First, a big thanks for this wonderful site!

You've clearly mentioned that Particle Board cannot be used as a subfloor for a nail/staple down installation of a hardwood floor, but does the same hold true for MDF (Medium Density Fibreboard) ?

I have a 1" (or 33/32") MFD subfloor that I'd like to staple hardwood flooring to. If MDF is as bad as particleboard, how thick of a layer of plywood would need to be added on top of this MDF subfloor?

Thanks in advance,
TC

I've never seen MDF used as a subfloor nor an underlayment. Kinda expensive for that. I'd double check. Do you mean OSB? If it truly is MDF, I'd think the same rules would apply as particle board. You would need a layer of 1/2" CDX plywood over it.

My mistake. I was peeking from underneath with a flashlight. The light beam made it look lighter in color and it looked like MDF. Its particleboard, so I'll be laying 1/2" CDX on top. Thanks for making me look again!

I think you need to look again. If you really do have 1" sub-flooring, and if it's osb rather than mdf or particle board, it copuld be acceptable.

Osb has large flakes of wood, probably nothing smaller than a silver dollar. Mdf and particle board tend to be made of very small pieces, like large pieces of sawdust, nothing bigger than a poencil eraser. Can you see any kind of grade stamp on the material? Maybe a brand name?