Solid element operations on a target using only one skin in a multi-skin composite operator

[Paul King]

Has anyone come up with a clever way to perform solid element upwards subtract extrusion operations on a target using only one skin in a multi-skin composite operator.

Materials in the composite operator element that I don't want to cut the target are set with lower materials priority than the target element material, and the material that I do want to act as a cutter has higher materials priority  - however when I attempt to use the operator on the target to do an upwards subtraction, the low priority material nevertheless cuts the target anyway.

No doubt I am missing something obvious here, but can anyone assist?

Crude markup below

This is a composite roof consisting of a plywood skin on an insulation skin, where I want only the plywood part to cut the rafters with upwards extrusion.

The red dots indicate extent of desired cutting of the rafters, and the green dots indicate the base of the rafters that should be left uncut by the operator element.

What actually happens is that the base of the cut is from the base of the insulation, even though materials priority of insulation is lower than for the rafters it is cutting.

[Paul King]

Thanks Eduardo - that would be a valid workaround  - but there are a lot of beams , and a lot of notching of beams in this project, and relying on manually sizing each notch/beam segment height under sloping roof elements would mean the cut notches could not update automatically when the roofing element moves, changes slope or size.   

In this case the roofing element represents the base of a gutter (one of many), each of which is set to a small fall.

[Eduardo Rolon]

After more careful though I deleted my comment (and you answered too fast) since it is a roof condition (not a slab) and I presumed your comment.

[Eduardo Rolon]

Using Openings might be an option since I don't think you can SEO with skins.

[Eduardo Rolon]

The bottom of the opening matches the Roof Pitch and it is relatively easy to edit in section

[Paul King]

Hi, yes, it could be an option for someone with an already resolved design - but the design is currently fluid, and I need a way to iterate to test the impact of changes to roof fall geometry on beam notching  - with a hundred beams, and many roof segments, and many ways to lay the roof and gutters.  The whole aim of the exercise for me is to let ArchiCAD do the work for each iteration.

I could have sworn that materials priority was supposed to take precedence when it come to SEO  

[Eduardo Rolon]

In that case then it might be easier to model the roof separately instead of using a composite.

Remember that Roofs do not work well with BMats which is the reason for the connect command.

[Paul King]

OK, the plot thickens - when I just view the roof element in 3D, materials priority is not leaving holes in the insulation where the beams pass through it.  So something else may be underlying the issue

The beams and the roof are on the same intersection priority in the displayed later combination, for what that is worth, but I must be missing something, because it seems material priority is not working at all.

[Paul King]

OK, a nasty workaround was to add another invisible skin on top of the roof composite  that has materials priority 999, then to select all beams and roofs and use Connect/Merge Elements - this gave the intended result in 3D (visually) - but then of course roof level markers give the wrong readings....

Yes, another workaround would be to use a simple roof rather than a composite roof for the cutting, and make a lower down copy of this, changed to insulation material as the insulation layer  - but then I would have two roofs to manage through each iteration I submit for discussion, and I would get a geometrically distorted result if I simply copied the same roof down and changed materials - because not all roof pitches are the same, and thickness of material needs to be measured normal to slope, not vertically - so junctions between roof planes at different pitches would need to shift around and be offset between one skin and the next - a horror show!

[Eduardo Rolon]

Remember the Connect-> Merge Command

The 2 cutting the insulation are merged to the roof.