Converting a porch built on a raised concrete slab to a 3+ season porch. The walls, windows, doors, and skylights are in and are very weather tight. The final piece is the floor. I want to finish with tile and I want to add electric radiant heat under the tile so I can use the room on the occasional winter day. I have about 3" total depth I can use on the flooring. My plan: -6 mil polyethylene vapor barrier bonded to concrete slab -1" polyiso 4'x8' foam boards over -1/2" polyiso 4'x8' foam boards over that, staggered so seams don't line up -3/4" plywood (Plytanium DryPly?) floating over insulation -1/4" Hardee/cement board screwed to plywood -electric heater & tile over that Questions: - do I need plywood? Or can I use cement board directly over the rigid foam? If so, should I use 1/2" thick cement board? If so I have to worry about tile seams lining up with cement board seams, right? - if I use plywood can I get away with 3/8" or 1/2"? Am I any better off with 3/4"? - any better off with DryPly or similar "weather resistant" underlay? - it seems to me that my set-up will pump heat into the plywood, the opposite direction I want the heat to go. Is it worthwhile to add some 1/4" extruded fan-fold type insulation between the plywood and the cement board? Or would this lead to cracking of tiles at the cement board seams? - should each sheet of plywood be free floating on top of the insulation? Or should the plywood be bonded together? i.e. is it better to have 1 bonded plywood subfloor 8' by 8' or have 2 pieces 4' by 8' tied together by the cement board over the top of them? Thanks much for any advice.

Hi, jfcwood. Thanks for the insight. That makes sense especially since the Quiet Walk seems fairly thick. It did occur to me that this might be one of those things that everybody does in spite of the manufacturer's instructions and it works out fine. I can't give these guys the benefit of the doubt though. We are having this flooring installed on two floors of a house that is still under construction. At the time of my original post, the first floor was maybe 50 sq ft from completion and the crew had taken a break for another trade to come in. We saw issues with the expansion gap of the wood and a few other things and brought them up to the installer. He sent us a list of excuses and told his crew to complete the installation ASAP. They even had someone there on 4th of July installing baseboards on any wall with flooring even though that was supposed to be done by another trade. We now have the following list: The underlayment is cut into pieces ranging from about 6"x12" to 2'x4' and laid on the floor in a patchwork pattern that leaves gaps averaging about 1/2" all around. The underlayment touches the wall in some places and is 3" away from the wall in others The overlap edges of the underlayment have been cut off of some (but not all) of the pieces and none of them are taped - despite the underlayment itself being printed with instructions in three languages to tape the edges. Of all of the debris strewn about the house there is not a single roll of tape or empty core. The wood has an uneven expansion gap won't be covered by the baseboards in a couple of places and touches the wall in many places. The wood has been butted up against the exterior doors, wedged into each corner, and touches the lengths of the walls at random intervals. The wood is installed at a skewed angle that is not only unattractive but the narrow taper of the edge pieces is already shifting and allowing neighboring pieces to loosen up. The installer blames the builder for crooked walls but the walls are parallel to about 1/2" over a length of about 20' and the skew is the same at each wall. Each room has one or two prominently placed split or mismatched planks. I am not expecting perfection from mother nature but I am expecting the installer to discard these or use them in less conspicuous places. Thanks for asking - ha ha! I really need advice now on how to handle this without going to court.

Thanks for the replies. In the meantime I've been googling, as I probably should have done before posting this. I hadn't thought about the direction of floor joists, and I'd go with the more structurally sound direction. I tend to agree that Room 3 should go in the same direction as the hall leading into it. I'm less sure about the other rooms. 1 is my office and 2 is a 10x10 guest room dominated by a queen-sized bed. Writersblock, the flooring in the hall changed direction because I asked them to do it that way. I like it and thought it would be better than a run of short boards running crosswise.

Hi @Lynn Morford, I hate to jinx things, but now three months in, I LOVE the floors. I fact, I admire them many times a day (good distraction from current CV craziness). There are about a dozen spots where there were dings or tiny cracks, which freaked me out at first, but I'm pretty sure it was just from the movers. I do take care of them like a newborn child, though--sweep, vacuum, wipe, repeat. Overall, I'm very happy with them! @everdebz, we ended up gluing down. Definitely harder on my body that floating but I've learned to wear slippers or socks and I have yoga mats in most rooms to give my feet a little vacation as I walk through the house, lol. In the end, I trusted @joseph_corlett's comment about letting the contractor make the call on what is best for the situation. Granted, I still pine for the perfect floating feel of my old Junckers flooring, but apparently theirs were unique and most other flooring can't float the same way, so... Anyway, the sad fact is, you can't remove glue-downs without destroying the boards. So fingers crossed you never have to! (I put fake wood in my laundry room and we've already had three floods, so thank god for that decision.)