Thx rEdrUmMDK that's what i needed to now :)
This wil make my map faster .

So can you make an entire building Detail, if you cannot enter or go on its roof?? Its just taking up space like a model

After thinking on that a minute if this building is Structural it may block tris which might speed up your fps but might take longer to compile. If you make it Detail it will not block tris and the whole map area behind the building will be drawn in game and could slow down the fps.
If I am wrong someone else please join in and straighten me out. And please feel free to make comments. hehe

You are correct Red... as long as your also not dealing with transparent textures, windows and doors that aren't placed with node divisions in mind.

This is why you see so many halls that are shaped like an S or a T. This stops the game from thinking the player can see around the corner... thus the stuff around the corner is not drawn. The more of the map that has to be drawn all at once, the harder it is for the game engine handle... and then your FPS drops.

Thanks Red and Foyle for saying that. I've always dissagreed with those people who say make your whole map detail then just structure things you are going to attach portals to. I've left some roof overhangs structure because I thought (apparently correctly) that they would server to block vis.

Cheers m8

So what about internal walls of a building? Should they be made detail providing they don't host any portal boundaries?

Is there a downside to using too many detailed brushes?

Does it make the map run faster?

Thanks in advance :-)

but they do provide a means of blocking vis. In most cases, the room around the corner in a building is not drawn by the game because the vis is such that the player can't see it. This is providing alot of help to you.

Also, if a player can see from through a window on one and and back out another window on the other end, then everything on the other side of the building is being drawn. Depending on the layout of your map, this is a big advantage as well.

Detail brushes make your bsp filesize smaller and the compile time lower. It does not make the map run faster.

Ok so I went into the buildings I'm working on and turned things like stairs, stair rails, crates etc into detailed brushes. My BSP file size went from 1.9mb to 4.01mb, thought i was supposed to make it smaller? :(

generally it does. Perhaps when you turned the stairs into detail brushes it opened up the area on the other side of the stairs to the players view (according the the game engine).

So in general, it's best not to go too over the top with detailed brushes? I appreciate your help foyleman :)