Does 3/4 plywood underlayment need to be separated from the floor joists?
3/4 inch plywood used as a subfloor is glued and nailed directly to the floor joists. Sometimes used as underlayment, plywood is nailed or stapled to the subfloor. 3/4-inch underlayment is rarely used but may be installed to make two different floors areas level with each other.References:Extreme How To: Install Plywood UnderlaymentResources:Floor Covering Installer Magazine: Panel Underlayment: What To Use And How To Use It.
