The ideal location for a staircase to land is in line with the roof ridge: this will make best use of the available height above the staircase. The minimum height requirement above the pitch line is 2m, although this could be reduced to 1.9m in the centre, and 1.8m to the side of a stair. In practice, the actual position will depend upon the layout of the floor below, and where necessary the available height can be achieved using a dormer or adding a rooflight above the staircase or, if appropriate, converting a hip roof end to a gable.
Maximum Number of Steps: The Regulations specify that the maximum number of steps in a straight line is 16. This is not normally a problem, as a typical installation usually only requires 13 steps.
Step Size: The maximum step rise is 220mm, whereas the step depth or ‘going’ is a minimum of 220mm; these measurements are taken from the pitch point. The step normally has a nose that projects 16-20mm in front of the pitch line. However, the ratio of size must not exceed the maximum angle of pitch requirement of 42°. Any winders must have a minimum of 50mm at the narrowest point. The width of steps is unregulated, but in practice the winders are likely to limit the reduction in width.
Balustrading: The height minimum is 900mm above the pitch line, and any spindles must have a separation distance that a 100mm sphere cannot pass through.
Windows & Dormers
The loft conversion will require a means of getting natural light and ventilation, and the most straightforward method is to use rooflights that follow the pitch line of the roof. This type is fitted by removing the tiles and battens in the position that the rooflight will be fitted. The rafters are cut to make way for the rooflight after suitably reinforcing the remaining rafters. The rooflight frame is then fitted within the new opening, and flashings added before making good the surrounding tiling. This type of window is the most economic, and more likely to be allowed without planning permission, under your PD (Permitted Development) rights. Conservation rooflights, which are slightly more flush to the roofline and are made of metal, can also be specified.
Dormers not only give natural light but can add space to a loft conversion; they can be at the ends or sides. They are particularly effective where the pitch angle is high, as the useful floor area can be increased. The mansard type (ABOVE) will give maximum conversion roof space because it projects the maximum available head height, thus giving a greater usable floor area. A hip to gable conversion has a similar effect.
Dormers and other similar conversions are normally installed by opening up the roof, and cutting the required specified timbers to size on site. They normally involve compound angle cuts (SEE BELOW) so may not be a task that a DIYer would like to undertake. Care also needs to be taken with the roof and side coverings, to get a good weatherproof structure.
Some loft conversion companies will make the dormers off site in their workshop and lift into place. This process allows quick installation, and quick weatherproofing.
Dormers can have gabled or hip roofs, and with careful design can enhance a roof line. In practice, a mixture of the available types can result in the maximum light and space, and provide a fire exit.
The plasterboard ceiling in the upper rooms will delay the spread of fire to the roof space in an unconverted house. However, when an opening is introduced for the staircase the risk is shared with the conversion — therefore, safeguards must be in place to reduce the risk.
All habitable rooms in the upper storeys served by a single staircase should have an escape window with an obstructed openable area of at least 0.33m², a minimum 450mm high x 450mm wide, and not more than 1.1m above the floor level. For loft conversions to existing two storey houses, more stringent provisions apply, due to the greater risk associated with escape via high-level windows. These require a new 30- minute fire-resistant floor to the loft conversion, and a protected 30- minute fire-resistant stair enclosure discharging to its own final exit, with fire doors to all rooms (except bathrooms and WC). The fire doors do not need to be self-closing.
At least one mains-operated smoke alarm with battery backup must be installed in the circulation space of each storey. All alarms are to be interconnected.