Luxury vinyl is MUCH much better than it used to be. Go look at some displays if you can. I would either do that or tile it with darker grout.

Thank you; it sounds like that is what you'd recommend, too. I had chosen Earthwerks Terrace Parkhill Tile 12x24 planks, but then started second-guessing myself.

I go with tile. Easy clean with in case of plant mishap. And, in-floor heating with all that glass. My last house had an awesome glassed-in room (Michigan). No plants could thrive, either too cold or too hot.

We have had moisture issues with both vinyl and engineeered hardwood. So whatever you choose make sure they put down a moisture barrier first.

Yes! Moisture barriers will be a must! Thanks.

The other thing that must be added in (for the vinyl) is UV protection against direct sunlight. Traditional vinyl (the stuff at HD or Lowes) has issues with direct sunlight as well as too much heat. It can warp or discolour with too much UV/heat exposure. To get away from these issues, you would normally move to a higher-UV blocking window (75% or higher UV block). But in your situation that would prevent plants from thriving (it could kill many plants simply because the UV coming through isn't enough for their photosynthesis).

If you want this to be sunroom that is filled with plants and with "lots of windows and skylights", then you will need a higher level vinyl. You will need a stable vinyl that is designed for increased UV exposure/heat.

EZ Lay and Drop N Done are two vinyl products out of Korea that are purposefully built to withstand the higher levels of heat...because they are purposefully built for in-floor radiant heat (which is more than 50% of the Korean market).

Please investigate the level of UV block that will be put into the space (most vinyl needs the 75% stuff) as well as do some research into the level of sunlight that will enter the space (I know this will be hard because you do not have it built yet).

If this space already existed, I would tell you to put a thermometer in the direct sunlight (in front of a window) and then check to see how HOT that spot gets. If it gets HOTTER than 85F then you need to look at another material - like stone or tile.

Most vinyl cannot handle heat above 85F. Consistent/long term exposure to temps above 85F can and will warp/discolour the vinyl. The Korean vinyl can withstand temps above 100F (more like 125F). I do not know about their colour stability in direct sunlight. You would have to investigate this yourself.

And to be clear, most "entry level" windows (have roughly 45% UV block) will create heat (pool of sunlight) that will be ABOVE 85F in the summer months. That's why the mid-range UV blocking windows (roughly 75%) are needed for vinyl.

Thank you for writing such a thorough post with so much valuable information. I will be getting Anderson high performance low E-4 Heatlock Energy Star certified windows and doors. Wow, 85 degrees does not seem like much of a heat range for summer! I will do more research. Again, I appreciate all of your help. Barb