Hot and Humid Climate Zone

This map shows the Hot & Humid Climate Zones of the United States. This zone covers eastern Texas through Florida and reaches up to mid-Georgia; it also includes Puerto Rico and Hawaii.

Hot and humid climates present several challenges for home building.

The intense solar radiation in such climates imposes a large thermal load on houses that can increase cooling costs, affect comfort, and damage home furnishings. This section includes some of the best methods to minimize the impact of solar radiation on the building, its mechanical system, and its occupants.
Moisture in the form of high humidity and high rainfall is another significant problem. Most of the hot and humid climate zone receives more than 40 inches of annual precipitation. Some areas get more than 60 inches of annual precipitation. The ambient air has significant levels of moisture most of the year. Because air-conditioning is installed in most new homes, cold surfaces are present where condensation can occur. Controlling the infiltration of this moisture-laden air into the building envelope and keeping moisture away from cold surfaces are major goals of design and construction in this climate zone.

Hot and Humid Climate Best Practices

Housing types vary greatly throughout the different climate zones, but nowhere is the contrast as great as in the hot-humid climate of the southern United States. In many parts of Florida, block wall assemblies predominate, whereas wood frame is most common in Texas.

In the face of this diversity, no single set of measures will achieve the 30 percent energy savings in space conditioning and water heating that qualifies a home as ENERGY STAR^®-qualified. The principles included in these best practices need to be adjusted for different circumstances. A building scientist, such as a home energy rating professional, can help homeowners determine which combination of best practices is most appropriate.

These best practices are derived from Building America's research on tens of thousands of homes. Building scientists have tried and tested these measures on actual homes in the field. While not every measure will be right for a specific home, achieving high-efficiency performance and a healthy indoor environment depends on making informed decisions about interactions among all aspects of the building system.

Special Considerations for the Hot and Humid Climate

Site Design

In the hot and humid climate zone, planners should do all they can to avoid the entry of solar energy into houses, especially in summer. Site planners have two important tools to help avoid solar heat gain: lot orientation and shade trees.

Lot Orientation

When the house has clear single glazing, which is not recommended, interior shades, overhangs, and various combinations of shading devices significantly reduce energy costs. Naturally, a completely shaded house has the best performance in a hot climate.

Foundations

Slab foundations are more cost effective and prevalent in new construction in the hot and humid climate zone than other foundation systems. Building foundations should be designed and constructed to prevent the entry of moisture and other soil gases such as radon.

Slabs and Basement Floors

Where gravel is scarce, such as in Florida, builders often pour slabs onto sand. When sand or other native fill is used, a three- or four-inch perforated and corrugated pipe loop can be used for both drainage and radon control. Drainage matting also may be installed over sand.

Slabs in hot and humid climates are generally not insulated, even at the perimeter, because of the low overall heating load and code restrictions on below-grade use of rigid foam insulation.

Walls

Wood Frame Walls

Best practice for frame wall construction involves advanced framing techniques. However, more traditional wall construction techniques can also achieve 30 percent space conditioning energy savings in the hot and humid climate zone. More information on gaining greater efficiency using advanced framing can be found at the Building Science Corporation's Web site. If advanced framing is to be used, a detailed plan should be developed showing framing placement.

External walls with 2 x 4 framing may achieve 30 percent energy space conditioning savings in the hot and humid climate zone and should include the following features:

Exterior finish such as stucco over paper backed with lath (paper to have perm rating of <1 perm), vinyl siding, or cementitious board.
A housewrap installed as an air and water barrier.
R-13 (high-density) friction-fit unfaced fiberglass insulation or blown-in cellulose insulation.
R-13 friction-fit, unfaced batt insulation on frame walls between the garage and the conditioned space, including bonus rooms.
Rim joists that have unfaced R-13 friction-fit batt insulation cut to fit.
Foam-sealed or caulked top -plate and exterior wall penetrations.
Sealed gypsum board to control air leakage through the walls, especially in penetrations to garages and porches, and where the walls meet the ceiling.

Masonry Walls

Masonry walls are common in parts of the hot and humid environment, especially southern Florida. Masonry walls may be finished with stucco, wood, or other claddings. Best practices to improve thermal efficiency include the following:

Install unfaced, semi-vapor permeable rigid insulation on the interior of wall assemblies. Avoid foil facing and polypropylene skins.
Install wood furring over rigid insulation. The rigid insulation should be continuous over the surface of the wall, except for a 2 x 4 furring strip at the intersection with the ceiling. This blocking attaches directly to the masonry block and serves as a draft and fire stop. The rigid insulation abuts the blocking but does not cover it or extend behind it.
Surface-mount electrical boxes to the masonry, avoiding chipping or chiseling. The rigid insulation, furring, and gypsum board will build up around the box for a flush finish.
Use pressure treated lumber to frame out sub-jambs and spacers within window and door rough openings.
As with other walls, foam seal or caulk penetrations to the exterior or through top and bottom plates.
In addition to sealing all penetrations, control air leakage through the walls by sealing the gypsum board. Pay particular attention to air sealing penetrations to garages and porches, and where the walls meet the ceiling.
When pouring the slab, create a seat in the concrete to accept the block and seats in the concrete to act as drain pans where exterior doors and sliding doors will be located.

Concrete Walls

Some builders in the hot and humid climate zone are beginning to use poured concrete walls for residential construction. More information on this approach is available in Builder System Performance Package Targeting 30%-40% Savings in Space Conditioning Energy Use (PDF 6 MB) prepared by the California Air Resources Board (CARB, 2004). Download Adobe Reader.

Insulation

Reflective Insulation Systems

Reflective insulation systems are effective in the hot and humid climate at reducing peak cooling loads, especially if ductwork or cooling equipment is located in the attic. For information about reflective insulation systems, visit the insulation Web site.

HVAC

Heat pumps

Heat pumps are preferable to electric resistance heating in all but the warmest of climates, such as in southern Florida, where there are fewer than 500 annual heating degree days. A unit with a HSPF of 7.7 or more will reduce the electric consumption during heating by more than 50 percent relative to electric resistance heating. The new standard will require that central heat pumps have a minimum rating of 7.7 HSPF. Lists of all ENERGY STAR-rated appliances can be found at the ENERGY STAR Web site.

Supplemental Dehumidification

Supplemental dehumidification is an important component for homes in the hot and humid climate zone.

Building America recommends that houses be equipped with a dehumidification system or designed so that a dehumidifier can be easily added. One Building America team recommends that all homes in the hot and humid climate zone have supplemental dehumidification. Other teams call for these systems in homes where moisture proves to be a problem. Supplemental dehumidification may be required in energy-efficient homes, where air conditioners tend to run less often, or in homes where oversized air conditioners lead to short cycling.

Building America scientists field tested six dehumidification systems in Houston. The study identified a good supplemental dehumidification system with reasonable costs and performance. The system can be installed either during construction or after occupancy. The best performing system from the Houston study consists of the following:

Stand-alone dehumidifier located in the attic in an insulated enclosure (if the attic is not conditioned) and ducted to the living space,
Dehumidistat located in the living space,
Fan cycler and an integrated supply of fresh air (see the section on ventilation) because moisture control performance is dependent on effective and regular mixing of indoor air.

Other systems may work well in circumstances where allergy-sensitive homeowners are seeking high-performance air filtration. In all homes, spot ventilation in kitchens and bath rooms is critical to humidity control.

ENERGY STAR qualifies the energy efficiency of dehumidifiers in terms of liters of water removed per kilowatt-hour of energy consumed. To earn the ENERGY STAR label, dehumidifiers must fall within the range of greater than or equal to 1.20 to 1.50 L/kWh for standard capacity units. The requirement for high-capacity units is greater than or equal to 2.25 L/kWh. Lists of all ENERGY STAR-rated appliances can be found at the ENERGY STAR Web site.