Not much, I still find myself ducking a little when I walk past the roof hatch, but I can stand in the middle. My buss has a wooden sub floor but not sure how thick that is. Once the weather gets warmer here in N.J. I plan on remodeling the interior and taking up the floor is on the list. I plan on installing some type of noise insulation (I was looking into www.quietcar.net
) then I would think that the wood sub floor will have to be replaced. The roof does slope on either side. In the center it measures about 77" at about 2 feet from the side it measures about 74.5". Hope this helps.