Hi, newbie here with a perplexing situation. Have an enclosed
(walls/windows) sunroom built over former screened porch. This sunroom
has a wall a/c unit and a space heater, but is not temp-controlled when
not in use. The sunroom rests on a vented concrete foundation, about a 1
- 1.5 feet off the ground.

The builder, however, replaced the wooden deck planks that composed the
screen porch floor. Those planks are the subfloor in the sunroom, and
the planks go under the walls, so I'm not sure about the
wisdom/feasibility of removing them and putting plywood back in their
place.

We only have 1.25 inches from the top of these planks to the bottom of
the swing-in french doors.

Porcelain tile seems to require a little more vertical space than we
have - once you take 0.5" - 0.75" plywood, 0.5" backerboard, then
thinset and tile (5/16") , you're over your 1.25". And a number of our
tile folks seemed rather skeptical and hesistant to even do it with less
thick plywood and backerboard. They seemed suspicious that the planks
underneath are just going to swell with summer humidity and crack the
mortar.

For the 0.5" thick carpet we prefer, it is also too close once you get
the plywood and good rubber padding down. And there'd be no vertical
room under the door for a throw rug for foot-wiping.

Now we're looking at the wood flooring options. My understanding is that
solid wood is unwise, even with a moisture barrier. The choices are then
engineered wood (for its "dimensional stability") and laminates (prob.
with moisture barrier), correct?

HD person says to lay down our leftover roofing felt, then plywood -
screw it down well to the decking planks, then nail down engineered
wood. Does that seem reasonable?

We could also go with a laminate on top of wallboard foam - we have some
of that leftover. In the stores, laminates look OK but feel all wrong. I
understand they're very abrasion resistant and low maintenance, which I
like. I just am not sure they'll look decent. The engineered wood floors
look good but seem unreasonably costly, and they probably have one
refinishing in them at best.

I'd appreciate any recommendations, esp. w/r/t the thickness of plywood
needed over these planks to assure a solid subfloor. Maybe we'd be
better off with two 0.25" thin layers! How about moisture barriers? Is
roofing felt good for that? Seems like that foamboard would be great, as
it insulates as well. Obviously, it is thicker (probably 0.125" or so).

Lastly, what kind of top-flooring would you recommend for this situation
- where the floor should not encounter any water, but will at times
experience temperature extremes and, to the extent the moisture barrier
isn't perfect, some summertime humidity and wintertime dry air as well?

Thanks very much for any advice you can offer,
Russell.