I have a solid, (non composite), slab intersecting a composite wall. When using a solid element operation to subtract upward extrude the slab from the wall it subtracts only the outer skin of the wall. if I change the slab to a composite it extrudes the whole thing wall. I don't want a composite slab but I do want to subtract and extrude from the whole wall.
Slabs and walls automatically trim each other based on the Intersection Priority strengths of the Building Materials.
The problem you are having is that the strength for the BM of the slab is stronger than the BM for the outer skin but weaker than the BM for the inner skin.
So the wall is cutting the slab away automatically at the inner skin - so there is no slab left to do your SEO with upward extrusion.
You need to make the slab BM stronger than the wall inner skin BM (be careful as this may affect other connections) or change the slab BM for one that is already stronger.
One of the forum moderators. Versions 6.5 to 25 Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10 Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10