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2x8 Floor Joists 1/2 Pex with Heat Transfer Plates - Faced or Unfaced Fiberglass

cloves Member Posts: 16
Hi everyone,

I am in the process of installing pex throughout the house (including the basement). Now the floor above the basement (aka 2nd floor in split), is staple up 1/2 pex with aluminum heat transfer plates. The floor joist are 2x8, two lines of pex in each bay. What is the general recommendation for the the type of insulation to use and the amount of space to leave?

Is 2 inches of space and r-13 fiberglass below the norm? I have read that too much space is just as bad as not enough.


  • Paul Pollets
    Paul Pollets Member Posts: 3,523

    An air gap is not really required between the plates and insulation. R30 is usually required if garage is unheated, but you won't be able to cram the batts in an 8" space. I'd consider rockwool batts which have a higher R-value than 6" fiberglass batts (R21).
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Depends on the type of Plate

    If you're using the extruded alum plates such as Uponor/Wirsbo Joist Trak no air gap is required. Heat transfer is direct from plate to floor. The benefit, quicker floor response time, lower water temp and even floor surface temps. Min insulation required is R11 but insulation is our friend so the more the merrier..Could care less about type its all about


    If you're using those cheap tin plates, yup need the 2" air gap. But you'll give up the benefits of the extruded plates.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."