Originally Posted by roach711
I put down 3/4" poly-iso insulation board with 3/4" tongue and groove flake board over it. Didn't want the insulation to get squashed down by us walking on it so I laid down some 7/8" pine runners to hold the flooring slightly above the insulation. I have a plywood floor in my bus so the runners and plywood flooring were screwed to the bus floor. I like screws better than nails because they hold way better and don't squeak when they work loose later on.
What Roach called "3/4 flake" around here is OSB. Using OSB in a floor is a bad Ida. It swells 10 times faster than plywood if exposed to any moisture. Anything pressed without a water proof glue, should not be used in a skoolie build. No MDF, OSB, that pressed crap for showers, ect.
This method has a flaw that most don't think of. If your pine runners hold your 3/4 plywood above the Styrofoam even a crack, that space becomes a cold zone and defeats the point of the insulation. Also the pine runners transmit cold directly to the plywood that transmits into the room.
As long as you get the good high density pink or blue, don't get the cheap white Styrofoam, it is rated for floors and will not compress.
A more effective system would be to leave the floor free floating. Lay all your Styrofoam tightly together. Next lay 3/8th plywood directly over it, making sure the joints are not in the same place as the Styrofoam joints. After you have that layer of plywood down, lay one more layer of 3/8th plywood, making sure no crack lays in the same place as the under layer. Now screw or staple the two layers together, and you have a perfect thermal break.
If your concerned about the floor moving, it won't. Just to be sure, some members on here have used a block of wood around 4" square in the center of each sheet of plywood, with 4 screws into the bus floor, and 4 through the plywood into the block to prevent sliding.
Now if your installing 3/4" hardwood, you don't need a subfloor nearly that thick. One layer of 1/2", or two layers of 1/4" would be more than enough. If you glue your hardwood down rather than nail, you can use as little as 1/4" single layer plywood.
Now for my Opinion
I hate the thought of wood in a floor. All wood has mold spores in it from the day the tree was cut down. Every time you mop, track snow in, spill, have a leak from plumbing or the roof, ect it causes the floor to start going bad. The makers of laminate flooring need to go to jail for life for making a inferior product that is made to fail, and ends up in our landfills in great quantity's. In as little as 24 hours after moisture exposure, mold starts to grow on the surfaces of the wood. In short, wood should not be in a floor.
My bus will have 1/8" thick steel as the subfloor over the 6" of Styrofoam. Flooring will be vinyl plank glued directly to the steel. Radiant heat lines will be resting in heat transfer plates right under the steel. Steel will not mold, and even if the paint fails, rust don't effect my health. For me I'm building in a bus because of the steel. I make my living building with wood, and see everyday how inferior it is. Our entire residential home building industry is 100 years behind.
Metal is always dimensional. When I order lumber on my job sites, over half is crap that is almost imposable to use. 20% gets burned because it's so twisted, we can't even use it for 14" blocks in the walls.
Last I just want to point out that I like to do things in a way that I never have to redo them. Any of the ways shown by other members will work, They just may not last as long. Me being too picky is why my skoolie is still not finished.