ABOVE: The perfect dormer — just under halfway up the roof, and small enough not to dominate the elevation.

A dormer is a vertical window with a roof of its own, positioned, at least in part, within the slope of the roof. When dormers are ‘correct’ they can look wonderful. When things go wrong they look ghastly. It is a question of both size and position.

Many self-builders forget that when early cottages were built there were no dormers — because there were no window openings at first floor level. So vast numbers of cottage dormers are actually retrofits — and yet so often they appear original. Why? Because they are not too big, and they are in proportion with the roof, which is both large and steeply pitched.

Translate this to a modern one-and-a-half storey house – many self-builders end up with them because they cannot gain permission for two storeys – and the lesson is always the same: keep the dormer windows in proportion. If you look at any number of spec-built ‘dormer bungalows’, the most unsatisfying visual feature is usually that the roof windows are too big, meaning that the front elevation is out of proportion.

The roof of the dormer should be in keeping with the style of the roof itself

ABOVE: The roof of the dormer itself should at least refer to the style of the main roof, as in this case; BELOW: An eyebrow dormer – named for obvious reasons – makes for a charming design feature. The dormer windows in this picture are part of a bungalow built by serial self builder Len Dean

An eyebrow dormer can make for a very interesting design feature

“If you give the house a big roof – even if it is only one-and-a-half storeys – then relatively big dormers may look alright,” says specialist Arts & Crafts architect Peter King (cardenking.co.uk). “However, a big roof might be the very thing you are trying to avoid because of planning constraints.”

One of the key things to avoid, Peter stresses, is ‘stick-on features’ — features that are added with a total lack of design confidence. For loft conversions, dormers must be an integral part of the overall design, rather than simply the largest roof windows you can get away with. If they appear ‘boxy’ and over-large the result will be terrible because they will overpower the rest of the house. An additional danger nowadays is the desire of many builders to over-insulate. In fact, modern high performance insulation can quite easily be packed into the cheeks of a dormer without unduly increasing the thickness.

With a large late-Victorian or Edwardian house containing a loft conversion, inserting roof dormers can actually enhance the elevation (especially in an urban situation) by adding to the verticality and reducing the ‘squatness’.

With younger houses, however, the reverse can often be the case. The classic is the dormer in the roof at the front of a semi-detached pair. Here a dormer on one side – assuming you can get planning permission – may well create a look of imbalance, and be a visual disaster.

Dormer windows should fit well with the overall house design

ABOVE TOP: It seems the grander the house, the smaller and spindlier the dormers — to great success; ABOVE LEFT: a flat-roof dormer can look perfectly in place, as on this new Arts & Crafts-style house; ABOVE RIGHT: A more traditional dormer, which would have perhaps benefitted from being positioned just below the ridge line.

One way in which dormers in these sort of houses can succeed is to build straight up from the outside wall to form a new glazed gable end, which is, in effect, the dormer. A flat projecting lead roof can complete the look quite successfully. However, to achieve a really good effect, both houses would have to be treated in the same way.

In many ways, the ‘easiest’ place in which to position a dormer – that is, the situation in which you are least likely to get it wrong – is in a traditional cottage. Whatever the style of house, however, dormers inevitably look better if their ridges are kept well down from the main ridge. It is best to place them slightly lower than halfway down the roof. If they threaten to get close to the ridge, then the usual practice is to flatten their roofs.

Another key to a successful dormer is the roof pitch. There is no harm in having the pitch of the dormer steeper than that of the main roof, but if they are kept the same it will usually be possible to have tiled – as opposed to lead – valleys.

It is also wise to allow the roof of the dormer to follow the style of the main roof: i.e. hips with hips and gables with gables. A dormer placed in a hipped gable should also have a hip, otherwise it will look very odd. With a shallow roof pitch, often clad with slates, a flat-roofed dormer will look much better than one with a pitched roof.

Above all, try to put in a great deal of effort at the design stage. Play around with the elevations until they look ‘right’. Then choose materials very carefully, so they do not make the dormer too bulky. As Peter King says: “Remember, dormers are one of those features in which delicate nuances and fine judgements matter. And biggest is definitely not always the wisest.”

What to avoid

Dormers need to be an integral part of the overall house design and generally subservient to, or at least picking up the design guidelines of, the existing roof shape. The tendency to go too large (BELOW), particularly on smaller homes, is what leads to common mistakes.

Dormer windows should look like part of the house, rather than an addition

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