Generally you would have separate layers for internal and external walls - but you don't need to if that does not suit the way you want to work.
But it will allow you to turn them on/off separately which can be handy.
That won't affect the automatic trimming though (but you can stop it - see below).
As mentioned the strength of the building materials used in the wall composites will control this.
Stronger building materials will cut away the weaker ones.
If your layers have the same intersection priority number, then building materials will trim automatically based on their strengths.
If your layers have different IP numbers, then the automatic trimming will not occur between those layers and the walls will ignore each other (not recommended unless you deliberately want to do this).
Also an IP number of 0 (zero) will mean that elements (i.e. walls) will not trim when in the same layer, otherwise elements in the same layer will always trim based on strengths.
Barry.
One of the forum moderators.
Versions 6.5 to 27
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