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Spiral stair layout without regrets
Just beam me up: Vertical access in limited space.
by John Corbett, Restoration Trades
Requiring only about half the floor area required for conventional staircases, spiral
stairs sometimes furnish the only legal means of access to upper levels, roofs and
lofts in areas where space is limited. Additionally, these prefabricated, freestanding
assemblies add a dynamic design element, save labor and relieve project schedules.
The labor and scheduling advantages of prefabricated elements come at a cost,
however. By their nature, these stairs are tightly configured to the space allowed
and once fabricated, they have little capacity to accommodate additional issues as
they arise. The step most critical to the success of the project thus becomes laying
out and ordering the stair itself. To find out how to get it right, we talked to a man
who consults on these issues every day, Rick Harrington, the manager of stair sales
for Steptoe and Wife, LLC, of Toronto, Ontario. Steptoe builds a period cast iron
stair, but the principles will apply roughly to all spiral systems, whether fabricated
from wood, steel or concrete.
Spiral stairs compress a number of issues into a compact package. Mr. Harrington
recommends that his customers get to know the particular stair before committing
to it. By preventing misunderstandings, he helps his customers avoid unhappy
surprises. For example, he recently spoke to an architect whose San Francisco client
wanted to run a staircase from a first floor exterior deck to the second floor and
proposed supporting its weight by extending the staircase center pole, by itself,
down through the deck to bear upon a concrete footing below. In many spirals,
this center pole does indeed support the weight of the steps, but not in the Steptoe
version. Here, the load is instead transmitted to the floor through the stairs them-
selves, much as in a conventional stair system. The pole cannot be used to support
the load. By asking the question, this designer avoided surprising his client with
additional project costs. Regarding the structural needs of spirals in general,
Mr. Harrington reminds us that they are free standing structures lacking the lateral
stability of built in stairs. Not only should clients be made to anticipate movement
when climbing spiral stairs, it's all part of the fun, they can be told, but spirals
over twelve feet tall will require a degree of sway bracing. For a recent spiral built
to pass through a twenty-foot space, Steptoe provided this stability by furnishing
a landing area halfway up which tied into the walls and provided a small living area.
By understanding the structural requirements of the spiral installation, the designer
was able to incorporate them into the overall design.
Once paid for, delivered and sitting in the yard, the staircase belongs to the purchaser,
mistakes and all. The fabricator will rightly disclaim responsibility for confirming
dimensions in the field or for conformity to local codes. Nevertheless, Rick Harrington
makes every effort to smoke out misunderstandings by requiring the purchaser to
furnish such drawings as are necessary to define the space. The errors he most
commonly sees are normal, tape rule type miscommunications about how to measure
rough openings, whether they were made finished floor to finished floor, for example,
as required, or if they were instead made rough to rough, finished floor to subfloor
or something else entirely. Once Mr. Harrington has confidence in these dimensions
and in his understanding of the space, he will produce drawings of the spiral stair
installed, for the purchaser's review and approval. This is a final opportunity for the
purchaser to verify all dimensions in the field. The fabricator's drawing will also prove
useful in obtaining approval for the spiral design from local building officials. Local
codes place restrictions on the permitted uses of spirals and the only way to be sure
if your design conforms is to ask your inspector. Spirals seem to fall into a gray area
for some officials and it may not always be clear that a design will pass until it does.
The permit application process gives them a chance to make their contribution to the
design process and sometimes that is all that they need. Certainly, no order should
be placed until their approval has been secured.
Layout for a spiral stair can be as simple as the project permits. Spirals offer a great
deal of design flexibility both in that they can be rotated on their footprint to accept
traffic from any point of the circle and in that traffic can be made to ascend either
clockwise or counter clockwise through the shaft. These two options usually allow
the designer sufficient leeway to configure standard stair assemblies to fit any space.
To orient the spiral, traffic patterns at one end or the other of the spiral will be deemed
dominant and allowed to govern. For example, where traffic is to be conveyed from
a main living area to a loft, the requirements of the main area would likely rule. In such
a case, the bottom entrance to the stair passage would be oriented to best expedite
traffic flows and victory is declared. All that remains to do is to provide a landing
deck or plate connecting the uppermost step tread with the main loft floor area, taking
care only that the landing material is not so thick as to impinge on the minimum height
required by code for the stair passage way below.
But what if the project requires a specified orientation of the passage at both top
and bottom of the shaft, whether because of code, clearances or customer preference?
Is there any way to adjust the relationship between the orientation of the top stair and
that of the bottom? There is, at some cost and with a little tinkering. Steptoe's stairs
perform one complete rotation every thirteen steps, winding twenty-seven degrees
around the center pole at each step. A climber's orientation when reaching the
uppermost step will be determined by the number of steps it took to get there.
For every twenty-seven degrees that we need to advance or rewind the orientation of
that topmost step, we must add to or remove one step in the series while maintaining
the same overall stair height. Steptoe accomplishes this by introducing shims
between all the assemblies to make up a step or by milling down the cast iron tread
assemblies to make room for one. These are the same methods Steptoe uses to make
the incremental adjustments to tread heights necessary to fit a stair into any given
vertical opening, but adjustments for this purpose are minor, a quarter inch or less.
The milling of the iron step assemblies necessary to create space for a whole
additional step will be much more substantial and will constitute a significant additional
expense. Also, with the addition of a step, the overall length and shape of the spiral
will be altered. A standard tubular handrail will no longer follow the pattern so the stair
must be fitted with a custom handrail at additional expense. Deviations from the
standard staircase pattern will entail additional cost, but given the full range of design
variables available, a spiral configuration can be developed to accommodate almost
any design requirement.
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