The firebox is fire brick. The cook chamber is Hardie Board. Did some research and it's not supposed to off gas until much higher Temps when all food would be ruined anyway.
That is nice. I have a back yard space that I laid out to build in my bbq's under the awning years ago and never finished it. If I could steal your whole thing and set it in my yard it would be ideal. Now you have my wheels turning again.