Where possible a conventional stair should be installed to the new storey. Other alternatives are allowable in certain circumstances, such as a fixed ladder or a space saver stair (see below).
Steepness of the stair
- The rise of the new stair should be no more than 220mm, and the going (tread less nosing) no less than 220mm. The pitch should be no steeper than 42°, so the minimum going cannot be used with the maximum rise. A good guide is that twice the rise plus the going (2R + G) should be between 550mm and 700mm.
Width of the stair
There are no minimum recommendations for stair widths, but the need for furniture to be moved up and down the stair should be considered.
It is suggested that:
- where there are two new habitable rooms on the new storey, or where a unique facility is provided on this storey (e.g. the only bathroom to a dwelling), the stair should be at least 800mm wide, or
- if there is only one room on the new storey the stair should be not less than 600mm wide.
- The going in the centre should be no less than for the straight flight.
- All the tapered treads should have uniform goings.
- There should be a minimum tread of 50mm at the narrow end.
Headroom over the stair and landings
A clear headroom of at least 2m should be provided over the new stair and landings at the top and bottom, and if the new stair rises above the existing stair or landings, then 2m clear headroom should be maintained (see diagram below).
If 2m clear headroom to the new stair cannot be achieved, then 1.9m to the centre of the stair with a minimum of 1.8m at one edge can be accepted (see diagram below).
Handrails and guarding
- There should be a handrail on at least one side of the stair.
- The handrail should be 900mm above the pitch line.
All landings, stairs and edges of floors with a difference in level of more than 600mm should be guarded.
- The height of the guarding to be at least 900mm,
- There should be no gaps larger than 100mm, and
- They should not be easily climbable by young children (e.g. no horizontal rails).
Altenatives to a conventional stair
- These should be designed in accordance with BS 5395: Part 2.
- Generally to comply with the requirements for rise, going and headroom, the outside diameter will need to be between 1.3m - 1.8m.
Space saver (or alternating tread) stair, or a fixed ladder
When there is not enough space to install a conventional stair (complying with the above requirements) in a loft conversion consisting of one habitable room only, then an alternative (space-saver or fixed ladder) may be considered. For further advice on this, please refer to Building Control.
Going: the distance measured on plan across the tread less any overlap with the next tread above or below.
Headroom: the vertical distance above the pitch line or the surface of the landing.
Nosing: the 'overlap' of one tread to the next.
Pitch: the angle between the pitch line and the horizontal.
Pitch line: a line connecting the nosings of all treads in a flight.
Rise: the vertical distance between the top surfaces of two consecutive treads.