Installing PEX on wood subfloor. Pondering potential layering of / durock / pex / masonite?

slw4223

Installing PEX on a wood subfloor, planning to use 3/4 plywood with tracks cut in and reflective plates. (floor trusses will not support the weight of a poured cementious layer)

• Would there be a benefit of installing 1/2' Durock on top of the 3/4 plywood with pex? (creating a slight monolithic slab?)
• Finished floor will be LVP, so thinking to install 1/4" Masonite before the LVP

Thank you!

hot_rod

The Durarock would add a slight amount of thermal mass, but also some weight and small thermal lag, more r value to drive through

I would use an underlayment ply like Revolution Ply, Lowe’s sells it, instead of Masonite, in case it ever gets wet

Or the finish floor over the ply and tracks.

See what the flooring manufacturer recommends for under layment

slw4223

https://forum.heatinghelp.com/discussion/comment/1878726#Comment_1878726

Thank you, will look at the Revolution Ply!

Thoughts on placing Durock under the PEX vs on top? I had originally allowed 1 1/2" for gypcrete. We can carry an additional 7lbs per sq ft on the floor trusses, so the weight and thickness of the Durock is ok.

hot_rod

is the flooring a floating, glue down or nail down?

Generally those cement board products use a special coated drill point screw to fasten in or through them.

I doubt a hardwood nail gun would like the Durock?

slw4223

https://forum.heatinghelp.com/discussion/comment/1878742#Comment_1878742

Floating floor LVP

DCContrarian

https://forum.heatinghelp.com/discussion/comment/1878752#Comment_1878752

Make sure the manufacturer approves it for this application. Vinyl expands quite a bit when heated which can cause it to buckle. I know some LVPs are not approved for unheated spaces because they will shrink so much when cooled that the joints will come apart.

bjohnhy

I don't think you'll gain much with a layer of dura rock. Especially if the reflective plates are aluminum or such, to help distribute the heat.

It'll give youMore thermal mass, could be good or bad. But it'll also impede heat flow, (add r value) requiring higher supply temps for same BTU output.