Use energy modeling to optimize insulation, air sealing, and equipment selection.
Orient the house with the long axis east-west to minimize exposure to rising and setting sunlight. Design living spaces to face cooler facades. Place patios and decks on the north side in the shade of the building.
Concrete, brick, tile and thick plaster will absorb large quantities of heat and release it slowly. This “thermal mass effect” helps even out daily temperature swings. In hot climates, heat is absorbed during the day and released at night when outdoor temperatures are lower. Thermal mass is most effective in desert climates that experience large temperature swings from day to night. Heat is absorbed by these high-mass materials during the daytime and, if nights are cool enough, opening the home at night can help vent the heat outside.
Floor and wall insulation can be reduced in warmer climates. For wall insulation, though rigid foam board rated at R-10 could be sufficient, in some cases, optimum insulation levels are best determined with an energy model. If the walls are concrete-block, rigid foam should be installed on the exterior. A slab foundation should not have insulation below the slab, as omitting it will reduce the home’s cooling load. Slab perimeter insulation is recommended where termites can be controlled. Where termites are a problem, consider rockwool boards, such as Roxul Comfortboard, which can be used below grade and will deter insects. Ceramic tile floors are best for flooring as they will help transfer cool, while carpeting should be avoided. Ceilings or roofs should be insulated to at least R-30 depending on energy modeling.
Use highly reflective roofing. White metal roofing or white concrete tile roofing is preferable. If the house has an unconditioned attic, radiant barrier roof sheathing is recommended.
Select the building site for natural shade or design landscaping to create it.
Every window should be shaded, whether with natural shading, by window overhangs of 3’ or more, by being recessed in thick walls, by wide porches on the east and west, or by using a combination of these techniques.
The majority of windows should face north or south. Windows on the east and west should be minimized because they are more exposed to low angles of the sun and lead to overheating more than windows on the north or south.
Energy efficient windows are important. A solar heat-gain coefficient (SHGC) below 0.25, and preferably as low as 0.20, should be specified.
Carefully seal the home’s thermal envelope because air sealing is just as important in warmer climates as it is in cold climates. In warmer climates air leaks increase the home’s cooling load and allow humidity to enter the conditioned space, so air conditioners have to work harder. In humid climates, airborne water vapor from outdoors presents a threat of mold and rot that will be reduced by air sealing.
It is very important that the home’s cooling and ventilation ducts are inside the conditioned space and duct joints are carefully sealed. If ducts can’t be placed within the living space, locate them inside air-tight insulated chases, inside soffits or in a sealed and insulated attic.
Warmer climates are well-suited to heat pump water heaters. They should be placed in a buffered space, such as a garage, where they would cool and dehumidify the space while heating water.
Since moisture makes a home feel hotter and makes air conditioning more expensive, the following strategies should be used to prevent it entering the home: wrap the house with an effective moisture barrier including proper flashing; make the home as airtight as possible to keep moisture out; and install a properly sized energy recovery ventilation (ERV) system with vents in the bathrooms, laundry and kitchen to expel moisture, while retaining the home’s cool air. Take care to properly size the central air conditioning system, as an oversized system will not effectively remove water vapor. For very humid climates consider installing a dehumidifying heat pipe in conjunction with the air conditioner. Another option is a supply ventilation system with integrated dehumidifier.
Internal Heat Gains
Waste heat from lights and appliances are especially harmful to the performance of hot-climate houses in summer. Use LED lighting and select the most energy efficient appliances available, including energy efficient electronics, to minimize heat gains. Many of these concepts are detailed by Martin Holladay of Green Building Advisor.