Modeling
About Archicad's design tools, element connections, modeling concepts, etc.

!Restored: Flaw in stair logic

Anonymous
Not applicable
The problems with the stair tool stem from a flaw in the logic. The stairs are being defined by where the riser is rather than where the front edge of the stair tread is.

In this post I've attached an image showing a stair that does not have a nosing overhang:
- the 3D matches the 2D; and
- the handrail is the correct height above the nosing of the stair (as stipulated by regulatory requirements).

In the subsequent post I will attach an image of the same stair with a 30 nosing overhang:
- the 3D no longer matches the 2D; and
- the handrail is no longer the correct height above the stair nosing.

These problems occur because the 3D of the stair is being generated by the outside face of the riser rather than the front edge of the tread. The nosing overhang is being added to the front edge of the tread instead of at the back where it should be, with the riser face moving back by the distance of the nosing overhang.

In the real world stairs are set out by their treads, not the risers, and the locations of all of the other elements of the stair is determined relative to where the treads are located.

I'm really surprised that a program as mature as Archicad 11 contains such a fundamental flaw in its logic. It is not reassuring.

Stair without nosing overhang.jpg
52 REPLIES 52
Anonymous
Not applicable
The reason it doesn't model winders correctly is entirely due to the logic flaw I am referring to.

The programmer obviously doesn't realise that in real life it is the tread that drives the stair, and that when a nosing overhang is added the leading edge of the tread should stay where it is and the riser face should move back. What he has programmed keeps the riser where it is and the front edge of the tread is moved forward. This totally screws the winders up. It also makes the height of the handrail incorrect.

All it does is prove that the programmer responsible doesn't understand how stairs actually work. Therefore is anybody really surprised that other aspects of the stair also don't work as they should.

The fact that this logic flaw occurred at all and still persists is an indictment on the Graphisoft QA system.
Anonymous
Not applicable
The International Building Code (which all of Caif. and where the entire U.S. is not only headed, but is almost there), (we use to have three different primary codes), does not require nosing on R-3 (residential) stairs which are not "solid". Section:1009.3 exception 4.

So, if I'm laying out stairs and I have say 90" of travel to cover and there are no other overhead or other constraints, then I set the real treads on a framing square to 10": and I get..(you guessed it) 9 treads on the "horse".(risers to code) I don't have to have a nosing, so if I do add it, up to 1.25" it really does not matter. So I have to conclude that I don't want the nosing to adjust the stair. It's totally my prerogative if I want a nosing and does not effect the placement of the "horse" (carriage). And.. on a corner,(winder or not) the nosing, should I choose to add one, can extend past the corner turn, (just like the handrail) up to 1.25"

I'm sure other places around this round ball we all live on are different.
So, my point is this, ALLOW US TO OVERRIDE the "logic".
So G.S. in this case, when I'm driving and we're coming to a curve, PLEASE take your hands off the wheel! Thanks.

If the logic will allow me to build the total death stair shown in my last post, then why have this stupid pop up tell me I can't build a stair that I know is legal?

Bier
Anonymous
Not applicable
Thanks for restoring my post G.S.
I thought you deleted it because of my comments.
Bier