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Hardwood on radiant slab

hr Member Posts: 6,106
even with a new overpour you need to be sure there is no possibility of water or moisture telegraphing thru.

Does the basement show any signs of previous moisture?

Also at least 30 days for the concrete to cure before installing any wood products. Maybe more if it is a humid basement.

I like the new interlocking floating hardwoods. Check out www.launstein.com. They have some very nice, solid wood, floating floors. Even wide boards. Plus a lot of testing data for the homeowner to view.

hot rod

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  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    Suggested an overpour

    for radiant slab on an existing porch downtown. I would prefer ceramic tile for a floor covering, but homeowner wants hardwood. What are the issues about putting hardwood on a concrete radiant slab??? Thanks for any help. WW

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  • Andrew Hagen
    Andrew Hagen Member Posts: 15
    floating floor

    Junckers talks about it in their floating floor technical information. That Polyfilt is a very thick "rubber" membrane with felt on one side.
  • Ruthe Jubinville_2
    Ruthe Jubinville_2 Member Posts: 674
    neat site

    found it very informative
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    I guess I

    was worried about air spaces between the floor and slab causing a drop in capacity. WW

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  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Wood over concrete

    I have designed several installations of this type using Roth panels. They have a structural foam base with an aluminum transfer plate in on the top surface. This is where the pex would snap in - either 3/4 board using 3/8' Pex or 1' board using 1/2' pex. The foam board minimizes heat transfer to the slab which is most likey uninsulated.

    For real wood floors, you will need to put down sleepers with the boards between to act as nailers. The caveat is, the slab has to be level. You may need to add some flash patch to even the floor out.

    Check out job photos.
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    Thanks for the thread Hot Rod

    There is no moisture issues. The space is a back porch with a concrete floor above a garage. The floating floor would be the ticket I think. WW

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  • old hard wood

    What do you think about a staple-up under a hardwood floor that's 40 years old. I know radiant works well with floating engineered floors, but what about "real" hardwood ? I took a trip to my local flooring whole saler and asked which product they would sell. Their answer was engineered hardwood. They would never recommend radiant for the real macoy. Even with outdoor reset, the flex would warp the floor.
  • ALH_4
    ALH_4 Member Posts: 1,790

    Radiant is used all the time with solid hardwood floors. I have seen it with and without outdoor reset with no problems, though I certianly recommend outdoor reset. I always recommend using extruded aluminum heat transfer plates when installing beneath the subfloor.

    However, I would first get an "OK" from the manufacturer if exotic woods are to be used.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
    Hardwood w Radiant


    Take a close look at your 40 year old floor. I'll bet the planking has gaps in several places - lots of black lines where dirt and grit have settled in.

    The issues with wood flooring and radiant revolves around the moisture content of the wood, both during and after the installation. - These issues can exist whether or not you are using radiant heat. A properly designed/installed radiant system should not create any problems. Through the years, radiant heat with hardwood floors have gotten more than their fair share of bad publicity.

    Regrettfully, there were a lot of contractors out there who thought because they could run baseboard loops, they could install radiant loops. Alot of them did just that, hooked it up to the boiler just like another heating zone.

    It sounds like your wood flooring wholesaler has had several run-ins with improper installations. Instead of learning what caused the problems, and how to correct it, he apparently has chosen the path of never recommending wood for radiant heating - a very short sighted position.

    For most of us in the radiant field, we recognize and understand the problem, know what causes it, and design our systems around it. The change in wood moisture content is what causes the dimensionsal changes. This phenomena exists whether radiant heat is present or not.

    The general accepted limits of heating wood floors are typically expressed by the surface temperature of the finshed floor, usually a maximum of between 82-85F. Depending on who you ask, you'll get different answers. Personally, I don't design over 82.5F. If I need more heat, I look for other methods to provide it.

    For a staple up applications, we are typically trying to force heat energy through 11/4" or more of wood. Excessive heat energy to the plates will bake the moisture out of the underside of the finished wood causing it to shrink and curl under. See the attached graphic 'wood dry shrinkage'.

    Typically, radiant designers will use heatloss programs that will calculate the supply and suface temperatures needed to heat a given room. We design our piping and our control systems to provide it. For me, here on Long Island, radiant heat with hardwood floors is seldom an issue.

    The other type of moisture issue with wood floors would be wet wood expansion - not factor for staple up to an existing wood floor - but I did include that graphic too.

    I've also included an article on wood floor testing done by Laurenstein, a company whose name has bee mentioned many times before here at the wall. They wanted to try and determine when problems really occurred and with what woods. Very informative results. You might want to take a copy of the article to your wood flooring guy - that is if he is willing to approach this subject with an open mind.

    The odds in in your favor, you will be able to use plates in an staple-up type application. Have a competetent designer work up your projetc for you.

  • WOW! Thanks cuz. I saved those files on my computer. I also called the RPA & they told me that a 30% - 60% humidity is whats needed in the winter to help avoid shrinkage. My radiant basics book doesn't go that far in depth about natural hard wood. thanks
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