I've been reading a lot of threads on here about building a smokehouse, My main concern is preventing it from starting on fire. I see some that have have issues with this. What is the consensus on fire retardent materials for the inside of the house? I see a lot of people using Durock, but will I need a gap between the Durock and the wood? I plan on making it ~3'x3' and 4'-5' tall. My goal is to be able to cold smoke and then finish the meat in the same smoker. Any suggestions are appreciated.