I have a house built in the 40's the hardwood is disgusting. We like a more contemporary/modern look. So we bought a 5 1/4" wide solid bamboo stranded. I don't want to pull up all of the old flooring as it is directly sitting on the floor joice. However I don't have enough height in under the new front door that we already installed to go over the old floor with 3/4" plywood/osb and then la the new flook on top. (All of the other doors on the first floor i could cut except for the new front door. So trimming all of the doors & jams to allow 3/4" plywood/osb Isn't an option) Would it be acceptable to lay 1/2" osb/plywood over the 3/4" hardwood attached directly to the floor joyst as a sub floor? And if so how do I get the vents/duct work to extend up to the new flooring?