Recently I attended the High Performance Green Building: The Future of Affordable Housing conference at UNT.
The conference was excellent and the presenters from Building America and EEBA were particularily good. I have had a lot of exchange with the Building America folks as they are a partner on www.heathershome.info
project with my firm. There is general agreement that insulation in our Texas climate is effective. However, wall insulation is not as effective as you might think.
The most critical issue is shading. Windows on the south and west must be shaded.
Secondly, orientation. If the builidng is sited poorly it will absorb too much solar radiation or too little.
Third is quality of the attic or roof construction.
Fourth is the SEER rating of the HVAC cooling systems, the higher the better.
Fifth would be the amount of glazing or the area of the windows as compared to the area of the floor plan. Too much and your living in a greenhouse that will overheat. Too little and you are living in a cave with the lights on all the time.
Sixth is the quality of the windows. They should be thermally broken with 1" insulated, southern low-e glass.
Seventh would be the insulation in the walls. Typically in our area R 23 is plenty. Too much glass area and the insulation value of the walls is irrelevent.
There are highly regarded professionals in this field who would argue that insulation in the walls in our climate isn't relative. However, the City of Lubbock has proven that ICF constructed homes are about 45% more energy efficient than stick built homes with batt insulated walls. They have a home replacement program for those who qualify financially. Lubbock has built over 150 homes simply using Insulated Concrete Walls and tight construction to achieve this level of performance. What this tells us is that thermal mass can do more to achieve comfort with the least amount of energy expended rather than insulation.