We are considering building a home in the hot humid Fort Worth, TX area. We will be building a 2 story home, with about 3800-4000 sq ft living area. Which type of insulation/energy savings do you recommend? Spray foam? How bout radiant barriers for the roof/exterior walls? Which is proven better? What about costs? Can you use both? Thanks for your input!
You have to look at the entire system when you consider how to best reduce the energy impact of the home you're designing.
Think first about the design of the house; the best way to reduce the "cooling load" on the house is to prevent the heat and humidity from getting into the house in the first place. Take a look at the indigenous architecture of the area - you'll probably find deep overhangs shading windows, lots of porches, light colors, masonry construction, etc. These are all elements of the design that respond to the unique demands of your climate. If you can keep the hot sun out in the first place you'll greatly reduce the need to hold the cool air in with insulation.
How will the house be oriented relative to the sun? Keep windows to a minimum on the South and West sides, and orient the "long axis" of the house East-West. Use natural convection strategies to pull cool air into the house.
"Loose" construction is a big contributor to heat loss/gain. A tightly-constructed house will keep out a lot of heat and humidity.
Decide on insulation types after you've designed the configuration and details of the house to maximize it's response to the climate. You'll find that the need for high-tech, expensive insulation systems is greatly reduced.
Each type/system of insulation has its advantages and drawbacks depending upon where and how it's used. Spray foam, for example, insulates very well but doesn't allow water vapor to pass through - in humid climates it can lead to rot, mold, and other water-related damage. Don't consider systems based soley on their insulation value and cost.
Radiant barriers only work in specific situations; you have to know the design of the house first. Used improperly they can also trap moisture in the house.
In a well-designed energy-efficient house, you might find that good old-fashioned fiberglass batts are more than enough!
Your local energy utility is a good place to start for information about insulation strategies. Most utilities will work with you to calculate your home's energy usage and figure out what type of insulation is appropriate. A design professional in your area might also be a help to you.
Richard Taylor, AIA