Hello I'm using BIM for blender for creating a section plane. But After I applied temporary section plane I got some weird black artefacts. Any ideas How to fix it ?
This looks like the Cycles render engine ? For optimization purposes there is a limit to how many surfaces a light ray can go through. The temporary section shader overrides your materials with a transparent shader. Even though they are not rendered, the surfaces are still calculated. Black pixels mean the ray doesn't have any juice left and isn't allowed to go through more surfaces. Try increasing the transparent rays count in the render settings :
Note although doubling the count won't double your render times, it will take a longer time to compute.