Case Study: Johnson/Chronister Residence
Images Of...

Project Goals
The Johnson/Chronister residence was designed to be sustainable and environmentally responsive. The plumbing fixtures are water conserving, and overall water consumption is greatly reduced by the spray irrigation septic system. Many recycled and local materials were used, along with a soy-based total fill insulation at the roof deck, and a 14.0 SEER heat pump.

The highly sloped terrain provided quite a challenging site for this new home. The view, the terrain, and the trees are all accounted for in a very site-specific and unique design that is flexible enough for future growth. The concept of the home is that of an old English Manor that has been added onto over time. The timeless architecture adds comfort and warmth to an already spectacular site. To complement the old world architecture, antique and salvaged materials are abundant, showcased by hundred year old french doors and stained glass windows, and antique door knobs and plates.

Project Name/Location	Rating	Completion Date	Cost/ft2 (excludes land)
Johnson/Chronister Residence Old Westlake in West Austin	5-Star	December 2005	not available

Project Description
The first floor walls of this residence are cast earth, a process similar to rammed earth, but not as labor intensive. Cast earth is a structural material made with earth and calcined gypsum. Cast earth can replace wood or steel framing in residential and light commercial buildings. The cast earth mixture is poured in place using forms, similar to concrete, and takes very little time to harden. Cast earth does not shrink as it dries, so when the forms are removed, the walls are extremely strong and do not crack as easily as a rammed earth or adobe. The Johnson/Chronister residence is one of two cast earth homes in Austin. Architect Images Of... also designed the Cope Residence in Austin as a cast earth home.

The Thermal Chimney
This home features a passive solar technique called a cupola, which functions as a thermal chimney. The cupola, or thermal chimney, is based on an ancient concept of air movement that man has utilized for hundreds of years. The idea is very simple, at the highest point of the house, build a "chimney" that allows hot air to rise (which it does naturally) out of the house. Hot air escapes through the operable windows in the chimney, and cooler air is drawn into the home from the lower portions of the house and ground, by natural convection. Other passive solar concepts that work well in a hot/humid climate include proper orientation, building overhangs, and daylighting. During a hot summer, one thing we need to be comfortable is a lot air movement over our skin. Good natural ventilation is especially critical if you want to limit the use of air conditioning. However, in the hottest part of the year, breezes can be slow and humidity can be very high. This is why it is important to create good natural ventilation on at least two sides of a room, preferably opposite sides, which allows air to flow in and out rapidly.

Project Features

Energy:

• Operable thermal chimney
• 150 Compact fluorescent fixtures
• 14 SEER heat pump, with ducts inside thermal envelope, fresh air ventilation
• 600 square feet per ton of cooling
• Shading on east and west walls
• Total fill bio-based insulation in walls and roof
• Insulated, low-E, double paned windows
• EnergyStar appliances

Materials:

• Cast earth in first floor walls
• Bio-base total fill insulation
• 100 yr old salvaged French doors, salvaged doors, door hardware
• Reused and salvaged wood and other materials
  

Water:

• Existing vegetation is 90% undisturbed
• Spray irrigation septic system covers zoysia turf grass
• 90% of new plants are from the current City of Austin WaterWise or Grow Green Plant list
• Aerobic waste water utilizes spray irrigation on turfgrass

Health and Safety:

• Formaldehyde free insulation
• Hard-surface flooring throughout
• Thermostat/humidistat runs unit for dehumidification
• Super low VOC paints

Community:

• Existing community
• Pervious driveway
• Built-in recycling center and backyard compost bin

Commissioning and Testing/Results:

• Equipment Sizing Summary: System designed at 609 s.f. per ton which achieves efficient dehumidification
• Blower Door Test: 0.33 ACH (air change per hour)
• Duct Blaster Test: Ductwork located within conditioned space - test not required

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