A quick look at the factors that need to be considered when designing a domestic or ‘private’ staircase, ensuring it will conform to the Building Regulations and be ‘safe for persons moving between different levels in or about the building’.
Illustration care of Chudley 11th Edition Building Construction Handbook
- Maximum pitch – the maximum pitch for a stair is 42 degrees measured along the string line. Shallower pitches can be used but they will take up more floor space and need more trimming at first floor to maintain head height.
- Minimum width – There is actually no minimum width for an internal private stair. Standard design uses a 860mm width but this is simply for practicality for things like trying to navigate a wardrobe or double bed up and around landings. There is a dimension of 900mm to flights of steps to the principal entrance where an external ramp cannot be provided due to a severely sloping site.
- Landing space – A landing is required at the top and bottom of flights equal to at least the width of the stair (width and length). At the foot of the stair this can be reduced to at least 400mm clear of any door swing across the bottom landing. This relaxation is because a person at the bottom of the stair is unlikely to be severely injured by a fall whereas the consequence of falling from the top landing are much more severe. Cupboards on a half landing can open onto the stair as long as at least 400mm remains clear with the doors open.
- Height above stair – 2m is the minimum height required when measured vertically at the pitch line (the front of each step). This can be reduced to 1.9m measured at the centre of the stair for loft conversions where 2m cannot be achieved. This is over the stair and landing.
- Height of guarding – there must be guarding 900mm high to the stair, landings and edges of internal floors to avoid falling through or over the guarding. The guarding should not be easily climbable so you usually use vertical balusters.
- Rise and going – the rise (height) and going (tread) of steps must be consistent throughout the flight. For private stairs the maximum rise is 220mm and the maximum going 300mm. There is also a minimum rise of 150mm and a minimum going of 220mm. You couldn’t use the maximum rise and minimum going as this would give a pitch of 45 degrees and exceed the maximum 42 degrees. The normal relationship between the dimensions of rise and going is that twice the rise plus the going (2R+G) should be between 550 and 700mm. So for a 2.6m floor to floor height a flight one solution would be 13 rises at 200mm plus any going between 220mm and 300mm (2x200[R] + 300 [G] = 700mm). If only 12 rises of 217mm were used (see 12) then the going would have to be between 220mm and 266mm (2x217 [R] + 266 [G] = 700mm). Remember though that the tread of the going will be longer if the tread overlaps the step below.
- 600mm and above – Guarding needs to be provided for any stair where there is a drop of more than 600mm.
- 100mm maximum openings – Any openings to stairs within guardings or open risers must be constructed so that a 100mm diameter sphere cannot pass through. This is to prevent a choking hazard for small children. If open risers are used then the stair treads must overlap by a minimum of 16mm.
- 50mm minimum tread – when tapered treads or winders are used instead of a quarter landing on stairs less than 1m wide, there should be at least 50mm minimum tread at the narrow end and the going should be equal to the straight flight when measured at the curved centreline.
- Continuous handrail – There should be a continuous handrail throughout the flight positioned between 900mm and 1000mm from the pitch line. The handrail can be the top of the guarding if heights can be matched. If the stair is wider than 1000mm then a handrail is needed on both sides.
- Alternating tread to lofts – Alternating tread stairs and fixed ladders with handrails on both sides can only be used for loft conversions to create a single room and only when there is insufficient spaced to fit a standard stair. It must be in a straight flight or flights and diagram 1.10 in Approved Document K gives more detail (see below). Even with space constraints and customer demands its worth considering that both of these solutions can be difficult to navigate, both hands are needed and ascent and descent needs to be facing the stair /ladder.
- We didn’t really have a twelfth step but thought it apt to stop here as there is a maximum of 12 risers in a flight required for a general access stair such as common stairs found in apartment buildings :o)