I love my composite steps because they are not slippery in the winter like wood. But there are necessarily gaps in the composite between the boards so mosquitos and other insects can get in if its used on a porch. So I don't understand the logic of using this for screened porch floors. My dh can attest to the fact that mosquitos go under porches from when he had to do some work under the porch last summer. Dh put some drainage holes/tubes in our existing upstairs screen porch. He can actually close them off with little pieces of chopstick. Helps when we do spring clean up (with mop like indoors.) He has a plan for downstairs too, but not sure exactly what it is. It seems like you could put some thing in for drainage that could be closed up most the time (a hatch comes to mind), Kathy

Bought houses with Pressure treated and cedar decks. Recently changed current deck to IPE. Summary of experience & research: 1) Cedar is soft and subject to mildew. Poor deck choice. Will have short life. Eventually stepping through deck boards convinced me to replace! 2) Pressure treated: The old standard. Cheap to put in, relatively cheap to replace if needed. Vulnerable to carpenter bees(a real problem here). Being porous PT wood, accepts stain well. Can use without stain, but life shorter, greys and develops surface cracks 3) straight plastics. Best spill & stain resistance. No splinters. Get soft in high heat, high expansion/contraction with temperature can lead to sag/wavy. Need joists 12" apart or less to avoid excess sponginess. Minimum maintenance required. Like everything, color fades with sun exposure over time. Unlike wood products, can not renew color by restaining. 4) plastic+sawdust products(e.g.Trex). Stronger and stiffer than straight plastic. Originally claimed low maintenance. After class action lawsuits by deck owners, manufacturers have backed off claim. Mildew eats out sawdust leaving spongy plastic which disintegrates. Most of these products now recommend regular cleaning to prevent mildew growth. Newer versions have external solid plastic wrap to try to prevent mildew. Would not buy until at least 5 year track record of these newer products surviving without mildew or other disintegration problems. 5) IPE. Tough, strong, fire resistant, resist carpenter bees. Difficult to cut, screw(need to predrill and use stainless steel screws) increases installation work. Theoretically, very long life. Can be left unstained (like everything else, sun will turn it grey eventually). In order to keep attractive wood color, regular staining is required. Does not take stain well. Need special tropical hardwood stains. Need to restain more frequently than PT wood. Subject to discoloration by spills/stain if finish wears off or leave unfinished. 6) Other tropical hardwoods. Generally either same as or inferior to IPE in function. Worth considering if want different look than IPE.

We were mulling over the same question a few years ago. We started out thinking screened porch but then realized how much we needed a 4-season gathering space when we entertained. Friends who had gone the 3-season route told us they were essentially 'no season' rooms because they were too hot in the summer and too cold in the winter (you know Minnesota extremes). So we decided to ante up for a 4-season room and we are so glad we did! We went 16'x24', put in 2 sliding glass patio doors to the deck, plus 8 good-sized windows, and a double French door to the dining room. It is a room of light all year round! We followed our furnace guy's recommendation to put in a gas fireplace for heat and a ductless minisplit for air conditioning. They both work splendidly and we can just turn them off and shut the door to the rest of the house when we're not using the room. We love the room in all seasons. With the help and advice of some very skilled siblings, we did almost all the work ourselves and it cost around $40,000.

I'm not trying to waterproof the floor. :). There's no grout in those pedestal systems. The water flows right through to whatever is beneath. I suggested the porcelain as a nice floor for a deck as a non-water proof deck refacing or for above a complete and correct flat roof system, not tiled to the membrane (which I wouldn't even do with schluter), and I recommended the translucent panels as being nice on a second story deck above another to serve to let light through. Rain will blow onto a screen porch. You don't want to trap it. I would definitely have to have solatubes or skylights above to make the translucent panels worth anything. I think some of us are seeing a dry screen porch at the basement level, some are seeing a "wet" screen porch at the basement level (me, first read through--then I wasn't sure), and some of us are seeing a dry screen porch at the upper level (my second guess). And people are recommending flooring either to make the upper level nice or keep the lower level dry. So this whole thread is a mess. I think OP just wants a nice--not waterproof--floor for a second level screen porch which just happens to have a basement beneath.