Location and access for your spiral staircase: The best location of your spiral stairs will usually be in an area with the most convenient access on the upper floor. Your decision may also be guided by where you think the new stair would best highlight your home’s interior.
The new stair will require easy access at the top and bottom floors. Both the location of each access and the directions you will walk to and from the stair are important.
Be prepared to be flexible with these early considerations. Your spiral stair diameter, the floor height and nearby obstructions on either floor may dictate placing or rotating the stair differently.
Treads for different spiral stair diameters may turn different angles, changing the amount of total turn for the entire stair, meaning you will get to the top in a different spot.
Your floor height will determine how many treads you will need, again how far the entire spiral will turn.
Obstructions might include, among other things, nearby walls, windows, doors, built-in furniture, lighting fixtures, ceiling fans, or fire places. The spiral stair itself may become and obstruction, say if one of the access locations is in a blind corner of two walls so that you have to crawl under the spiral to get on.
Headroom above any part of the spiral must be sufficient so a tall person will not have to duck when using the stair. Examples of headroom extremes might be going up the spiral along a sloping A-frame ceiling or passing a twirling ceiling fan. You might have to be careful if your spiral exits at the top floor under a sloped ceiling or ceiling beam.
You spiral stair manufacturer routinely deals with these issues and should be able to guide you on what is possible. Your final plan must accommodate all these considerations.
To see for yourself how obstructions may come into play, imagine the spiral stairs as a cylinder sitting on the lower floor. It may help to place a cardboard circle on the floor to represent the cylinder’s lower end and imagine the curved walls going up.
The cylinder should have the same diameter as the recommended stairwell dimensions. Your manufacturer should be able to supply this dimension. If not use the actual* diameter to the outside of the spiral handrail plus about 4” for finger clearance.
The imagined cylinder should rise all the way to the top floor without hitting any obstructions. The spiral stair’s top tread will end a little farther from the floor edge than half the cylinder diameter. A landing that is part of the stair will reach out from the floor to the top tread. Headroom constraints under the ceiling over the top floor should be apparent above the top tread and landing.
*Actual diameter may not be the nominal diameter…i.e. a 6’ nominal diameter spiral may actually be 5’ – 8” to the outside of the spiral handrail.