I want to install a nailed down hardwood floor in a bonus room above my garage. The problem I am having is figuring out how to do this with the steel beam running down the middle of the floor. I currently have 1/2" subfloor installed. The top of the beam is raised up from the existing subfloor from 1/8 to 1/2". I will be adding another 3/4 subfloor on top of the existing subfloor to strengthen the floor since I will be running the hardwood parallel to the joists. I obviously cannot run the 3/4 over the beam since that would create a hump in the floor. I was thinking of running the ¾ to the beam then filling in the 8” beam span with lauan plywood glued down. The problem with using plywood on the beam is that the beam is does not have an even reveal to the subfloor meaning I would probably then have to go back and sand down the lauan in places where it was raised above the beam. The other idea I had was to fill in the beam as close as possible to the top and then pouring in a floor leveling compound. I know that I will not be able to nail down the hardwood over the beam but an 8” span between fasteners does not seem like a problem. I would probably use a subfloor glue in that area to ensure a good hold to be safe. Any suggestions would be greatly appreciated. [img]c:\temp\beam.jpg[/img]

I would run the ply up to the beam and just fill in the space with luan and maybe some felt. then just space your nails over. I wouldnt use self leveler or the like as it will bust and crack over time with movement.

Thank you for the reply Kevin. Do you know if there is anything I need to be concerned with in terms of moisture resulting from condensation on the steel beam? The underside of the beam is in the garage which is unconditioned space. I plan on putting felt paper over the entire subfloor.

cover it in felt like you would the rest of the subfloor floor and that should be fine.