Spiral sizes defined: Most Precision Pine spirals are nominally sized according to the diameter of a circle approximately 2 inches outside the tread perimeters . The spiral handrail's outside face lies directly above the tread perimeters (see enlarged detail in figure 9). The 2" space allows the customer to place balusters outside the spiral rail and still have a small clearance.
Precision Pine recommends you use finished stairwell dimensions 4" greater than the nominal diameter to make the installation easier. For example, a 5'-0" diameter spiral has a nominal diameter of 5'-0", or 60". The recommended dimensions for a square stairwell would be 64" by 64". Sometimes smaller openings will work, but we should check this for you. See the space requirements for more info.
Figure 9.
How Precision Pine spirals are measured
5'-1" spirals are the exception to the
size definition: The only exception to this rule is with the 5'-1"
diameter, where the tread perimeters form a true 5'-1" diameter circle.
If you use a stairwell finished at 5'-1" the treads (and rail directly
above the treads) will contact nearby walls and/or the top floor system.
This leaves no room for your fingers. Codes require from 1-1/2" to
2" clearance outside the handrail for finger room so you can keep
your hand on the rail all the way up the stairs.
