I've been working on close stringers for curved stair cases.  The circular variety is pretty much figured out but the elliptical variety still needs an instantaneous adjustment to the stringer depth since the pitch angle of the stairs (slope) is constantly changing.  The geometry of a 0.9 eccentric ellipse shows off this distortion quite well.  I will hit it again tomorrow and see if I can't figure out a more accurate algorithm for these stringers.  Sometimes I enjoy a good challenge, but this one has certainly had me scratching my head a few times already.

Tutorial 87 - Curved Stairs (9:20 min.)

**Version 4.5.9** - 05.31.2026
- Added two new parameters for elliptical curved stairs into the draw and edit menus: Eccentricity, Clocking.
- Enabled treads, risers and framing (primitive) for curved (elliptical) stairs.

Version 4.5.7 - 05.26.2026
- Enabled presets for posts.
- Added the following L.J. Smith handrail profiles: 684, LJ6011, LJ6A10.

For those interested I am pulling all of my handrail geometry from LJ Smith's webpage at the following link:

https://www.ljsmith.com/handrails

Version 4.5.6b - 05.25.2026
- Enabled presets for stairs.

Version 4.5.6 - 05.25.2026
- Enabled presets for beams.
- Enabled presets for in-wall columns.

Version 4.5.4 - 05.22.2026

- Added an option for a top and a bottom baluster shoe.
- The top baluster shoe can be controlled with the additional "shoe height" parameter, which in turn allows for baluster collars.
- Added the shoerail offset parameter to vertically offset the shoerail.
- Fixed a bug in the railing edit menu with metric units.

Version 3.8.1 - 05.13.2026

- Enabled a second layer of wall sheathing for common and scissor trusses.
- Enabled XPS (blue, green, pink and grey), ISO, EPS, GPS, and PU foam insulation within the wall sheathing and wall sheathing 2 options.

Each girder will break up the roof outline into zones.  Then using a combo of boolean subtraction and intersection we should be able to generate this as a starting point:




The blue shaded truss outlines are the girders, the purple shaded are the trusses requiring a further subtraction step to make the correction for the valley truss sets, notice the third purple truss  from the right. 

Basically I'm walking you through my algorithm for generating the truss geometry data so I can then draw each truss.  As you can see this is not a trivial process.  Lots of steps and lots of "edge cases" that can potentially trip it up.  That is what I mean when I say the devil is in the details.  However if the basic algorithm is sound one should be able to add in logic to deal with the issues and in the end you end up with a robust piece of code.  These are the kinds of things that keep me up at night.

Based on these slices we should be able to extract the key geometric points that define each truss and then send that data to the separate truss "draw" algorithm which sorts out all the messy details on how to place the webs, plates and all that fun stuff.

Here is a simple schematic of a slightly more convoluted roof to try and understand the methodology a bit better:

The two girders in the center of the structure could probably be combined into one larger girder, but maybe it is better to distribute the loads across to trusses instead of one.  The shaded areas are the valley sets or overframing required to fill in the voids.

This design requires 10 main girders and 5 cross girders.  Notice how there is a hip truss at each outside corner and a half valley set at each inside corner.  When to inside corners are symmetric we end up with a full valley set.

Based on these patterns that are emerging I might be able to auto place the girders or at least provide an initial placement which then can be further refined by the user.