Energy Efficiency in Historic Buildings
Insulating dormer windows
This guidance note provides advice on the principles, risks, materials and methods for insulating dormer windows. Dormers come in a large variety of shapes, sizes and materials and can be a difficult area to insulate, but if insulation is left out or is poorly detailed then the energy efficiency of the whole roof can be compromised.
Dormer windows are often a very prominent feature of many historic buildings and come in a large variety of shapes and sizes and materials. They can be a difficult area to insulate but, if insulation is left out or is poorly detailed then the energy efficiency of the whole roof can be compromised.
Retro-fitting insulation to any existing building is not straightforward. Considerable ingenuity and attention to detail is required to ensure that the insulation is installed effectively at every awkward junction and gap. Solutions will normally need to be individually designed for each situation and professional advice will often be required.
A change in the proportion and external detailing of dormer windows is rarely satisfactory. This is particularly important if their design reflects that of other windows below or of dormer windows in neighbouring buildings. The insulation of dormer windows should therefore be discussed in advance with the local authority conservation officer.
The upgrading of dormer windows should wherever possible be undertaken in conjunction with general roof upgrading work.
The main aims when insulating a roof with dormers should be:
- To upgrade the thermal performance of the dormer window as much as possible
- To add enough insulation to the dormer to prevent heat loss and cold bridging
- To ensure that air-tightness is maintained around the dormer, preventing draughts
- To ensure that ventilation paths to any ventilated roof spaces above the dormers are not disturbed
- To minimise the risk of corrosion to the underside of any lead used to clad dormer cheeks or roof by careful detailing and installation
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