Cool game. You forgot to put the background music on loop and when paused the game, I went to get a cup of tea. I came back and ambience was completely quiet, just zombie growls here and there. Also I ran/vaulted all of them and went to room 3. Then of single box I jumped/crawled into pipes an ran straight for room 7 as per notes.
In that room I found a secret zombie meeting place and joined them. Surprisingly, They did not attack me, just stood there and I couldn't go back up nor open the door from this side (I guess). All in all, impressive visuals. Good Game.