Hammer not compiling areas

Heres a screenshot of my issue, the red box is not compiling. If I noclip outside of my original area the other area is just not there at all and filesize does not change. I am attempting a map with separate closed areas connected by means of a mod. This is extremely frustrating and will ruin my map idea.

If anyone can point me in the right direction to fixing this, thanks.

First of all the box is not hollowed out. It’s just there outside of the playable area. It must be inside another hollowed out box if you want to look at the outside of it.

Secondly, if you want to make it a room and hollowed it out, you need at least one entity in there or it will be ignored.

Also there’s a thread for questions: http://www.facepunch.com/threads/1089229 (Why is it still not pinned on as important, everyone misses it?!)

You have to put an entity inside of it also.