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Radiant floor Staple-up insulation

andrewandrew Member Posts: 11
I understand that a staple up application should be insulated and that an air gap of 2 inches should be left between the floor and the reflective surface of the insulation. The easiest way I see is to staple the insulation to the underside of the TJI web. This would give 1 and 3/8 inch air gap. Will this work?
Also do you have to seal each end of the insulation up to the floor or do you leave this open to creat air flow?


  • Ruthe  JubinvilleRuthe Jubinville Member Posts: 67
    staple up

    Yes to both questions.
  • andrewandrew Member Posts: 11
    How much

    Thanks Jerry. Now the question is how much insulation? My installers are not all that fond of fiberglass and I'm lookin at Reflectix which is bubblewrap sandwiched between two layers of aluminum. I believe it is mainly for duct wrapping with an R value when tight wrapped of 6.The manufacturer says it's R value is considerably more if installed with an air gap. I have installed radiant in slab in the basement, the house is very tight although the builder builds 2x4 walls with R13. The attic is R38. I'm thinking this Reflectix will do the job. Any thoughts any one?
  • hrhr Member Posts: 6,106
    In all honesty

    the foil get dusty and dirty, somehow, and offers little reflective value, in my opinion.

    I visited a staple up job that was insulated with foil faced batts. This was built by an insulation contractor. I had to pull down a bunch of insulation to troubleshoot an under heating area. I was amazed how much dust was on the foil. Between the printing and the dust layer... why bother.

    I'd say R19 batts would be the best bang for the money. It's an honest R-19 is installed properly (not compressed). If you go with a bubble foil, I would still suggest R-11 below it. Not a lot of trapped air in a 1/2"ir bubble :)

    When you say staple up, are the tubes stapled tightly to the subfloor or are they hanging below. With a true staple up there is some conduction transfer, which is a plus.

    hot rod

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  • Dave MeersDave Meers Member Posts: 103
    Staple-Up Insulation

    I am currently installing 1/2 inch Wirsbo Pex with oxy barrier using staple-up method between 12 inch deep TJI's spaced on 16 inch centers. I am using omega style plates with the groove offset to allow for the Pex to be installed on 8 inch centers between the TJI's. There is only about a 1/2 inch of subflooring exposed between the plates. I was planning on stapling 1/2 inch foil faced urethane sheathing between the TJI webs so there will be a 1 1/2 inch air space below the plates. I think the urethane is rated about R-7. I then plan to install 10 inch thick fiberglass batts below the urethane between the TJI's. This should provide about an R-35 or so below the plates and tubes. Would you consider this overkill and a waste of money or will I gain any BTU transfer to the floor above. The subfloor, by the way is 3/4 inch Advantec with 3/4 inch thick strip hardwood flooring. By the way, this is the best heating info site on the web. Thanks!
  • Mark EathertonMark Eatherton Member Posts: 2,542
    Don't bother...

    Your system is based primarily on conduction heat transfer. Just use unfaced R-19 insulation pushed up so it just contacts the heat transmission plates. No gaps. no "relective" foil. Just good ol' dead air.

  • Mark HuntMark Hunt Member Posts: 4,909
    Dead air

    Fiberglass insulation sucks when it comes to halting air movement and if air moves through it the R-value drops like a rock.

    I would use the Reflectix and make sure you seal it at both ends of the joist bays, then run batt insulation under it.

    If nothing else, the reflectix will act as an air barrier. You should also be sure to seal ANY AND ALL penetrations into the joist cavities. Little thing called stack effect.


    Mark H

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  • hrhr Member Posts: 6,106
    Mark H

    if the choice were JUST Refletix or just R-19 batts, I think my money would be on the R-19 batts. Going with kraft faced batts would accomplish your goal, for not much added cost.

    I've been on a number of bubble foil under tube jobs and it sure feels warm under that thin insulation. I'll buy the reflective value, to a point, if you keep it dust free :) But it's the amount of trapped air that provide the true stop. Isn't it?

    Seems the R-value claims have notched down a bit since the bubble products first hit the market.

    Otherwise, seems those foil products would be used in exterior walls for insulation. Would you insulate your home's exterior walls with just bubble foil? It's the same heat flow that we are trying to slow.

    hot rod

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  • Dave MeersDave Meers Member Posts: 103
    Staple-Up Insulation

    Thanks for the feedback. I guess what I'm really trying to determine is if an air gap with a reflective foil will improve the heat tranfer up through the floor. I definitely will be installing at least 10 inch thick fiberglass batting below the plates which will exceed the R-19 by quite a bit. I understand that an air gap with the relective foil is required if you don't use plates. Since I am using plates and they almost cover the entire exposed subfloor between the TJI's, will an air gap with reflective foil improve the conduction up through the floor? I'm not yet sold on the reflective bubble wrap, certainly not used if by itself. It seems that they're are a lot of differing opinions on this topic. Thanks!
  • Wayco WayneWayco Wayne Member Posts: 2,470
    If you are using

    extruded plates it seems to me the refective foil bubble wrap would be unecessary in addition to the Batts. WW

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  • Mark EathertonMark Eatherton Member Posts: 2,542

    Thermal energy is transferred in one of three ways, or all three depending on the type of install. In the case of suspended tube, it uses radiant, conductive (thru the walls of the tube) and convective. In your case, you are dealing with conductive, which is the most efficient method. If you leave an air gap, it will cause the other two lesser efficient methods to kick in, and you don't want or need it. Stick with conductive.

    In the case of true staple up, the conductive portion is limited by the amount of tube to floor surface contact, which in most cases (excluding distorted rubber hose) is minimal at best.

    I have had cases of staple up where the insulation was pushed up tight against the tube and it wouldn't produce enough heat to keep the dwelling warm. I sent in a crew and had them creat a uniform air gap below the tube and VIOLA, warm home syndrome. We even turned the operating temperature down on the tube.

  • Mark EathertonMark Eatherton Member Posts: 2,542
    I agree with HR....

    In fact, I've tested it under controlled circumstances and found it to have an actual R value of around 1, which could be 100 times better than 0, but...

    Spectral reflectivity is important when talking about a materials reflective capability. I have yet to find ANY below the floor application that DIDN'T have a substantial build up of dust after even a short period of time. Take a horizontal mirror and throw baby powder on it and then shine a flash light on it to see what the affect dust has on spectral reflectivity.

    On the previoulsy referenced staple up problem job, the backing on the insulation was kraft paper, not foil. Just the addition of the air gap alone made ALL the difference in the world.

  • Mark WolffMark Wolff Member Posts: 256
    Less Hot/Cold

    You also get less noticable hot/cold strips on your floor. Especially with your hardwood.

    Keep the 1 1/2"-2" air gap. Use the board and your batt insulation and you will be fine. You need to focus though on stopping any air transfer as previously stated on this thread. The air movement will kill your insulation value.
  • Wayco WayneWayco Wayne Member Posts: 2,470

    Am I missing somthing? You give all of the different ins methods but I don't see the results. It could be me. I have been working a lot of overtime. I have customers who are watching this thread with great interest since they have a suspended tubing floor,* with just reflective bubble wrap stapled to the bottom of the tgi. Not the full 2 inches I'm afraid and no batts under the reflectex. *-(not installed by moi)

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  • Mark EathertonMark Eatherton Member Posts: 2,542

    Forgot to include the final results slide...

  • andrewandrew Member Posts: 11
    insulation redux

    Well I really opened a can when I posed the original question! Now here are two more! I've already installed the tube. 1/2 inch pex 8 inch on center with aluminum plates holding the pex tight against the floor (3/4 inch T&G particle board) I have installed reflectix along the bottom of the topplate of the TGI giving me a 1.5 inch air gap and have stapled the insulation tight at each end of each bay.
    Question 1
    Do I still have to install fiberglass? If so, since this is in the second floor ceiling, would not fiberglass vertically across the end of each TGI bay creat an air gap under the reflectix and the sheet rock thus eliminating the need for the fiberglass to run the entire lenght of each bay?
    Question 2
    Slightly off the subject. Literally the last staple shot by a tired operator put a staple into my PEX. I can and probably will require him to rip out the insulation, aluminum plates and the 300 foot loop and replace same at his expense. However that seems somewhat draconian if there is a guaranteed method of repair. It is near the end of the loop and we could slip stuff over the PEX to get to the failure point. I'm not going to cut and put in a bayonet connection but wonder if there is an external patch to repair this problem?
  • mphmph Member Posts: 77

    I don't know of any kind of external repair. Rehau has a bullet-proof fitting system that I don't hesitate to bury in a ceiling or floor.

  • Mark HuntMark Hunt Member Posts: 4,909
    Tough call

    I agree HR, that once the foil is covered the reflective value is gone.

    My problem with the kraft faced stuff is that mold loves it.

    I guess my point was that fiberglass is not an air barrier and you can lose a TON of BTU's through convective loss.

    Holes made by electricians, plumbers, etc. should be sealed. Enough of them in a joist space and you could have a real problem.

    The bubble foil is a heck of alot easier to work with, but I agree that the cost may not be justified.

    I try to get an air-tight seal, and kraft faced fibergalss does not lend itself to such. I suppose you could tape the seams and joints though.

    I've thought about this quite a bit. I am curious if any tests have determined how long it will take for the reflective value to be negated. Will dust completely cover the facing? Or will it be concentrated on a percentage of that area?

    BTW, fiberglass manufacturers have cheapened their product in the past few years, but standards have not changed. A 6" batt of insulation today is still listed with the same R-value as a 6" batt from ten years ago even though the new batt is not remotely the same.

    I am not an insulation expert, I got those details from someone that is.

    Stop air movement outside the joist space. However you can.

    Mark H

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  • DuncanDuncan Member Posts: 33
    Please Andrew, have a heart!

    Let them cut it and splice the leak, it's common practice and it's no big deal. Be reasonable, man!

    As for insulation, the more the better, within reason. Yes, install the fiberglass under the reflectix. Fiberglass is cheap and effective. It also has some value as sound insulation if nothing else. If I recall correctly, insulation installers charge about $0.05 per square foot to install the stuff. Peanuts.

    You definitely want to carefully stuff the ends of each bay with fiberglass if they are outside walls! Gotta insulate outside walls!

    I've watched this thread with interest regarding the various opinions on insulation. Most of them correct, incidentally. Have you asked the manufacturer what their recomendation for insulation is?

    What kind of plates are we talking about here? Thin flashing metal or thick extruded plates?
  • Uni RUni R Member Posts: 663
    Insulation Test

    Mark, if I had known you were going to do a test like that I would have Fed-Ex'd you some rockwool insulation to include in the test. Some R23 Roxul 6" batts with a Tyvek house wrap air barrier stapled across any open joist bottoms seems like an ideal candidate for comparison. It would stop airflow out of the joist space while not trapping condensation and also be using a better insulation material than fibreglass (IMHO).

    When is round #2?
  • devoedevoe Member Posts: 1
    Should I have completely stapled the PEX ?

    Old maple floor 3'4" with 3/4" subfloor 85years old. I pexed under it in the basement ceiling. Nice warm basement. No insulation under the pex. Just letting it radiate up through the floor. Is that OK? I have completely stapled the pex to the underlayment in the basement ceiling? Is this conductive application appropriate for a 3/4" underlayment 3/4" maple flooring.

    OR should I have let it hang off the ceiling of the basement ( the bottom of the underlayment) for air flow? OR is it better to staple it tight to the subfloor. My floor is creaking like crazy when it heats up. Is that the pex or the wood sounds like the wood but I feel its the pex because it is consistently creaking. Not like an old floor that kinda creaks here and there. Should remove most staples except maybe on the end turns and let it hang on the joist braces?
  • NRT_RobNRT_Rob Member Posts: 1,009
    several issues

    suspended tube is better than staple up.

    airspace is needed for either one if you aren't using plates

    all radiant requires insulation underneath.

    and, to build on the old thread you've bumped, reflective insulation stinks long term, use stuff with real R-value.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
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