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Intersection priorities help the user control interactions between certain elements. Wall and beam elements have their own intersection priority; I'm calling that the element priority. Composite skins (and components of custom profiles) have their own intersection priorities. Those are skin priorities. Neither of these should be confused with the intersection group number property of layers, though that bears on intersections too!

Element priorities effect plan and 3D geometry. Skin priorities effect only plan. Managing skin priorities is the key to proper automatic joint cleanup between composite walls in plan. Here's a look at the essentials of skin priorities and our standard composite setup.

Prerequisites

First, for skin priorities to work these conditions must be met:

• The intersection group number of the walls' layers must match.

• Reference lines of walls must meet.

These conditions are all old requirements for wall cleanup in Archicad. Skin priorities are intended to help graphically refine well-modeled intersections.

Skin Priority Behavior

Element and skin priority numbers range from zero to sixteen. Walls and wall skins use even numbers, while beams take the odds.

Priorities determine how skins meet. Fill names determine if skins clean up.

Skins with matching numbers meet each other, and will clean up if the fill names match.

Higher numbers override lower numbers. A skin will cross lower priority skins, and butt into higher priority skins.

Simple walls (no composite) still have an element priority. They should be set to properly interact with composite skins that they meet.

Skin priorities are ignored in 3D. Element priorities will determine the interactions of beams and walls. Therefore, composite walls need the proper element priority too.

It does not matter where the reference lines are, as long as they meet.

Illustrations
Simplified Composite
A simplified composite. Generally, priorities should rise toward the interior of the composite.


Priorities inside-out
Priorities inside-out
With lower numbers inside, the cores can't meet because the outer skins block them.


Meeting but not cleaning up
Meeting but not cleaning up
If the priorities match but the fill names do not match, the skins will meet but they will not clean up.


Matching names always clean up
Matching names always clean up
If skins with matching fill names touch, they will clean up regardless of priority number. The rubble skin with priority 8 cleans up with the rubble skin of priority 2.


Background pen override
Background pen override
If the fill names match but the background pens differ, the higher priority skin pen will override, while the fill pattern is continuous.


Bad existing wall
Bad existing wall
That's what's happening here. A new partition of 2x4s with priorities of 4-6-4 crosses an existing wall with priority 0, giving a confusing appearance.


Good existing wall
Good existing wall
Set the existing wall to priority 6 and the 2x4 partition stops as it should.


Element priorities in 3D
Element priorities in 3D
Element priorities control 3D intersections between walls and beams, and skin priorities are ignored. Even while you're using the skin priorities in plan, you need to set the wall's element priority with respect to beams.


Element priorities in 3D
Matching names always clean up
In a 3D document (AC12+), cut fills will clean up if the fill names match and the element priorities allow the fills to touch. But the skin priorities still do nothing.


Typical Priority Numbers

Generally, inner skins should have higher numbers than outer skins.

4 Drywall/Sheathing/Airspace Empty

6 Stud Space Empty

10 Masonry veneer

12 Concrete

And we have some space for expansion.

Stud wall framing follows a pattern of 4-6-4; Drywall/stud/[drywall or sheathing]

Veneer on CMU or concrete follows a pattern of 12-4-10; CMU/Air/Veneer

In existing construction, walls without composite applied (Empty Fill) should have priority 6, to cooperate with 2x_ composites.


See also: Composites: Why, How