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Radiant snowmelt under wood deck

MJS Member Posts: 18
I have a job coming up where the owners want to melt snow from a Trex deck that sits above a flat roof. I was thinking of using Joist Trak aluminum transfer panels attached to the bottom of the Trex decking. Does anyone have any experience or ideas about this type of application?


  • CMadatMe
    CMadatMe Member Posts: 3,086
    Few Questions

    I've never attempted this application. Do have some questions though.

    1. What is the r-value of trex decking?

    2. If attaching plates (which I'm assuming you are going to use). Would you void the deck manufacturers warranty on the deck?

    3. I'm asuming you are going to insulated and close off the underneath of the deck. What happens to the run off of water from the rain, washing the deck and the snowmelt after you close off the ability of water to run off in between the decking itself? Is the deck pitched for run off water?

    4. How is this being controlled? Generally on a snow/ice melt application we are running the system whenever its 32 degrees or below, would you still do this? What would be the response time of the decking? You have less of a mass in this application then with tradiational snow/ice melt, would you need a longer run time in order to melt.

    5. Interested in the results. Keep us posted and best of luck
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • MJS
    MJS Member Posts: 18
    Thanks, good questions

    The builder and the owner think you can put radiant anywhere. (my kind of people!). I am going to check with Trex first and see if they have a problem with applying heat to their material before proceeding to the next step.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Trex have a web site...

    On Trex's web site is an installation manual. I skimmed it and it does not answer all the questions, so it probably makes sense to call them. If the deck is not installed yet, it may give you ideas on how to install the deck. Page 45 is entitled "Physical and Mechanical Properties"

  • EricAune
    EricAune Member Posts: 432
    edited August 2009
    Cost evaluation

    I like the idea, never thought of it before.....but have you sat down with the customer to truly explain the overall cost of the system? 

    Sometimes we are so geared towards "overcoming the challenge" or "pulling it off" that we might forget to consider the customers best interests.  I am not assuming you would do this, rather I am speaking from my own experiences. 

    I would explain the high costs of not only the installation but also the operation.  Let's face it, snow melt is expensive to operate depending on the fuel, overall size and the basic need.  Maybe the customer needs it for liability reasons (restaurant, store front..etc.) but if they just "want it" they should be made aware of this. 

    Consider what Trexx tells you, they most likely will not give you a solid yes or no pertaining to the warranty.  This might leave it up to you and the owner, something I personally would not be comfortable with. Unless you know the owner well enough to speculate they will not come after you if something happens to their deck and Trexx will not help them out. 

    Snow melt systems are tricky...they seem really great, especially to homeowners but if the costs are not known initially they can be the final ingredient to a recipe for poor customer opinion of a contractor.  What I mean is this:  If they don't have an idea that their utility bills are going to skyrocket because of the system, they will get that first bill and most likely shut the system down.  This will ultimately make you look bad because the way they see it is you sold them this system....they do not want to run it....they are out not only the install costs but now they don't even have the $$ to buy a really nice shovel because their bills are too high. 

    Just another viewpoint, hope not to offend. 


    "If you don't like change, your going to like irrelevance even less"
  • MJS
    MJS Member Posts: 18
    Trex snowmelt phase two

    I appreciate the comments and concerns. This customer already has a large snowmelt system and is aware of the costs of operation. This is an addition of a garage apartment with a flat roof that ties into the main house's deck. On top of this flat roof will be a Trex, or similar product, deck which they want to have snowmelt. I have contacted Trex and am waiting for someone to call me back. I will keep the wall updated when info comes in if anyone is interested. 
  • CMadatMe
    CMadatMe Member Posts: 3,086
    I'm interested in the project

    Please keep us up to date.

    I'm still racking my brain on the application of this project and I keep coming up with more questions.

    1.  In a traditional joist trak application the above floor is general a solid interconnected floor. On a deck it is not. How do we come up with centers for this project? The floor boards of the deck are not in contact with each other.  How do we get heat transfer from a floorboard that has a joist trak to one that doesn't? Remember with joist trak the proper installation is to insulate directly to the plate. There is no so called "convection in the oven" (joist bay).

    2. I'm still concerned with how water runs off the deck and what effect water will have on the joist traks over time. Sames goes for the insulation. Once it gets soaked will it inhibit heat transfer.

    3.  I am going to assume that you have to insulate and close in the bottom of that deck in order for joist traks to work. The R-value below has to be higher then the r-value above for this to work.

    4. Since you do not have the same mass as the other snowmelt zones of this project how do you have to have a high temp radiant curve for the deck and a lower temp curve for the higher mass portions of the snowmelt.

    I really belive this can be done. Just working out the roadblocks to overcome in my head. Would love to get yours and anyone elses opinion this project. This is def one that brings out all the stops.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • NRT_Rob
    NRT_Rob Member Posts: 1,013

    your loop lengths would have to be absolutely tiny, since any plate product can only be provided for 1/2" pipe and your typical 125 BTUs/sq ft will drive up your flow rates wildly.

    You might, just might, be able to melt some snow here, but you will not be able to do it on contact because the R-value of the deck will prevent you from moving the necessary amount of energy to the snow. This will be, at best, a "melt over time" situation.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • MJS
    MJS Member Posts: 18
    Thanks for the confirmation

    When the owner and builder first proposed this application I told them they would still have to shovel snow. At best this would keep the Trex dried out after it was cleared of snow. I still don't know how they propose getting enough insulation under the deck to drive the heat up through the Trex. I am meeting with the builder next week. 
  • jhill
    jhill Member Posts: 7

     not sure how you could properly insulate trex decking is going to allow water to pass freely through it. Any snow you manage to melt is going to work against the system.
  • Bucko
    Bucko Member Posts: 11
    Did it - Works -- Not recommended

    I did this on Wood. We used Onix. Two runs per bay. Stapled up R-foil witch is water proof at offers limited isulation factor. If you staple r-foil to decking inbetween the two runs and then on the joist you can provide a sebelance of an sealed air space. It also gives a place for the water to escape. It does melt but the insulasion (poor) needs to be addressed and repaired anually.   They had to have it in a small area next to a suspended slab.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,314
    edited August 2009
    It may work better with trex

    Trex is so dense compared to wood it may work better. I know if it was under wood decking I would say no way as the chemicals leaching from the pressure treated wood would corrode the aluminum in short order. Also the use of snow melt agents would effect the plates. What if they made it a patio with tile or brick surface? Then you could set the snow melt as you would with any other system?

    Check out page 17 of trex installation guide. Heating and bending is possible so loop temps need to be well monitored.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Mitch_4
    Mitch_4 Member Posts: 955
    look at

    Wattsradiant C channel. Unlike extruded plates, the pex clips into place no trap for melted snow, use a A/C tubing insulation on the pex and channel to reduce loss and improve heat transfer.

  • MJS
    MJS Member Posts: 18
    Trying something else

    The builder and I tested some Trex on top of some snowmelt at our shop.

    Heat didn't transfer through the Trex very well and we were able to

    talk the architect out of that idea. They have found another product

    that is like Trex but made with some cement in it also. It has open

    channels in it to run tubing through. The architect and owner really

    want to try and make something like this work. I'll keep you posted.
  • jhill
    jhill Member Posts: 7

     If they are hellbent on doing it and got the money I would install quik traks or another similar above floor system over the joists, cover with 1/8 inch luan, fiberglass and insulate like crazy underneath. Paint the fiberglass black so you don't see it and stay away from anything like the zurn product for this application, its made of mdf plywood definitely don't want it outdoors. Best I got anyhow
This discussion has been closed.