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Q: insulation under hydronic floor staple up

NH Member Posts: 8
Hi, Homeowner here. Location: western Oregon.

My contractor suggested we throw this problem out to others.

I have a retrofit staple up hydronic floor heat system now, only a couple of weeks old. Inside all is well. Outside, after fiberglass batts were installed between joists, leaving the hoped-for 2" air space, we put a layer of Typar to seal it up for the winter. But in no time, condensation had formed and begun moistening the insulation. The Typar was not applied in an air tight way, but even with the slightest air space in the middle of a large expanse, water is condensing.

What about the stated quality of the wrap to allow water vapor to pass? It's obvious that it has to be removed and something else needs to happen.

Please comment and advise. Thanks!


  • NH
    NH Member Posts: 8

    More to add.

    The house is on a steep slope. That is, there is no enclosure around the underside of the house. The space underneath goes from 2 ft to 10 ft. open air. Parked car under there.

    If you have done a house like that, what are some appropriate types of sheathing?

    Is it possible that the Typar should be allowing water vapor to pass and is defective in this particular instance?
  • Weezbo
    Weezbo Member Posts: 6,232
    N H I live on a cold piececof ground*~/:)

    Alaska has Plenty of what one might call; creative, non conforming ,different ,other and somewhat variant construction how ta do it? A. Foam the Rim Joyst and Box beams(blue foam with tremco on all sides will work) B.spray foam that. C push blue foam up into the floor joyst bay,spray foam if you put typar over the stuff it will do justabout zilch for the sandwich,system...Bitchuthane is a water proofing material over foam.It is my belife that to use fiberglass under a post and beam or floating pile building is worse than because it cost money two because it really is a waste of time...your building envelopes vapor barrier is severely compromised you may as well not even bother to install one on the rest of the home creates an in wall in floor a few years you can even grow things in the walls and floorsonce the waters in the insulation it dont "go away" each season it goes thru its cycle un till ...You guessed it... it freezes now whatever insulative value You Thought you had is out the window.the isothene spray foam&foam with tremco make relatively good vapor barriers..and while vapor barriers Facing the weather arent great they certainly have heads over Tyvek i think visquine (Poly ethelyene sheething)on the inside and tyveck on theoutside of walls is ok ...floors, nah, i dont have the same Good Feelings about floors .Typar is a good camoflage material out of the ground and maybe theres alot of it in trailors buh it really doesnt belong on your home anywhere unless its outside in the ground stabilizing the ground.
  • Vermonster_4
    Vermonster_4 Member Posts: 1
    you lost me

    Which Tremco product are you using? Here in VT the most common Tremco product is a two part foundation waterproofing system that consists of a spray-on membrane followed by a foundation board. You must be using something different?

    We have the same condensation problem here in VT. I've been trying to get my hands on a polyiso foam board product from Dow called "Thermax", which is polyiso foam with double sided metalic coating to meet flame spread code requirements in residential construction. The problem with the blue and pink board is that they need to be covered with 1/2 gypsum board or other suitable fire protectant. Not really an option in a 2 foot dirt crawl. Sadly, no-one carries this product and minimum order from the wholesalers is a truckload. Dow, are you listening????

    I think this would be the perfect solution placed into the joist space and foamed into place.

    Maybe you can get it in OR.

  • NH
    NH Member Posts: 8

    Vermonter, is tremco related to typar? Or were you asking Alaska? Anyway, the typar house wrap is what we have, and was suggested because it wouldn't trap water vapor. Turns out otherwise.

    The house was built 30 years ago and had some old R-11 batts and plywood. Didn't seem to have ever been moist. But also, the floor was not ever warm in all that time! So now, warm floor, cold outside and we get condensation....

    When I read about insulation, including Thermax, walls and roofs and foundations are mentioned, but not floors. There must be something about floors I'm not understanding.

    More help needed...
  • Weezbo
    Weezbo Member Posts: 6,232
    Thermax .....

    it is a good product insulation, an Irish buddy and i were some if not the first to use it here many decades ago,our homes had like an r-30+ wall and the homes were as top of the line spec home that could be found any where. as for tremco it is commonly called Black death.Hire a good carpenter and hes used it .... as for the walls being r-11 and everything was fine ...really, i know better than that. if you have no vapor barrier anywhere else then you have many more things going on than met the eye on first go around. Insulation i know insulation.the carpenters savey insulation on our crew or they are outta there:) maybe finding a good insulating contractor or a good carpenter would really help you out the most.and a class in newer building practises would be totally worth your while.
  • NH
    NH Member Posts: 8
    still confused

    Now, I know it's Thanksgiving and all, and I should be doing other things, but the potluck dish is ready for the dinner, which thankfully I am not hosting.

    Here's what sticks in my mind, from Weez: "It is my belife that to use fiberglass under a post and beam or floating pile building is worse than because it cost money two because it really is a waste of time...your building envelopes vapor barrier is severely compromised you may as well not even bother to install one on the rest of the home creates an in wall in floor a few years you can even grow things in the walls and floorsonce the waters in the insulation it dont "go away" each season it goes thru its cycle un till ...You guessed it... it freezes now whatever insulative value You Thought you had is out the window."

    So what I really gotta know is WHY do they use fibergalss batts in the floor if it's useless? What should I be using?

    BTW, W. Oregon is only dry 4 out of 12 months, so humidity is a real factor.
  • jerry scharf_2
    jerry scharf_2 Member Posts: 414
    it isn't cheap

    but I would go with closed cell foam sprayed up into the bays and against the rims. Rip out everything that's there, then just put standard 1/2" ply on the bottom. No moisture will form in or go through the foam. Unless there was a waterproofing problem before, I see no need to include a moisture barrier beyond the foam.

    next best would be polyiso foam baords that are then sealed up with urethane foam from a can. EPS board would work, but to get a reasonable R value it gets thick and R3.5/in.

    The fiberglass insulation is about the worst choice for what you are doing. It's a credit to the power of the fiberglass manufacturers that they have been able to maintain the tests such that fiberglass and EPS have about the same R value per inch. Certainly science has nothing to do with this!

  • NH
    NH Member Posts: 8

    Thanks for your comments, Jerry. I was apparently thinking there would be some science to rely on and some well worn paths.

    Spray up foam seems wrong because I have to leave 2" air space under subfloor where pex pipes are carrying hot water.

    I'm wondering if I have to trash all the fiberglass batts (many dollars!) or might I just let them dry in place after removing the Typar and then board up the whole underside of the house with either plywood or rigid foam board. Then cold air wouldn't contact the bits of airspace left in the joist bays under the batts and make condensation. Opinion?

    Do wish it wasn't winter comin' on.
  • hr
    hr Member Posts: 6,106
    When you say staple up

    is the tube stapled tightly to the subfloor? Or do you have heat transfer plates installed?

    With the transfer plates you get the best transfer, via conduction, and you could foam right up against this system. I have a couple going with isyonene spray foam against the plates.

    Then there is the staple up method with the tube in contact with the floor. The manufactures that promote this method want to see an air space and a reflective surface to take advantage of the tiny conduction contact patch and use the reflective to bounce some radiant energy back against the floor. With this application you might get some of the aluminum sided bubble foil product to staple below, leaving the air gap, then spray foam against the bottom of the bubble foil.

    Or if you have suspended tube, where the tube is held away from the bottom of the subfloor, this depends on conduction (warm air currents) to move the heat from the tube wall to the floor. With this method you need to maintain that air gap. Think I would still use the bubble foil and spray against it.

    I'm not seeing how you will be able to get fiberglass to perform in that application. First off, over an open crawl like that I would think you would want an R-30 or more. you have quite a delta T with possibly 0° temperatures on one side of the batt and 100 or maybe 160° at the tube wall on the top side of the batt (with suspended and some staple up).

    You may have to bite the bullet and start over to get a good insulation detail.

    Perhaps the best part of the spray foams is the incrediable ability to seal off any, and all, gaps. The expanding foams really seek and find the smallest of gaps. Even paper thin gaps between plywood sheets!

    Infiltration will be a BIG number for you if you don't seal up tightly.

    Nothing rips heat from a space like a cold wind. Much more of an energy stealer than just plain "still air" cold. A blower door test, and data spit out, will really open you eyes to infiltration potential!

    Up on piers like that poses some interesting insulation detail. Especially with radiant floor heat.

    You might want be 100% sure about your heatloss calc before you seal 'er up for good. I'd error on the safe side, if it were me, and throw some transfer plates under that baby, at least around the perimeter.

    If it's worth doing, it's worth doing right :)

    hot rod

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  • jerry scharf_2
    jerry scharf_2 Member Posts: 414
    no need for space

    In my opinion, you should trash the fiberglass. It was never a very good insulator and now it's even worse. Sometimes we make mistakes that have $ involved. It's hard, but the only thing to do is move forward.

    What type of transfer plates do you have on your staple up? If it's a good quality one, going with the direct foam will work fine.

    Part of the reason for the air space is that the tubing will expand and contract as the temperature of the water changes. The lower the water temperatures and the slower they change, the less of a problem will exist.

    With the foam and good tranfer plates, the rate at which this happens will be almost purely controlled by the conductive capacity of the floor above, with almost no loss to the outside. This means that the water temperature needed should be a good bit lower and the expansion less of a problem. With cheap or no transfer plates, the ability of the floor to pull the heat out of the tubing will be less, and the water temperatures will need to be too hot and you will get both expansion problems and potentially uncomfortable floors.

    If you're still too concerned or can't do this, go to plan B with the polyiso board and a generous amount of urethane foam sealer.

    My bet that plans A or B would save you quite a bunch of money as well as make your system work better.

    Also, having outdoor reset control on the delivered water temperature will improve things. Lots of ways to add this if it's not part of the original install.

  • rick in Alaska
    rick in Alaska Member Posts: 1,241
    building standards

    I have a guide book that I got at a class on "cold climate building". It has a section in it on insulating under pier foundations where they have fiberglass insulation in the floor joists with rigid insulation under the fiberglass and all of the joints taped or sealed. I believe the main thing is to seal the inside of the structure in order to keep the moisture from getting into the floor cavity from the inside. You can check out there website for more detailed info.

    best of luck! Rick in Alaska
  • NH
    NH Member Posts: 8
    great answer

    Thanks hot rod,
    That was a great answer and I will share your ideas with everyone involved.
    I'll post again when something gets decided.
  • NH
    NH Member Posts: 8
    air space

    Thanks for your answer Jerry,
    The air space is needed because indeed the heating contractor chose to omit transfer plates altogether. He explained it was OK because of the mild climate in Western Oregon. It can get below freezing here but it doesn't last long.
    I did understand that the staples are supposed to be allowing air around the pex pipes, and that was mostly true. In a few places it seemed that the pipes were in contact with the subfloor. Mostly loosely hanging slightly. (Wow -- a sentence of 4 adverbs!)

    Wish me luck. I'll post again when I have news.
  • NH
    NH Member Posts: 8
    seal the inside

    Thanks for your answer too Rick,
    Just to clarify: sealing the inside so moisture does not get into the floor cavity is done how? I doubt there is anything perfectly air tight under my interior flooring materials in this 30 year old, relatively modestly constructed home. Could that be handled by sealing from below under the radiant heating pipes (the 2 inch space)? I'm getting the idea that a sealed barrier at 2 inches, and then insulation with NO air infiltration is the ticket....
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