We enclosed our previously screened-in carport, placing two small conventional windows on the SW side, facing our tiny sideyard. Both the SE side (facing our back garden) and NW side have sliding glass doors, the NW doors having glassed-in miniblinds. Both sliding doors have thermal drapes that can be used to cover them completely in weather that is too hot or too cold, and I have both a portable dehumidifier in the SW corner and and a large "end table" automatic quartz heater in the NW corner. I placed three large area carpets over the concrete slab, giving me essentially three different areas in which to arrange things. The slab absorbs both heat and cold, so if I am attentive to the room's needs it is entirely possible to keep it comfortable year round by adjusting the drapes, ventilating, and running the dehumidifier and heater. My sliding glass doors are screened, so on a good day I can open the doors at both ends and have a wonderful breeze through the entire room, and almost have the look and feel of a sun porch *and* a screened in porch, but without the inconveniences. The NE side opens into our tiny dining area, and we have an air conditioner in there. On very hot, humid days, our "sun room" is cooled sufficiently from that and a ceiling fan we added. This is a fairly low cost solution for anyone with a roofed-over carport or garage that they never park in; it's incredible the amount of living space that can be added to a home--it's now the largest room in the house, and the most attractive in terms of view, lighting, and general comfort.

Thanks for the smart points about rain, klem. And I agree -- there are just so many options, and people are so opinionated about those options, that it's hard to know what to do. My biggest concern remains the weather and how that will affect things, but I know that's a local issue. Maybe I should walk around the neighborhood and survey some people with porches about the sun and the temp, etc. Without adding any new information, my wife and I are divided on what to do -- she thinks just screening it is fine, but I think it would be really nice to have glass for the late fall / winter. If we had to decide today, I think we would either do simple / cheap modern storm windows (which could be opened to the screen on the bottom half during the summer) or do something a bit more adventurous. What I'm thinking on the adventurous front is to screen it in, but do it in a way where there's space to add the old-style wooden storm windows later -- just simple single-pane units that slide into the windo frames and attach with this: http://www.houseofantiquehardware.com/screen-hooks-storm-sash-window-hanger?sc=12&category=91 . The main thing would be attaching the screen on the inside of the frames, or at least creating an outside sill deep enough for the storm windows to nestle within it and still be flush on the outside. Then we could remove the storm windows and store them in the garage during the summer (though that wouldn't help with rainstorms you mention). Does that make any sense? If we did that, we could see how we like the screen in the spring and summer, but add the glass later in an affordable and removable fashion. I haven't seen many people try this, but I think we could build the storm frames and get the glass cut by a local shop. Basically we would recreate something like this company's product: http://chicagogreenwindows.com/storm-window-primer/

Thanks for the eze breeze tip, scrappy. I did some searching and they look like a promising option! Some people complained that the windows had no R value and thus didn't work great for keeping plants through the winter. (All we would do would be herbs, I think.) But it sounds like you and your company were able to stay very comfortable, regardless of the windows' lack of insulation. With the space heater, how long into the winter can you use the room? We've only lived here for a few months, littlebug and lavender_lass, so we're still figuring out traffic patterns. Right now this side door is our main avenue to the car / outside, but that might change to our back door once we redo our kitchen and mudroom. (Thanks again, lavender_lass, for your advice over on the kitchen forums!) I'd want to keep a pathway on this new porch, either way, so the most you could probably do would be a couple chairs OR a sofa and a table for herbs. There's not a ton of space, and I agree that that might mean it's not worth glassing in. I'm still stumped, I guess. Maybe the best option would be to frame the openings, staple on some cheap screens, and add a Habitat Restore screen door -- then we can see how we like it as a screened porch. But we could also frame the windows with the idea that we might add single-pane windows in the future. That way the conversion wouldn't create too much extra work. klem1, I appreciate your suggestions on how to make the glassing in work. I hadn't really thought about shades but you're right -- they could allay a lot of my worries about the summer heat.

You don't want just a space heater. When we bought our house 33 years ago, it had what had been a screened in porch that the owner had put in sliders and turned into a 4 season room. It had a small gas furnace; that got struck by lightning after we'd lived there a few years, and one that size was no longer made, plus the gas line was outside and had corroded and the gas company turned it off. It would have cost nearly $1000 to run a new gas line, even for this short distance. So, we tried the space heater/ceiling fan thing for many years. It was cold in the winter and hot in the summer so we rarely used this nice porch room. After my husband died, I decided I wanted to bring plants in from the terrace for the winter and I needed heat. I found electric baseboard heat, hardwired with a thermostat online and my SIL installed it for me. I quickly discovered that the AC for the first floor of the house (we have a zoned system) did an excellent job of cooling the porch as well, especially with the ceiling fan. I was lucky that there was already a screened porch there and the roof line was an extension of the roof of the house. That saved the previous owner a LOT of money. Last summer, I replaced the cracked plaster ceiling with painted beadboard and it looks terrific. I love this room and enjoy it with all its plants in the dead of winter. In MI, you may want to include a skylight on the roof to bring light into the sunroom and the house. I don't think this will be cheap, even with an existing slab for the foundation. If you do this, be sure to have a plumber install a faucet (like your outdoor ones) so you can easily water plants. We did this years later and what a great idea it has been. In England, one sees conservatories on the back of lots of houses, even modest ones. Unfortunately, in this country they are very pricey.