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Insulating between conditioned and unconditioned spaces

user-5574861 | Posted in Energy Efficiency and Durability on

Climate Zone 4 – I am trying to finalize the details for insulating the floor/ceiling between 2 unconditioned spaces (garage/root cellar) and the conditioned spaces above them and a space conditioned to a temperature below the design temp of the house (wine cellar at 55 degrees).

Garage – Having lived in a house with a bedroom above a garage, I know how important it is too get this right.  The family room is directly above the garage.  The floor assembly between the 2 rooms is 1 3/4 x 9 1/2 lvl’s as joists with 3/4″ Advantech subfloor.  There are no mechanicals running through the assembly.  The rim joist will be insulated with 2″ of Lapolla 4G ccsf.  I was planning doing the same for the bottom-side of the subfloor.  To limit the thermal bridging through the lvl’s, I was going to add 2″ of foil or fiber faced Polyiso covered with 5/8″ sheetrock.  From an air/vapor control viewpoint, I believe I should be fine if I left it at that.  What I am still debating is what to place between the lvl’s.  I am thinking either DP cellulose or Rockwool.  I will have 7 1/2″ of space to fill.  Thoughts?

Root Cellar – In the NE corner of the house, passively ventilated, no subfloor insulation, 4 walls of concrete, below a bedroom with floor assembly of 11 7/8″ TJI’s and 3/4″ Advantech subfloor.  I was planning on insulating this space in a similar manner to the garage, just with more stuffing in the joist bays.

Wine cellar – same floor assembly as the root cellar, but much lower delta T with the conditioned space above.  I am wondering if I can get away with just the ccsf and the Polyiso and avoid any additional insulation in the joist bays?


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  1. user-5574861 | | #1


  2. BrianPontolilo | | #2


    I think that your floor assembly will work fine. Air sealing is the key. Here is a link to an article that may be helpful:

    And when it comes to the cavity insulation, keep one thing in mind, if it sags and pulls away from the underside of the floor sheathing, you will loose performance. So, whatever you choose, be diligent with installation.

  3. user-5574861 | | #3

    Thanks Brian.

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