To install engineered hardwood flooring over a basement slab, can I use (2) 3/8″ CDX plywood over 1/2″ XPS?
QUESTIONS: Can I use 2 layers 3/8” CDX Southern Pine plywood (joints staggered, glued & screwed together, but NOT mechanically attached to the slab) over 1/2″ XPS? Whether I install the plywood sheathing over a vapor-retarder or rigid foam insulation, is CCA treated plywood necessary in either case? Which installation method (e.g. rigid foam or vapor-retarder) do you recommend in view of my concerns below?
DETAILS: I live in a condominium built in 2002 in region 5A (near Detroit), with a 8′ poured concrete full basement. The basement has an existing finished bathroom with a threshold height of 1-1/4” above the concrete slab.
I will be finishing the remaining basement space, and would like to install pre-finished engineered wood floors. I have read FHB 248 “Build a Risk-Free Finished Basement, FHB 169 “The No-Mold Finished Basement,” FHB 206 “A Wood Floor That Can Survive Anywhere,” and Building Science Corp’s 0308 “Renovating Your Basement.” Each provides very informative, but slightly different approaches to finishing basement spaces. I do not want to cut corners by skimping on necessary materials for a mold-free sturdy floor installation, and am also concerned with minimizing VOC’s and the floor transition at the existing bathroom threshold. Therefore, I like the minimal thickness accomplished by 2 layers of plywood over a vapor-retarder as detailed in “A Wood Floor That Can Survive Anywhere,” but see the benefits of a ‘breathable’ installation over rigid foam insulation detailed in the other articles. Which should I do, and what are the minimum materials that I should use?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part