Walls and Window Teatments

WALLS AND WINDOW TREATMENTS 3(1+2)

Lesson 11 : Wall Element – Staircase

Ergonomics And Building Code

Ergonomically and for safety reasons, stairs have to have certain measurements in order for people to comfortably use them. Building codes will typically specify certain measurements so that the stairs are not too steep or narrow. Building codes will specify

1. Minimum tread length, typically 9 inches (229 mm) excluding the nosing for private residences.[3] However, most human feet are longer than 9 inches (230 mm), thus people's feet don't actually fit on the tread of the step.
2. Maximum riser height, typically 8.25 inches (210 mm). Note that by specifying the maximum riser height and minimum tread length, a maximum slope is established. Residential building codes will typically allow for steeper stairs than public building codes.
3. Minimum riser height: Some building codes also specify a minimum riser height, often 5 inches (130 mm).
4. Riser-Tread formula: Sometimes the stair parameters will be something like riser + tread equals 17–18 inches (430–460 mm)] or another formula is 2 times riser + tread equals 24 inches (610 mm). Thus a 7 inches (180 mm) rise and a ten inch (254 mm) tread exactly meets this code. If only a 2 inches (51 mm) rise is used then a 20 inches (510 mm) tread is required. This is based on the principle that a low rise is more like walking up a gentle incline and so the natural swing of the leg will be longer. This makes low rise stairs very expensive in terms of the space consumed.
5. Maximum nosing protrusion is typically 1.25 inches (32 mm) to prevent people from tripping on the nosing.
6. Height of the handrail. This is typically between 34 and 38 inches (860 and 970 mm), measured to the nose of the tread. The minimum height of the handrail for landings may be different and is typically 36 inches (910 mm).
7. Handrail diameter. The size has to be comfortable for grasping and is typically between 1.25 and 2.675 inches (32 and 68 mm).
8. Maximum space between the balusters of the handrail. This is typically 4 inches (100 mm).
9. Openings (if they exist) between the bottom rail and treads are typically no bigger than 6 inches (150 mm).
10. Minimum headroom
11. Maximum vertical height between floors or landings. This allows people to rest and limits the height of a fall.
12. Mandate handrails if there is more than a certain number of steps (typically 2 risers)
13. Minimum width of the stairway, with and without handrails
14. Not allow doors to swing over steps; the arc of doors must be completely on the landing/floor.
15. A Stairwell may be designated as an Area of refuge as well as a fire escape route, due to its fire-resistance rated design and fresh air supply.