On 1 Aug 2006 07:29:35 -0700, "Chris" wrote:

I would like to do myself a wood spiral staircase for my country house
(not expensive).
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:
http://www.postdiluvian.org/~mason/spiral/
and
http://www.downers.us/pdf_files/code...ODGIRC2000.pdf


"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.