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Staple Up with Cantilever

boulderz
boulderz Member Posts: 33
in Radiant Heating

I am planning a staple up installation in a newly constructed small addition. The area is 14’ x 20’ (kitchen) with conditioned space below (12’ x 18’). There are 2’ overhang/cantilevers on 2 sides. The spray foam guy is planning 4.5” closed cell foam in the overhang areas. My question is on the radiant. Can the loops be extended below the cantilevered areas? Construction would be radiant tubing in aluminum plates, air gap, reflective, then 4.5” of foam? If this is a bad idea, any other guidance? Thanks

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 18,598

    Not a radiant expert others will comment but I would say it would be ok

  • hot_rod
    hot_rod Member Posts: 25,705

    no need for reflective foil if you use transfer plates , or the air space for that matter

    You as much batt as the joist depth allows

    Spray foam the rim joist to eliminate infiltration

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    kcopp
  • mattmia2
    mattmia2 Member Posts: 14,239
    edited September 28

    JJust make sure it gets insulated and especially air sealed well and there aren't any voids enclosed during framing that get missed. My concern would be it would be easy for it to freeze if that isn't done.

    Maybe home run it separately to the manifold in case something goes awry so you can isolate it.

  • Kaos
    Kaos Member Posts: 736

    People overestimate how much reflective barrier does. It is only about the equivalent to R2 of insulation (basically squat) so in most cases it is not worth the effort.

    Make sure the installer carries the spray foam up the rim joist along the overhang and back down to the foundation. People often think stuffing batt insulation into places air seals, but this does nothing except filter the air leaks. You need something solid (spray foam or rigid insulation with canned foam) to air seal properly.

    Make sure to fill the rest of the cavity with fluffy. There is nothing magical about spray foam. That 4.5" of ccSPF is about R25 long term (when installed it is higher, but looses R value over time), which is not a lot for an exposed floor like this.

    What is the plan for the rest of the insulation? Generally with crawl you want to insulate the stem walls not under the rest of the floor. With heated floors you do want some R value under the floors though to limit the amount of heat going down, this can be pretty much anything. The cheapest batts you can stuff up TIGHT against the heat plate work great.

  • boulderz
    boulderz Member Posts: 33

    To better describe, this is a 2 story addition to existing house. The lower level (bedroom) is on a slab and there is radiant installed in the slab. Under the slab is 4” XPS. Exterior walls have zip sheathing with R6 foam. The upper level is a kitchen. I had planned to do quiktrak above the subfloor with radiant but contractor messed up floor height so it doesn’t match existing house floor - so now doing staple up to make it work. The second floor in the kitchen cantilevers on 2 sides 2’ out. This is the area I’m concerned about. Seems like what I’m hearing is install the radiant but keep it back from the exterior wall to allow spray foam between the piping and exterior. Then Insulate under.

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