I would like to do myself a wood spiral staircase for my country house
The diameter should be 4' and the high is 8'
How many treads should I take into consideration? What should be the
angle between threads? (Is 30 deg. correct?)
How should I do the curved rail?
Or could you suggest me some technical specification.
Take a look at:
"R314.5 Spiral Stairs.
Spiral stairways are permitted, provided the minimum
width shall be 26 inches (660 mm) with each tread having
a 7-1/2 inch (190 mm) minimum tread width at 12 inches
(305 mm) from the narrow edge. All treads shall be
identical, and the rise shall be no more than 9-1/2 inches
(241 mm). A minimum headroom of 6 feet, 6 inches (1982
mm) shall be provided"
Getting the required headroom means that you have to
go up at least 9 risers before you overlap the landing
below, which strongly militates for 3 steps per quadrant,
or 30 degree wedges. 11 rises and 10 treads gives
you 8.73" rises and a landing that's a 60 degree wedge
with the required headroom.
The 7.5" tread-width at 12" from the inner edge
means that that walk-line needs to be
7.5 x 12 = 90", which means that your
center post pretty much HAS to be at least 3".
Was I you, I'd give some serious thought to
using black-pipe as the center-pole.
You might use 1.5" pipe with 2' 4x4 treads with a 1.5" vertical hole 4"
from one end and a 4"x1/4" horizontal bolt on each side of the hole to
squeeze the pipe. The "handrail" might be 1/8" plastic covered aircraft
cable threaded through the other ends, anchored at top and bottom, with
a turnbuckle to keep the cable tight.
It was known across the nation as "The Cook Creek Spar Tree"--the
most ingenious fire tower ever. It stood within the Quinault Indian
Reservation 9 miles southwest of Lake Quinault.
In 1927 a 179' Douglas fir 7 feet in diameter was high-topped by a
Hobi Timber Company climber using spurs and a crosscut saw. The huge
pole was then debarked with a double-bitted axe as he descended from
the top. Three-foot steel rods with an eye in one end were driven
into the tree in such a manner as to form a winding staircase with a
steel cable threaded through the 130 eyes and stretched taut with a
chain binder. The tightened cable served as a hand rail, as well as
to hold the rungs securely into the trunk. Four railroad ties were
then anchored a few feet below the top, with the 49-square foot house
assembled atop them by Paul Meyer and his two helpers. Cedar shiplap
siding finished the walls, and sliding glass windows gave the eagle's
aerie its own touch of class.
Upon nailing on the last shingle, Paul stood up on the rooftop and
hoisted the American flag. His shouts could be heard only faintly
on the ground as he declared, "I can see all the way to Hawaii." For
the next 28 years the unique fire tower stood. No one ever challenged
his statement by climbing atop that breezy roof again.
During its years of service, the Cook Creek Spar Tree became a center
of nationwide publicity. Newspapers from coast to coast ran feature
stories, and in 1929 Hollywood newsreels portrayed it as the phenomenal
In 1955 the Bureau of Indian Affairs found it necessary to saw the
pole down for fear that someone might be injured climbing the decaying
attraction. Today, nothing can be found but a few rusted fragments
amid a thriving new forest in the NE1/4 of the NW1/4 of Section 26,
Township 22 North, Range 11 West.
From "Fire Lookouts of the Northwest,"
by Ray Kresek, Ye Galleon, 1984.
This is a great question, and I wish I could help you with this
project. It sounds fun. Okay, you need to first figure out how many
stairs you will have.
Determine number of stairs: Take total height and divide by 7" (this
is the ideal stair height). You will most likely not get an integer
number. So, round it either way. Let's call this number N. Now
divide your total height by N. This is how tall each of your risers
will be. The total number of stairs you will need will actually be
N-1, because the floor at the top of the stairs will serve as the last
Determine the angle: 30 degrees sounds about right, but I don't know
this one for sure. But I would say that once you begin, it will be
tricky to make sure your last stair ends up in the right location
relative to the second floor. I might be inclined to start my layout
from the top stair.
The curved rail is the biggest challenge here. I once built an
elliptical-shaped wall cap, and I did it using a large (very large)
scribe. I actually used an existing curved wall, and then drew the
pattern on the side of the wall, and then built the wall cap against
the wall. This information is probably useless to you. But I would
probably build a cylinder of the appropriate diameter. You can do this
with plywood plates and studs. Then I would use this as my model and
go from there. Hopefully someone else will have a better answer than
Good luck, and have fun.
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