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I am covering 1500 sq feet with 3 1/4″ #1 hickory wood flooring. The flooring will go over radiant floor heating set in gypcrete. We installed 2×2 sleepers set on 16″ centers. In many places the sleepers are as much as 1/8″ higher than the gypcrete. In others, the gypcrete is high. Should we put something under the wood? Someone suggested plastic vapor barrier while someone else suggested tarpaper. I have also been told to just nail it down with nothing in between. Also, can I use the really short pieces? I’m not keen in using any adhesives due to vapor toxicity (if that is a term). Any other suggestions will be highly appreciated. The house is in the very dry climate of Colorado. Thank you in advance for your time and expertise.
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David,
I have a favourite hardwood dude that I highly recommend(he respects my tube!) for doing wood over our radiant floor heat projects. He says it doesn't matter whether or not you use red rosin underneath the wood.
A couple of things come to mind:
Glue and screw the 2 x 2's. I don't trust nails alone.
We use 2 x 2's @12" OC with the tubing @ 6" OC. Allows for less stratification and faster response resulting in less water temperature variation which of course is a good thing for wide flooring. I wouldn't recommend glueing anything to gyp-crete. It has a very low shear strength. Actually, the stuff is pure trash IMHO. The Therma-Floor product they have has much more integrity. In your case however, you are only using the gyp as a heat conductor. It performs very well in your application.
If the poured underlayment is in contact with the flooring, you will get better heat conductivity. I'm not sure it would really be worth your while to try and correct the 1/8" gaps. The heat will still radiate to the hardwood, it will just take longer. Also, if there is a good percentage of the floor that is not in contact with the hardwood, your average water temperature will be slightly higher.
Should you decide to correct the situation, you can use a surface bonding agent and any number of bagged self-leveling underlayments to compensate. Who cares if it sticks forever, it will be encapsulated. Just make sure the stuff is cured and do a moisture test before laying the floor.
Do yourself a favour and put this zone on a controller that encourages constant circulation with system reset.
MOST IMPORTANT!!!
Sticker and acclimate your hardwood before installation. Stack the material in the zone where you will use it and set the thermostat or sensor to normal room temperature. If the wood is overly laden with moisture, you may want to ramp the temperature up over several days to prevent the moisture from leaving too fast.
I have personally seen 105F floor temperatures with no ill effects simply because the wood was properly acclimated prior to installation. This was a runaway zone due to someone leaving the zone valves in the 'manual' position.
Scary?? Yes, but it could have been a disaster had the wood not set in the heated structure for a month before it was installed.
The information above comes from a guy whom I trust. He warns me that others may not agree but it has worked for him. So far we have had ZERO problems(knock on wood) even with the wide boards.
Good luck on your new abode and take the time to do it right.
Jeff
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I am covering 1500 sq feet with 3 1/4" #1 hickory wood flooring. The flooring will go over radiant floor heating set in gypcrete. We installed 2x2 sleepers set on 16" centers. In many places the sleepers are as much as 1/8" higher than the gypcrete. In others, the gypcrete is high. Should we put something under the wood? Someone suggested plastic vapor barrier while someone else suggested tarpaper. I have also been told to just nail it down with nothing in between. Also, can I use the really short pieces? I'm not keen in using any adhesives due to vapor toxicity (if that is a term). Any other suggestions will be highly appreciated. The house is in the very dry climate of Colorado. Thank you in advance for your time and expertise.