Dormer Window Design

Well proportioned dormer windows

Principles of good dormer window design

The design of dormer windows to roofs either in bungalows or two storey dwellings needs careful consideration. The conflict between gaining additional floor space internally and an acceptable architectural pleasing external appearance must be appreciated if a successful dormer addition is incorporated.

The roof line of a dwelling is one of its most dominant features and it is important that any appendage to the roof does not distract from the appearance of the dwelling. This is particularly true for the front of any dwelling, being the prominent view and seen by passers by. In contrast the rear of dwellings usually is not seen and has a lower grade of finish and appearance. Of course there are exceptions to this, but these exceptions are limited to the upper end of the housing market.

Dormer windows matching detailing

Detailing reflected in the design of the dormer

Locations for dormers

When considering a loft conversion, one of the first questions asked will be to install roof windows or dormer windows. If possible a dormer should be installed to the rear of the dwelling, but this is not always possible. There may be an extension to the rear of the dwelling and the extensions roof prevents the construction of a dormer. But generally this is the preferred location. Flat roof dormers (not acceptable in front locations) can be constructed to the rear.

Where dormer conversions are being undertaken to the front of dwellings then the following design examples will give some of the do’s and don’ts.


The traditional pitched roof dormer is generally not as wide as the flat roof dormer and often includes decorative features that add to the appearance of the building.


Dormers should be built back from the wall of the dwelling, away from the edge of the roof or adjoining building boundary, and below the ridge of the original roof. It is not appropriate to try to create a traditional style dormer window by placing a pitched roof on a wider dormer. This will result in a most unsuitable feature with an unusually shallow roof pitch and will not give the appearance of a traditional dormer. Such a structure would look out of place and would detract from the character and appearance of the dwelling.


Some dwellings designed and built in the late sixties and early seventies had large flat roof dormer windows to the front elevations incorporated within their design. Although, at the time these seemed to be the new modern look for dwellings, thankfully as with most of the early seventies fashions and trends, they were soon superseded with designs that were more appropriate.


The above examples would not be allowed to be built in our towns and cities today. The planning service is imposing more design control over what is being built.


Traditional style dormers stem from the incorporation of vertical windows in extended height walls. These dormers are used where the external walls extend above the floor level. The eaves are usually between three and five feet above floor level. This style is still used in modern dwellings to good effect. The next example shows this style of dormer windows to the main dwelling and a matching dormer within the garage roof.


Dormer finishes

The dormer windows to the front elevation should be finished in the same material as the main dwelling. The sides of the dormer should match the roof covering with slates or tiles hung vertically. Where this is not possible then the sides of the dormer may be covered in cladding materials. The front of the dormer should not be covered in cladding. The use of low maintenance materials should be used to avoid the dormer becoming unsightly through neglect.


Size of dormers

The size, proportion, shape, design, location and finishes of the dormer all contribute to the appearance of the dormer window, each need to be considered if a successful dormer design is to be achieved. Generally dormers over 2.5m wide are too wide, if possible two dormers side by side should be used instead. The converse can also be said to be true, dormers that too small can have odd appearance.



The placing of dormer windows along the roof need to be balanced, a single dormer to one side can make the roof appear off balanced. This can be overcome by matching other featured of the dwelling.


Shape of dormers

Rectangular dormers are not the type of dormers that can be fitted to a roof, Eyebrow dormers have been used for many years and give a pleasing appearance. Eyebrow dormers, because of their shape, require large steeply sloping roofs that have small pantiles covering. Arched dormer windows with a lead roof covering can be fitted to period dwellings. Modern dwelling can be fitted with triangular dormer windows, but care must be taken to balance these with other features of the dwelling.

bad example of dormers to the front of dwelling
Poor example of a dormer window.
sixties dormer windows
Flat roof dormer window
Poor example of flat roof dormer windows to front of dwelling
more sixties dormer windowsSixties style dormer windows to front of dwellings
Flat roof dormer to front of dwelling
Flat roof dormer out of keeping with the rest of the dwelling
oversized dormer windows
Oversized dormers
A sucessful arangement of dormer windows
Good example of splitting dormers to front of dwelling
dormer with gable roofs
Splitting dormers give a more pleasing appearance
dormer window matching tradional dormer window
Dormer window matching traditional dormer window

Undersized dormers give an odd appearance
traditional dormer
Traditional dormer
unbalanced dormer
A single dormer can give the appearance of being off balanced
Dormer matching finishes
Other features can be used to balance a single dormer
balanced dormers
Double dormers give a balanced look
Eyeyebrow dormer
Eyebrow dormer
Arched dormers
Arched dormers
Triangular dormer
Triangular dormer