Vapor barrier on second floor?

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Q: I’m installing 5/8 engineered hardwood floor on second floor over 3/4 plywood. These are 7 1/2 planks. Do I need to install a vapor barrier? We are nailing it with 1 1/2 inch L cleats. Is this workable over floating the floor or gluing it? How does a wood floor expand when nail tight to a plywood floor? How can it move without the plywood moving?

A: Well, the product is engineered which means it is suppose to be, because of it’s construction very stable. You should not need a vapour barrier on the second floor. In fact, if it is nailed down and you are punching a thousand holes through such a barrier, how can it be a barrier? As to specific installation instructions, there is so much variation from one product to another, it is best to follow the recommendations of the manufacturer.

Solid wood floors are more of an issue in significant humidity swings than engineered. And some species are more affected than others. I prefer cleats over staples because cleats allow some stretch or expansion of the floor board. Staples are more resistant and under sever conditions can cause splitting of the tongue. The wood floor moves separate from the wooden sub floor. This is why you can walk into any given building and see gaps between boards. Expansion and contraction.

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