Choosing the correct dormer or rooflight for a listed property
When converting an attic or adding an extension to a Listed property, a key issue is the provision of natural light and ventilation. In order to secure Listed Building Consent, an appropriate arrangement of dormers and/or rooflights will be required. What is appropriate depends very much on what type of roof is proposed – its size, angle, height and the type of roof tiles used.
Many people prefer dormers because they contain normal vertical windows which one can stand in front of to see out. However there is a limit to the number of dormer windows a roof elevation can accept, and there are many situations where use of a dormer is not appropriate, either because there is not enough space for it, or because the disposition of the roofs or windows below would make it look awkward or ‘out of focus’.
Whereas dormer windows are regarded as architecture with a capital ‘A’ – i.e. they are seen as significant architectural elements, rooflights take a subsidiary role in the architecture of a building and are therefore a less conspicuous way of providing light and ventilation. Moreover rooflights are considerably less costly than dormers, and they provide more light – about 20% more than the equivalent sized vertical window – on account of the fact that they point upwards towards the sky.
Generally speaking windows look better when they get slightly smaller on their way up an elevation. This is not always the case, but it is a good rule of thumb to follow. So the windows framed by dormers should ideally be a little smaller than the windows of the floor below if visual harmony is primary. The shape and style of the dormers should closely follow local architecture; neighboring properties will provide a good pointer for the overall design.
As to rooflights, these need to be sensitively detailed if they are not to detract from the roof of a historic building. Generally speaking the look of original cast iron Victorian rooflights is preferred, as these lie more or less flush to the adjoining roof tiles, whereas many modern roof windows stand somewhat proud of the roof and are chunky in appearance.
In a survey carried out with Conservation Officers, flushness was the most important characteristic cited for rooflight design. The second most important feature was size; don’t be tempted to install a larger size than you require, particularly if it is a front elevation as this is considered more sensitive by Planning Departments compared to the rear elevation. Further characteristics of this type of rooflight include relatively fine glazing bars and the glazing is generally split into long narrow sections.
Smaller historic property was often extended in an ad-hoc and organic manner. So whatever means of admitting light and ventilation is chosen for new additions or loft conversions – dormers or rooflights – it is important to recognise and keep to the spirit of the original building. If the original was quite a formal building then perhaps dormers lined-up with windows below might be more appropriate. Where the original building is informal, either a mix of dormers and rooflights or rooflights of different sizes would be more in keeping with the original architecture.
When converting barns or stables, dormers are simply not appropriate as they would never have appeared on agricultural buildings of this nature. Rooflights can work very well, but there are two rules to ensuring appropriate intervention. Firstly the rooflights should be set out in a random way – not in a row and secondly there should be variation in size. As barns are part of our vernacular architecture, a formal or ‘tidy’ approach may look out of place.
In all cases it is best to consult your local Conservation Officer at the earliest stage in the design process. This will save time and money.
Summary of tips
- Ensure you have a ‘conservation rooflight’ of an appropriate size as modern rooflights do not have the correct features
- Dormers should generally be smaller the further up the building they are placed
- Dormer windows are usually inappropriate for barns and stables
- Rooflights on barns and stables should be set out in a random way
- Contact you local Conservation Officer to save time and money