ok Maybe its me but why go through all the hassle of building this closet sized area into a safe room when you should just build a safe to fit the area? For instance why dig the floor out when you could just put 3/16 steel plate for the floor and all other sides welded into a box then a couple rows of drywall then another box of 3/16 steel and weld your door to it then all you have to do is bolt it if you want to, to the floor(which I agree will move with expansion). Point being with a floating floor why make the safe a part of the house when I think it would be easier to just make a jumbo sized safe that only attaches to the floor. The other reason I ask this is because I have been contemplating a similar idea in my house? what do you think? Also I am in DC