Zombie Breakable Walls
1) Cut out a segment of your wall that you want to be breakable. Make this piece 128x8x128 units and tie it to a FUNC_BREAKABLE (ctr+t). Assign the material to WOOD, disable shadows, and make it breakable by ALL INFECTED
2) Copy the breakable wall over and make the new piece thinner then the original. I use 4 units here, but will decrease it to 2 later on in the tutorial. Get rid of the FUNC_BREAKABLE on the new piece by pressing CTR+SHIFT+W.
3) Use the clipping tool to cut your new piece in half vertically, and slice out strips horizontally based off the texture you're using (this makes it look really good).
4) Resize each individual piece to make them have different lengths. Make sure the bottom pieces are separated enough so the zombies can run through it cleanly.
5) Now use the clipping tool and vertex manipulator to make the edges of each piece look like they were literally snapped off. I made this whole thing 2 units thick here to look more like pieces of wood. After you get your desired effect, select all the pieces and assign this to a FUNC_BRUSH.
6) Open up the properties for the new func_brush. Name it breakwall_spawn, make it start disabled, disable shadows, and make it not solid (i prefer that but it's up to you).
7) Place the func_brush inside the func_breakwall so they're both even.
8) Place a prop_static behind the break-wall that is assigned the model "infectedbreakwall01_2x4mainframe01_dm.mdl". You also want to disable shadows on this and make it not solid.
9) Now place the prop_static inside the break-wall as well.. behind your func_brush.
10) Next open up the properties for your FUNC_BREAKABLE. Click the outputs tab and add a new output. Make it look like this:
My output named: OnBreak
Target entities named: breakwall_spawn (or what you named yours)
Via this input: Enable
Now you have a working wall that will break when hit by infected! Once it breaks it will spawn the broken up func_brush in its place! This looks very good in game and you can customize it to work any way you want. You can test this in game by pointing at your break-wall, opening console and typing "ent_fire !picker break". ENJOY!