Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Radiant floor between joists question

Hello new here and have a question, I'm a diy project guy and am currently putting an addition on the house I put the addition on posts,floor joists are 2x10 on 16" centers I'm looking at using oxygen barrier pex between joists with the aluminum plates. I'm looking at putting an r21 of spray foam over tubing is this a good thing ? House currently has hot water baseboard heat and will be using a mixing valve to lower temp in this zone and also will be putting baseboard in for a backup plan. Thanks for any input


  • delta T
    delta T Member Posts: 870
    Well, yes spray foam works great as an insulator (on a per inch basis), although IF you ever have a leak it is a real PITA to find and fix. If you are going with r21, I would stick to fiberglass batts, you should get an r30 or so with 10" fiberglass.

    Don't be scammed by the bubble foil reflective stuff, it is usesless as insulation.

    What does the flooring assembly look like?

    What kind/size boiler do you have, and have you done a heat loss calc on the house and the new addition? This is something I see a lot of DIY'ers skimp on, and it can lead to complications later.

    If you can draw a piping schematic (including boiler piping and other zones) of what you are thinking we can help you avoid common mistakes, and maybe make easy improvements to the system you already have.

    Welcome to the world of radiant!!