We are adding a three season room. It will not be heated. We want to put wide plank flooring down but have been getting conflicting stories on how it will hold up. People say that the wood will no hold up under the changes in temperature and moisture in Iowa. Can anyone help me with this problem. Any ideas on what will work on the three season room.

A couple of things to think about on the floor in 3 season room. Think about all the fir floors that have been put on outside porches over the last few hundred years and how long they lasted. Also remember that wood is always going to expand and contract with changes in humidity. If it was mine and I wanted wood I'd go for it even of I did get joints showing after time. After haveing spent the last 50 years in the floorcovering business I would still put the wood down if I wanted the look and feel of a natural wood product on the floor.

I built a 3 season porch in Michigan and used 3/4" wolmanized plywood over the joists and then covered the floor with a nice outdoor carpet. Its lasted through 3 winters already with little evidence of wear. And if some snow or rain gets in, I just let it dry. Good luck!

Think outside the box.
Look at Light Weight Colored Textured or Stamped Concrete or equal. (The key here is it is light weight) With proper floor prep. it will be very Durable, it will expand and contract with the climate, and you can change the color or go over it when every you like.

Another choice is ceramic tile. It's easy to keep clean and if you put plants on it, water is not a problem. The drawback with tile or concrete is that it is very cold.
I too, like the idea of wood flooring. If that is what you install, ask the store for info on how to take care of it.