Radiant Heat and Flooring

Q: We’re building a new home and intend to include radiant heated floors, with PEX tubing in concrete below grade, and in gypcrete, as part of a sub-floor, on the main level. Although we haven’t made our final selection, we’re favoring either bamboo or possibly cork engineered tiles. I’ve read that you prefer not to glue tiles down to a radiant heated concrete floor.
Can you please explain. Also, if floating the floor, how are expansion joints handled when there is no molding such as at fireplaces and interfaces between rooms where the floated flooring meets tiles ?
Thanks, John
A: Typically you will want to avoid a glue down application because of the natural properties of any wood flooring. Wood floors will expand due to heat, so since the heat will be directly transferring through your floor it will expand some. Glue down applications will adhere the floor directly to the subfloor and typically allow for very little movement in the flooring. When you have an application that allows little movement, but a heating method which will cause movement, disaster tends to strike. That does not mean that it is impossible to glue down a floor to a radiant heat slab, but its not suggested.
With a floating floor, or any floor for that matter, when you come up to a fireplace typically you will undercut a portion of the brick so that the floor goes under the brick slightly and has an expansion gap hidden away from view. The other matter would be to install some molding like quarter round to cover the expansion gap.
For a transition to a different type of flooring you will always want to use a transition molding. Most transitions now are built with a locking strip which is anchored to the subfloor using screws/nails or a adhesive (such as liquid nail) then the trim itself is simple clicked into place. Based on the height difference of the two floors you can decide which trim to use, typically hard surface to a similar height hard surface involves using a t-mold, though in some cases you may want to use a threshold or end cap/square nose. In the case of floating floors, the trim will still be anchored, but you will allow for a small expansion gap (most of these trims are overlapping) so the floor can properly move without disturbing the transition.