Zero Energy Home Building Features

passive design elements

Used to even-out the highs and lows of cooling and heating while promoting natural ventilation and lighting.

  • Overhanging eaves and window awnings sized to reject high-angle summer sun while receiving low-angle winter sun.
  • Windows sized and placed for maximum cross ventilation as well as "thermo-siphoning," the exhaustion of high hot air and intake of low cool air.
  • Centrally-located stair tower and north-facing skylight reduce reliance on electric lighting.
  • Block walls and concrete slab possess a great deal of mass inside the insulation, storing the interior temperature for later release, smoothing out the daily high and low temperatures.
  • Passively-ventilated garage eliminates the "oven effect" and reduces garage fumes entering the house.

Active Design elements

Roof space features both solar water and photovoltaic collectors.


Systems Engineering

Designed and built as a high-performing home. The building shell, the windows, the HVAC, the hot water, the electrical are designed and constructed recognizing the impacts these systems have on each other and, ultimately, on home performance.

  • Building enclosure - All six sides of the building (the four walls, the roof and the foundation) are designed to manage the flow of liquid water, water vapor, air, and heat (including the transitions from roof to wall and wall to foundation).
    • Roof assembly - Spray foam insulation to manage moisture, air and heat in the roof assembly, particularly at the eave transition to the top of the walls.
    • Roof cladding - "Ultra-cool" metal roof has a high performance coating, giving it relatively high solar reflectance (28%) and emmissivity (85%).
    • Exterior walls - Furred-out cement siding, wood-cement composite block, and non-paper faced gypsum boards provide a moisture-forgiving assembly throughout.
    • High-performance windows - Glazed windows turned to reject and retain heat specific to the Dallas climate (low-e, U = 0.38, SHGC = 0.29).
    • Foundation - A continuous capillary break separates the grade beams and slab foundation from the ground and soil moisture; rigid foam insulation under the secondary cast concrete slab keeps radiant floor heat "in."
  • Mechanical Systems - Each of the following subsystems are integrated with at least one other subsystem.
    • Space cooling ("air conditioning") - In a high-performance building, the space-conditioning equipment can be significantly downsized, resulting in more efficient operation, less mechanical wear-and-tear, and better dehumidification. This 3800 sq. foot home uses a two-stage, 3.5 ton 14 SEER heat pump chills water to cool a forced-air system.
    • Dehumidification - The multi-stage chilled water system allows the system to slow down air flow past the coils and operate at much lower coil temperatures without freeze-up. This means more efficient moisture removal during cooling AND means the system can even dehumidify indoor air during the shoulder season when dehumidification, but not cooling, is needed.
    • Space heating - Water-based heating is drawn from an integrated solar/heat pump/gas-fired hot water tank, and distributed through a hydronic-heating coil in each air handler and through a radiant slab system.
    • High-Performance Duct System - Optimized layout, right-sized and sealed ducts, and ducts kept within the conditioned space ensure high performance.
    • Sealed, Conditioned Attic Space - Eliminates the "oven" found on top of Texas homes and allows the HVAC to be totally enclosed in conditioned space.
    • Mechanical Ventilation - A tight building enclosure requires purposeful and measured introduction of outside air for a high-performance indoor environment. This home has a fresh air duct linked to the central forced-air system that not only introduces outside air, it distributes it throughout the entire home.
    • Solar Hot Water System - A 2-panel, 64 square-foot solar water system is installed on the roof of the south-facing porch. This system is integrated with both domestic water and space heating by way of a highly-insulated, large-capacity hot water storage tank with heat exchanger coils specifically designed for this integration.
    • High Performance Hot Water Distribution System - Most homes feature a substantial waiting period for hot water, as the cooled water in the piping is run down the drain. Here, the optimized layout, correct type and size of pipe, and a recirculation loop reduces the wait time to about 5 seconds for 120° F water. All the cooled water is sent back to the water heater tank.
  • Photovoltaics (PV) - An 8.0 kW (peak) array of PV panels on the south and west roofs of this home supply nearly all of the home's electrical power over the course of a year, at times putting power back on the grid, causing the house meter to runs backwards!
  • Lighting - 90% fluorescent lighting, much of it electronic-ballast high resolution, both indirect and direct, provide soft artificial lighting that saves electricity and helps keep the home cool & comfortable.
  • Water Conservation System - Uses 30% less water for indoor needs and supplies nearly all its own water for outdoor use.
    • Low-flow faucets and showerheads, perform the same as conventional fixtures, but use 35% less water.
    • H-axis clothes washer uses up to 42 percent less energy and up to 59 percent less water compared to standard-efficiency clothes washers.
    • EPA Energy Star dishwasher uses at least 25% less energy and 44% less water than conventional dishwashers.
    • Internet-controlled, irrigation controller reduces outdoor water use by up to 50% while maintaining health and vigor of turf and plants.
    • Native and low-water use vegetation and drought tolerant Zoysia require less water. All planting areas, other than sod, are drip irrigated.
    • An on-site cistern system collects up to 5000 gallons of rainwater for use on the site's xeriscaped vegetation.