April 15, 1994
Mixed-Humid

Abstract: 

They will sell for under $80,000 each, making them affordable to families earning less than 80 percent of the median income in the Dallas metropolitan area (under $35,000). Monthly payments will range between $500 to $700 per month. Utility costs (heating, cooling, and hot water) are expected to be $30 per month. Typical utility costs for houses of similar size in Dallas have ranged Between $80 and $100 per month. The building system design resulted in a 60-to-70 percent reduction in energy consumption. A minimum of $50 per month for utility cost will be saved.

Introduction

Twelve affordable , healthy, environmentally responsible single family houses were designed and built on an urban infill in Dallas, Texas. They will sell for under $80,000 each, making them affordable to families earning less than 80 percent of the median income in the Dallas metropolitan area (under $35,000). Monthly payments will range between $500 to $700 per month. Utility costs (heating, cooling, and hot water) are expected to be $30 per month. Typical utility costs for houses of similar size in Dallas have ranged Between $80 and $100 per month. The building system design resulted in a 60 to 70 percent reduction in energy consumption. A minimum of $50 per month for utility cost will be saved.

The two story 1273 sq. ft. houses are arranged around two central green spaces with service corridors in the back for parking and trash pick-up. Each house lot contains approximately 1900 sq. ft. and includes parking for two cars as well as over 800 sq. ft. of outside space. This project achieves a density of 15 units per acre while being compatible with existing neighborhood housing. Sunlight brightens courtyards and other outside spaces such as uncovered balconies and covered porches for the majority of the day during a majority of the year. Windows and doors are placed to allow maximum natural light and ventilation. Unwanted summer solar gain is held to a minimum by avoiding window placement on the southwest elevations, selective use of overhangs, and selective placement of deciduous trees.

The building enclosure was designed with an exterior air retarder system to achieve maximum air tightness (1.5 square inches of leakage area per 100 sq. ft. of building enclosure surface area). Low envelope leakage and high insulation levels allowed for a low flow air distribution system. The floor trusses were used to create a floor plenum distribution system. The low heat gain and loss figures meant a small geothermal heat pump unit could be used for heating, cooling and hot water production. A simple and inexpensive controlled ventilation system was designed that allowed control of air pressure differences throughout the year .

The Priorities

Sustainability is generally defined as a commitment to meet our present needs without compromising the ability of future generations to meet their needs. As team members of a building development project, we have a responsibility to help ensure a sustainable development. The effects of building development on the environment are:

  1. The creation the interior environment in which people must live and work.
  2. The expenditure of huge amounts of natural resources (many of which are not renewable)
  3. The creation of a machine that continues to need to be fed (energy is needed to run a building).

The effects of building development on the environment are at the most basic level about durability. Building a house or community is really about the durability of people (health, safety, and well being of people), the durability of buildings (the useful service life of a building is typically limited by its durability), and the durability of the planet (the well being of the local and global environment) . Durability is really another way of expressing the concept of sustainability to the building community.

When we build a building, a system is created that is an interaction of people, buildings and the environment. Making decisions about buildings requires prioritizing to reconcile the various needs of people, buildings and the environment. For example consider the needs of the people before considering the needs of the building. Consider the environment created by a building before considering the planetary environment. Resolve local concerns before resolving global concerns.

Goals

  1. Create buildings that ensure a healthy environment for its occupants thereby promoting health for future generations.
  2. Deliver buildings that are durable (life expectancy of 100 years with only minimal replacement of parts needed) thereby reducing future waste and depletion of natural resources.
  3. Deliver that have a low total energy consumption during their lifetime. They must have a low operating energy since operating energy account for 60% to 70% of total energy consumption (Total energy = operating energy + embodied energy + decommissioning energy).

Design Priorities

1. Health and Safety: Exclude pollutants from conditioned spaces by:

  • selecting, installing, operating and maintaining heating, cooling and ventilation equipment appropriately
  • controlling the air pressures between the conditioned and unconditioned spaces as well as between rooms and interstitial spaces
  • selecting appropriate building materials and installing and maintaining them correctly
  • maintaining buildings in an appropriate manner and selecting appropriate housekeeping practices

Operate buildings so that pollutants are removed from conditioned spaces. Use controlled mechanical ventilation to accomplish this. Construct building enclosures and mechanical system duct work in a leak free, tight manner to control air pressure differences, thereby excluding environmental pollutants.

2. Comfort: Create comfortable buildings with respect to temperature, humidity, odors, sound/vibration and light by:

  • using thermal insulation
  • selecting efficient space conditioning systems
  • designing and building leak free building enclosures and mechanical system duct work
  • providing controlled mechanical ventilation and exclusion of pollutants
  • selecting efficient glazing systems and using natural lighting
  • operating buildings correctly and maintaining and cleaning them appropriately

3. Affordability: Create efficient buildings with respect to their use of energy, water and materials by:

  • designing buildings that are efficient in their layout and use of interior space
  • using thermal insulation to reduce operating costs
  • selecting efficient space conditioning systems, equipment and lighting
  • selecting efficient glazing systems
  • providing controlled ventilation
  • controlling the building envelope air leakage
  • selecting appropriate materials
  • constructing, operating and maintaining buildings in an appropriate manner.

4. Useful Service Life: Build durable buildings. Accomplish this by:

  • preventing buildings from getting wet during construction
  • allowing wall assemblies to dry should they get wet (sometimes referred to as a "forgiving" assembly) during construction and/or operation.

5. Environment: Build and operate buildings with a minimum of waste. Select materials and sites with respect to their local and global impact. Accomplish this by:

  • reducing additional underground utility development by choosing sites with underground utilities in place
  • recycling inner city infill sites when possible
  • reducing construction water
  • reducing operating water
  • recycling construction waste
  • recycling operating waste
  • controlling soil erosion during site preparation and construction
  • infiltrating storm water back into site
  • controlling air pollution during construction and operation
  • avoiding ozone depleting materials and systems
  • using materials from managed forests and managed mineral extraction and processing
  • reducing operating energy
  • reducing embodied energy . . .

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