When assessing the potential of your loft for conversion, measure the space where there is a clear headroom of 2.0-2.1m or more between the joists and rafters. Once the floor has been built up and the roof insulated, this will leave you with around 1.9-2.0m of headroom, which is the minimum practical ceiling height.
Even if your loft does not currently offer enough space to make it viable for conversion – either because of the roof shape or height, the roof truss design or the position of cold water header tanks – there is probably a design solution that could make it possible. For example, increasing the volume of the roof can make a dramatic difference to the amount of usable space available.
Conversions are defined into different categories according to design and how any potential new space is added:
The existing roof space is converted with no increase to the volume other than the simple addition of rooflights to the front and back. Windows may also be added into the gable walls. This is the most cost-effective option as it involves minimal alteration, but rarely done as does not maximize your potential space.
Full Width Rear Dormer Conversion
A rear dormer extension is the process by which the back slope of the roof is removed and then built up into a box shape from the rear elevation. Rear dormers are usually built off the back wall and up off both the sides, forming a large area with full headroom.
When a roof slopes down to the eaves on all four sides it is known as a ‘hipped’ roof. To increase the usable space within a hipped roof, one (typically on a semi) or more hips can be replaced by a gable wall and the roof extended over the gables to create more volume.
An L-shaped dormer is very similar to a rear dormer conversion but with the added benefit of slightly more space. An l-shape dormer can only be carried out on certain properties. Often victorian properties are converted, where the kitchen and bathroom are located at the rear of the property.
Common in terraced houses, the gable walls are built up and the roof at the back rebuilt to increase the pitch so it is nearly vertical up to ceiling height, effectively forming a wall with windows, and then almost flat back to the ridge, forming a large area with full headroom.
Named after the 17th-century French Architect Francois Mansard, is situated to the rear of the property. This type of conversion has a flat roof, with the back wall sloping inwards at an angle of 72 degrees. Usually has small dormers pertruding the slope at 90 degrees to house windows.
Replacing the Roof
Where there is currently a very shallow pitched roof with little or no usable space, it may make economic sense to remove the roof and replace it with a new structure that has a steeper pitch and more usable space.
In a Conservation Area alterations to the roof may not be permitted, especially increasing the ridge height. A solution is to add more space by lowering the ceiling in the storey below.