Dormer Window (or Dormer, Dorma)
A dormer is a gable and vertical window projecting from a sloping roof. Many loft conversions use individual dormer windows for the added space and character they bring to a loft.
Dormers & Dormer Lofts
Dormer windows increase the space at head height in strategic places in a loft.
For example, in an en suite or midway along a bare wall where they break the line of a solid sloping wall and provide a vertical viewing window that also conforms to safety requirements.
Dormer windows are useful additions to loft conversions as they enhance the internal and external character of a property, unlike roof skylights.
Dormer Window Planning
The first stage when planning an attic conversion with dormer loft windows is to have conducted a loft survey. Lofts need sufficient height to be eligible, too low and planning approval will be refused.
Minimum Height Rules
Internal loft height should be a minimum of 1.8 m minimum at the edge of a stair with 1.9 m at the centre line if the ceiling is sloping in order to meet building regulations approval for height.
See page 7 of Approved Document Part K for diagram and explanation. Low lofts can now be developed for habitable use, adding significantly to the functionality and value of your home.
If your loft is below minimum then you may be able to raise the height of the roof or lower the ceilings of lower rooms.
Each dormer is individually constructed to architectural plans and building regulations to ensure the structural integrity of the roof is not compromised.
Dormer windows are constructed by creating a frame within the roof. The dormer sides (cheeks) are built up from the existing roof rafters, even for the gently styled eyebrow dormer.
An initial loft survey is used to assess the condition of roof, roof rafters, building structure and suitable design options.
Building a Dormer Window
Building dormer windows is a staged process, which includes creation of the roof aperture, gable end, installation of windows, cladding and insulation and inside plastering.
- Validate building plans - when working from building plans not produced directly for us we pay particular attention to ensure measurements and angles are accurate before construction begins.
- Roof aperture - support is required if the dormer width spans several rafters. Wood or steel reinforcement is used to bridge rafters and create the dormer frame. Sections of roof rafter can then be safely removed (Trussed lofts require a different technique as removal will damage the integrity of the roof).
- Building the sides. Roof rafters on either side of the aperture provide a base for the dormer frame. Specialist gripping washers secure the bolted series of vertical uprights which become the dormer walls.
- Building the roof. The dormer roof form is specified within the building plans. If the dormer has an angled/pitched roof then rafters are joined at the apex against a ridge board. If building plans stipulate a flat roof then horizontal timbers form the dormer roof.
- Cladding. Cladding provides a waterproof skin to the bare timber frame and prepares the dormer for the roofer to apply felt / laths and tiles.
- Roofing. The completed dormer frame has the roofing material applied:
- roofing felt cladding provides a waterproof skin
- horizontal laths are secured across the dormer rafters
- ridge tiles are secured over the ridge board
- matching tiles are nailed onto and across the laths
- Insulation. Insulation board to maximize heat retention within the loft area is integrated with the dormer timber frame. The insulation conforms to building standards.
- Windows. The dormer window is now fitted. uPVC, wood or hardwood double glazed windows are fitted.
- Plasterboard. Plaster-boarding of internal wall of dormer over frame and insulation boards.
- Plastering and skimming. Double application of plaster to make surface ready for internal wall decorator.