Hi. I have a home built in 2006 with an attic with nearly 20ft. tall ceilings. I've installed a pull down ladder so I can access this attic for storage. There is blown in insulation in the attic and the ceiling joists are exposed from the ceiling below. I'd like to put in a subfloor so I can easily walk around up there and also store items. Does anyone know what can be used for the subfloor, if I need to be aware of anything like jepordizing my R value of the insulation, wieght on the celing joists, etc.?