Hello there, I have a quick question.
What brush entity is needed to prevent fog to appear within it's volume?

Thank you for answering :)

You will need to use fog_volume tool texture and make a brush. Also if i remeber correctly, you need to have secondary fog entities which the fog_volume brush is refering to.

Can this be used to make outdoor sections not have fog too? I have large areas where I don't want fog outside but would like it elsewhere, this possible?

But I'm using an env_fog_controller

Yup. If you already have a master env_fog_controller (as in, your "default" fog has the "Master" flag checked), then just make a second env_fog_controller, make sure the Master flag is not checked, give it a name, and give it whatever fog style (or lack thereofof) you want.

In areas where you want to use a different fog, draw a volume textured with fog_volume and tie to entity fog_volume, and put your "empty fog"'s name in the Fog Name field.

Or you can adjust your fog entities fog density and when it starts and ends.

Nice! I shall try all this out soon.

Thank you, this really helped me out!

Is there any way to smooth the transition? My building is so large that you can see fog inside the building as you walk up to it, but the trigger for fog volume is in the doorway so the fog abruptly vanishes as u walk inside...