And, I was examining thermal zone issues ... is there any chance a single pane vinyl window would suffice? I know dual pane is better ... but, is is more than Atlanta needs? Do any major manufacturers like Okna, Soft-Lite, Simonton, etc, even offer single pane vinyl windows?

Why in the world would you ever want single pane windows !!!!!

efficient windows not only keep the cold out, they keep the summer heat out as well. In fact, i would even explore triple pane as an option.

Because there is a tradeoff of cost vs value (thermal, sound, etc) .... Rather than accepting that double pane is the best solution everywhere, the math has to show done breakpoints got double vs single. I certainly believe double is a great sales point!

I grew up in Atlanta, near where your home is. We finished new construction on Lanier about 3 years ago. I would also get a quote from AVI in Atlanta for Marvin Integrity. Very reputable and good to work with. I think it's an easy mistake to 'skimp' on windows. Not saying you're skimping and I fully understand cost/benefits. But windows aren't like appliances, flooring or HVAC that can be updated at a later date. Comfort is a priceless commodity when it's really cold or hot. Even though Atlanta has a temperate climate, we still have a few very cold and very hot days every year that can routinely last for a month or so. Get quality windows and an installation that will last and you will not regret it.

Your local building code will mandate certain performance numbers your new windows will have to meet. Single pane won't meet these numbers.

Good idea on the building code ... will check it out.

I have loaded three photos of the house's (left to right) eat in kitchen to family room (portion shown in middle photo was "captured" from the original sunroom) to the original family room. (there was a sliding glass door to the back yard originally that was removed when the sunroom addition was built ... it was left that way for many years - we reframed with a very large glulam and opened it up ...the exterior walls on the sunroom are stick built with siding).

I need some input regarding options for the sunroom portion of the family room ... as you can see the room has four floor to ceiling windows in the middle that face the back yard, three normal windows on the left side of the room, and two normal size with door to the side of the house on the right.

Given we will be replacing the windows, what are some options that might provide more living space or balance? Ex: we were considering a deck to the left so would remove the window across from the door on the right and replace it with a door that matches the door on the right for balance, and then eliminate the four floor to ceiling windows in lieu of normal windows in order to provide additional space for furniture ... another thought was a a pair of long plate glass windows that don't open.

Would very much appreciate some thoughts on what we could do with such a space.

http://www.houzz.com/ideabooks/58550035

Georgia code says ... "“The 2009 IECC requires that all residential windows have a label displaying the window U-factor and Solar Heat Gain Coefficient (SHGC). Furthermore, all windows must have a U-factor of 0.50 or less and all glazing must not exceed an SHGC of 0.30. These minimum requirements are easily met by using double-paned, low-e windows currently available in the market. Access doors leading to attics and other unconditioned spaces must be weath- erstripped and insulated to R-5, for vertical doors and pull-down stairs, and R-19, for hatches/scuttle hole covers.”

The note re the min requirement being met by double pane doesn't actually require double pane - on the other hand it could be inferring that it is impossible to meet the requirements without it being double pane?

You might want to check here-http://www.dca.state.ga.us/development/constructioncodes/programs/documents/cc/Building_Department_Pilot_Study_GEFA_Release_8-16-12.pdf

It appears Ga has a .35 u factor maximum. If your code mirrors Energy Star guidelines you will need .30 u factor starting 1/1/16. A simple call to the building dept. should answer your questions.

Thanks - U factor jumped quite a bit.