylight, a dormer not only brings a lot of light into the loft. It also creates more living space, as it opens the roof upwards and the sloping roof in the dormer area is omitted.

Types of dormers

Over the centuries, the dormers have always been subject to fashion and various architectural styles. So there are now many forms and types of dormers. There are also many hybrids commonly used in which two or more dormer forms merge together.

Similarly, the demarcation to the Zwerchhaus, which already begins directly at the ridge, is often no longer so clear today. In terms of structural engineering, this often occurs in the dormers. Only the bay window is still clearly different from a comparable dormer.

Dormer windows - shapes and facts: shapes

Here we have put together the most common basic forms today with their special advantages and disadvantages to provide an informative overview.

shed dormer

The Schleppgaube is not without reason the first mentioned dormer. It is most often used in this country. There are different characteristics. The closer the tow dome approaches the ridge, the greater the space gain achieved by this dormer shape.

However, the high approach of the dormer also has disadvantages that are noticeable in terms of cost. Since the roof surface is opened further, the rafters must be replaced with other static elements.

These changes in the roof truss require a lot of knowledge from the roofer and cause a lot of work that can not be avoided on the roof during the transformation. However, these costs finally pay off again through the gain in living space.

gabled dormer

The gable dormer often looks more like a small bay window. In contrast, the gable dorm still has a piece of the roof area at its feet, while the bay window usually reaches down to the ground.

Thanks to the small gable in this dormer shape, it is possible to direct a lot of light into the rooms under the roof. Today, the entire dormer gable is usually glazed.

The gable gable makes high demands on the care of the roofer. Most are on both sides both a disguise and a separate eaves necessary. In addition, the gable dormer must be integrated into the existing roof and the transitions must be well sealed.

bat dormer

The dormer offers the highest degree of difficulty of all dormer forms with a very low gain in light or space. Nevertheless, this dorm has always found its lovers and fits in very well with a villa style.

The curved form of the bat dorm rises like the eponymous wings of the bat already far from the actual dormer away from the roof. This brings the high cost of this dormer shape with it, but also contributes to their elegance.


Similar to the hipped roof, the hive has a gently sloping roof in all three directions that protrude from the roof. The dormer also has a small own ridge, from which the roof sides go off.

Optically, the canopy naturally adapts best to a hipped roof or a crippled hipped roof, although it is conceivable on almost every roof shape. It is very robust and dissipates the wind well.

Spitzgaube or triangular dormer

The dormer is often more of a style element and does not offer much space. The light output is rather low in the triangular dormer. From a small own ridge, the two roof sides of the dormer are pulled down obliquely to the actual roof.

The ratio of the cost to the gain in space is rather bad for the Spitzgaube.

Round dormer or barrel dormer

The round dormer or barrel dorm rises either with straight sides and a curved roof part from the roof surface or protrudes directly as a semicircular element. This form is very modern and usually offers a lot of space.

However, the semi-circular construction of the roof surface is very expensive and the roofer requires much working time on the roof, if the dormer is not placed directly as prefabricated component.

Dormer - glazed all around

The dome looks almost like a small greenhouse, which protrudes from a roof. In addition to the advantage of gaining space, the dormer provides an enormous light output, even if it may be mounted on the north side of the house.

Light and shadow

In a dormer there is no way to damm the roof of the dormer. Therefore not only a lot of light gets into the room under the roof, but also the cold can penetrate more easily. Likewise, it is usually necessary to ensure sufficient shading in the summer months.

These disadvantages add up together with the rather high cost of the fully glazed dormer. Therefore, this dormer shape is very often used only on architect houses or other modern architectural styles.

prefabricated dormers

Many dormer forms are available today as prefabricated dormers. These are prefabricated, similar to a prefabricated house in a factory hall. The complete dormer is placed on the open roof with a crane. Later, only the roof needs to be adapted to the new part of the building.

Prefabricated dormers can indeed be made much cheaper than a traditionally built dormer. However, the roof must be accessible by crane. However, this is no longer the case in many residential areas today.

Typical problems with dormers

An overview of the typical problems that can occur when building dormers.

  • Seal towards the roof area
  • Statics problems due to removed rafters
  • Insulation often inadequate


The seal between dormer and roof surface is often a problem if it is not carried out carefully. Especially in difficult constructions inexperienced roofers have difficulties to make the connections clean.


If rafters are removed and possibly also a Mittelpfette, then for these static elements a balance must be created. This is often performed only insufficiently. If in doubt, you should plan the extra cost for a proper structural engineer in large dormers.


The insulation in a dormer construction can be a problem if the connections are not worked properly. Especially the dormer is exposed to increased wind forces. So if the corners and transitions are not carefully overlapped, the wind can whistle through the entire dormer.

Tips & Tricks

If you think about a dormer window, look at beautiful examples on comparable houses. To ensure that your dinghy is a success, and not later a disaster in terms of insulation and waterproofing, you only hire absolutely experienced roofers or even consult an architect or structural engineer. You must also consider the need for a building permit for this building change, so that your dormer do not have to tear down right after completion.

Video Board: 7 Architecture Facts pt.26 | Lloyds, Brasilia, Niemeyer & Facade