topic Re: Stair with First 4 Treads Compensated, Then Normal in Modeling

Stair with First 4 Treads Compensated, Then Normal

Heftor — Tue, 25 Nov 2025 14:52:05 GMT

Hello everyone,

I'm trying to model a stair where the first four treads are "compensated" (meaning the nosing is adjusted to fit a specific landing or winder condition), and from the 5th tread onwards, they are standard, equal treads, like the floor plan below.

I'm working in Archicad 28 and using the Stair Tool. I can successfully create the compensated treads and risers by dragging the nodes in the floor plan, but the problem is that the stair's underlying structure remains unchanged, which causes issues for the rest of the flight.

Is the best approach to model this as two separate stair elements? Or is there a way to define a "transition node" within a single stair object where the tread compensation stops and the structure recalculates for standard treads?

Does anyone has any experience in this?

Thanks in advance.

Hector

Operating system used: Windows

Re: Stair with First 4 Treads Compensated, Then Normal

Yves — Tue, 25 Nov 2025 16:54:29 GMT

A little tip by Noémie shared on the French forum Archi-CADlink

https://youtu.be/8I4PLZBbuUc

Betreff: Stair with First 4 Treads Compensated, Then Normal

runxel — Tue, 25 Nov 2025 20:08:38 GMT

Great link, Yves! Beat me to it.

Basically, the a bit unintuitive rule here is that whenever you encounter stairs with winding steps at the landing you have to make sure the "actual" direction (as in running direction, "Laufrichtung" in German) of the beginning tread/riser needs to be perpendicular to it. It's just something you need to internalise, then it comes natural.

So, think from the "inside" out, not from the boundary (which would make this example a straight run) inwards.

It also helps to place some 2D guard rails before hand to figure out the construction.

Re: Stair with First 4 Treads Compensated, Then Normal

Lingwisyer — Wed, 26 Nov 2025 02:03:56 GMT

Curve your walking line so that it still follows the rules you have set, then trim the edges. Though, given your dimensions, you have a fixed inside and outside tread width? So your walking depth changes?

Re: Stair with First 4 Treads Compensated, Then Normal

Heftor — Fri, 28 Nov 2025 09:22:56 GMT

Hello All,

I'm following up on a previous tips and video about creating a stair with compensated treads. With your help, I've managed to compensate the treads and risers successfully, and the 2D symbol and the stair's top surface.

However, The structural component of the stair I cannot modify it. It remains shaped as if the stair were still tangent, creating a conflict between the tread-riser and structure.

I see that the base line is still tangent

but when I make it a straight line it unmade the steps 😓

I'm starting to think the issue might be that my initial tangent curve is too steep or extreme for the Stair Tool to cleanly generate a transition to the straight run.

Has anyone encountered this and found a solution? is there a practical limit to how much you can compensate a tread before the structure fails to follow?

Thank you.

Hector

Re: Stair with First 4 Treads Compensated, Then Normal

Barry Kelly — Fri, 28 Nov 2025 09:37:44 GMT

The trick is that the path or reference line of the stair remains curved.

That is the single blue line you are adjusting in your image - don't do that.

You need to adjust the 'Boundary' lines.

Select the stair on the other side or you can use TAB to cycle selection.

So you are adjusting the shape of the stair boundaries while actually still having a curved path.

Barry.

Re: Stair with First 4 Treads Compensated, Then Normal

Heftor — Fri, 28 Nov 2025 09:48:47 GMT

Hi Barry,

I already did that and the structure boundaries are straight but the steps on the structure are not.

As you can see on the screenshoot below:

Regards,

Hector

Re: Stair with First 4 Treads Compensated, Then Normal

Barry Kelly — Fri, 28 Nov 2025 13:03:42 GMT

Try pulling the front node of the reference line to the side so the curve is tangential to the vertical line above.

Barry.

Re: Stair with First 4 Treads Compensated, Then Normal

Heftor — Mon, 01 Dec 2025 08:13:09 GMT

Hi Barry,

Indeed, I can change the the line reference to make it tangencial to the vertical line:

but this way i cannot have control where the steps start. Now the orientation is good but the I have 2 extra steps:

and adding a extra part of the estructure.

Regards,

Hector

Re: Stair with First 4 Treads Compensated, Then Normal

Lingwisyer — Mon, 01 Dec 2025 08:57:42 GMT

Click on the opposite boundary, you should get two green reference lines which you can edit to change the actual bounds of the stair. The video that Yves linked shows the whole process pretty well.

Re: Stair with First 4 Treads Compensated, Then Normal

Heftor — Mon, 01 Dec 2025 10:26:19 GMT

Hi @Lingwisyer , @Barry Kelly, and all,

Thank you both for your replies and for linking the video. I appreciate the help.

I believe I’ve hit a more specific constraint. The techniques shown (and in the linked video) work perfectly for designing a new stair freehand, where you can adjust the boundary lines freely until it looks right. Like this one I just made

My situation is different: I am redrawing an existing stair from precise field measurements. I have fixed dimensions for:

Total rise and run.
The exact geometry of the compensated treads.
The exact point where the stair transitions from this curved start to a straight run.

When I follow the standard method—adjusting the boundary lines while keeping the stair path (blue line) curved—the structure still fails to match the tread and the rise finish.

My Question: Is there a way to force the stair's structural geometry to strictly follow user-defined node placements on the boundaries, even if it creates a more complex or less "ideal" transition? Or, when documenting an existing irregular stair with precise dimensions, is the accepted workflow to:

Model the treads/risers with the Stair Tool for scheduling.
Then manually model the actual, as-built structure/soffit using the Morph tool?

I’ve attached a portion of my blueprint with the key dimensions highlighted. Any guidance on the best practice for accurate documentation (not just design) would be incredibly valuable.

Thanks again for your time.

Hector

Re: Stair with First 4 Treads Compensated, Then Normal

Barry Kelly — Thu, 04 Dec 2025 08:05:34 GMT

@Heftor wrote:

My situation is different: I am redrawing an existing stair from precise field measurements. I have fixed dimensions for:

Total rise and run.

The exact geometry of the compensated treads.

The exact point where the stair transitions from this curved start to a straight run.

When I follow the standard method—adjusting the boundary lines while keeping the stair path (blue line) curved—the structure still fails to match the tread and the rise finish.

Looking closer at your images, the dimension on the right side of the treads all appear to be the same ... 170mm.

If these are being generated from a curved stair structure where the treads emanate from a single centre point, this will not be possible.

As you can see in your last image.

So, this method only works if your treads emanate from a single centre point.

The equal treads in your example will all have separate center points (or pints of origin).

Rather than a circular or spiral beginning to your stair case, you can have winders with varying origin points.

Something like this, but I just don't know how to incorporate a winder into your stair.

I don't model a lot of stairs and when I do they are not usually curved.

At the moment I can only suggest modelling those angled treads from separate slabs.

Barry.

Re: Stair with First 4 Treads Compensated, Then Normal

Heftor — Thu, 18 Dec 2025 11:47:45 GMT

Hello again everyone, especially @Barry Kelly ,

I'm writing to close this thread with the solution and to thank everyone—especially Barry—for the crucial insight that solved my problem.

It was possible to model the stair correctly from a single center point, once I understood how to define it.

In my earlier attempts, I was adjusting the stair's boundary lines and nodes based on my 2D plan, but I was doing so without correctly setting the stair’s actual center of rotation. As a result, the geometry was inconsistent, and the 3D structure would not update properly—it remained as if the stair was still purely tangent, even when the treads looked right in plan.

Barry’s last comment made me realize I wasn't defining the problem correctly for the tool. I went back and properly set the stair’s center point in the stair settings—aligning it with the real, physical center of the existing curved flight. Once I did that:

The treads automatically compensated correctly, I have to aproximate some measures.
The thread finish updated perfectly.
The transition from the curved start to the straight run was cleaner.

The key takeaway for others:
If you’re modeling an existing curved or partially curved stair and the 3D structure won’t follow your 2D adjustments, double-check the stair’s center point definition. The tool needs that reference to calculate the tread compensation and the structural soffit correctly. The boundary line edits alone aren’t enough—they have to work in concert with a properly placed center.

Thanks to @Yves for the video: https://youtu.be/8I4PLZBbuUc to correct the curve stair.

I’ve attached a screenshot of the final, correct stair, both in plan and 3D. The structure now matches the existing conditions perfectly.

Thank you again to everyone who chimed in. Sometimes the answer isn’t in fighting the tool, but in stepping back and making sure you’re giving it the right foundational information.

hopefully this helps someone else avoid the same head-scratching.

Best regards,

Hector

Re: Stair with First 4 Treads Compensated, Then Normal

Barry Kelly — Fri, 19 Dec 2025 01:30:52 GMT

So glad you got it working.

I kept having trouble getting the 5th riser to be horizontal and the curved goings (1,2,3,4) to all be equal.

I guess it is a case of knowing exactly where all the critical points are.

Then I just remembered you can model a stair from top to bottom.

You know the top start point.

You know where riser 5 is.

You know where the centre of the curved treads is.

That is all you need to know, the last point of the stair is automatic.

So in 4 clicks (5 if you include changing the pet palette), you can place the stair.

Barry.

Re: Stair with First 4 Treads Compensated, Then Normal

Barry Kelly — Sat, 20 Dec 2025 02:52:57 GMT

But as I look at this again, the riser between 4 & 5 is not exactly horizontal.

Maybe I still did not pick the exact points to get it all lined up properly.

It is close though.

Barry.