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Insulating and preventing an air gap below Joist Trak

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Marvin007
Marvin007 Member Posts: 52
edited December 2022 in Radiant Heating
Hi, I am insulating below my Joist Trak which is between 2x10 wood joists. See picture. 



***At the moment I need to jump ahead to install a kitchen vent duct, insulate and drywall where my kitchen cabinets will touch the ceiling. They are getting installed in a few weeks. This will happen before I finish the rest of my radiant loops and install the manifold.***

I am insulating for two reasons:
1. To push the heat up through the main floor: 3/4” shiplap + 5/8” for plywood + 1/8” Ditra Mat + 1/4” porcelain tile and thinset.
2. Sound absorption/blocking between basement suite and main floor suite.

I am looking at installing rockwool r22  16” O.C. For 2x6 wood studs. 

Since I have 2x10 studs, how will I force/hold the r22 2x6 rockwool up against the joist trak without it falling down and creating an air gap?

I will be finishing the basement ceiling with 5/8” fire-code drywall.





Comments

  • PC7060
    PC7060 Member Posts: 1,173
    edited December 2022
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    Concur with the use of rockwool. I think it’s actually a benefit to leave a 1”-2” air gap under the plates.  Hopefully someone knowledgeable (@hot_rod)will chime in.  

    I would rip down some 2x to make 3/4” width strips and nail off to the side of joists at the desired height with the 1.5” extending into bay. That will hold in place nicely. Powered finish nailer is key. 


  • RxRoy
    RxRoy Member Posts: 22
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    I used unfaced R19 fiberglass insulation, tight to the plates with no air gap.  I bought a couple rolls of housewrap and cut them down on my bandsaw to a few inches wider than each joist bay.  I stapled cheap wood lath from Menards to the sides of the joists to secure the sides of the wrap and make it look presentable.  You can see in some spots, I had to work above the existing plumbing and ductwork.  I am happy with how it turned out.

    I did the entire 1800 sq ft with this method.  I'm pushing through 3/4" plywood subfloor and 3/4" white oak in most of the house.  Works great!  I havent heated my house with forced air in 5 years (although I do fire it up each year to make sure it still works).  

    Marvin007
  • Dave H_2
    Dave H_2 Member Posts: 556
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    When it comes to Joist Trak, insulation is to be pushed up tight, no air gap. We want the heat transfer to happen via conduction, not convection. Insulation is typically a friction fit meaning that you have 16" oc joists and the insulation is actually wider.
    You could go with paper faced insulation, turn it facing downward an staple it to the joists. Use a jig from the bottom of the joist to know where the staples should go for speed.
    The paper facing direction doesn't matter here because it is between two finished spaces. Usually the paper side faces the living space.

    Dave H.
    Dave H
    PC7060Marvin007kcopp
  • PC7060
    PC7060 Member Posts: 1,173
    edited December 2022
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    Dave’s recommendation of “no air gap /staple up R19” will make the process much simpler. 

    The sound deadening of the fiberglass will not be as good as the Roxol safe and sound  but will help. 

    Marvin007
  • hot_rod
    hot_rod Member Posts: 22,246
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    Insulation support wires are handy, buy them or make your own. Occasionally you come across bays that are wide or narrower then the 14-1/2" spacing.

    Grab some old metal hangers from a thrift store to make custom sizes. Stiff wire, not romex :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    heatheadMarvin007
  • Marvin007
    Marvin007 Member Posts: 52
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    Just to clarify, I can put r22 rockwool insulation right against the joist track and pex. There is no reason to put a foil insulation mat between the two?
    kcopp
  • hot_rod
    hot_rod Member Posts: 22,246
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    No need for any foil, insulate away!
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Marvin007
  • ekubec
    ekubec Member Posts: 12
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    Curious about code, fire, thermal barrier, and air quality.  My basement is unfinished, but I use it as a work shop.  It seems putting faced insulation side down raises fire risk, while having unfaced down exposes fiber glass or rock wool into the  air.  Short of drywalling the ceiling, can anyone recommend a poly membrane which won't be flammable, keeps the fiberglass and rock wool particles out of the air ?  Apologies if this is hijacking the thread, but I just added two layers or R15 faced side up against the radiant, fiber in exposed space.
  • hot_rod
    hot_rod Member Posts: 22,246
    edited January 2023
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    What about a vinyl scrim over the batts. That is how the do metal building insulation around here, it must meet fire code, I see it in all sorts of commercial buildings.
    The cover they used in my shop has some sort of threads in it, more like a rip stop product, stapled to the bottom of thr TJI, 10’ wide rolls is what they used.

    https://www.factorysteeloverstock.com/steel-building-fiberglass-insulation/
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • PC7060
    PC7060 Member Posts: 1,173
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    Install DuPont (formerly Dow) Scoreboard XPS on tbe exterior walls.  It the only XPS foam rated for interior use without an ignition barrier. White cap has the best prices around here. Stick to wall using the Greatstuff Pro red foam can with a gun ($12 can at Lowes / $26 for the gun at Amazon)


  • hot_rod
    hot_rod Member Posts: 22,246
    edited January 2023
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    Ought oh, a combo for a drain on a vertical line? Should be a San. tee
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • PC7060
    PC7060 Member Posts: 1,173
    edited January 2023
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    That’s the remains of a temporary line hooked up during renovations to service temporary kitchen and is 5’ above grade. The line was vented at the sink 20’ away via a studor valve so no risk of sucking a trap dry. The line extending up is a drain servicing a shower and tub above (original and unvented).  

    I left the wye there so I can occasionally hit my head on it when I looking for something on the shelfs immediately below. 

     :p