GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted
Green Homes

A Modest New House Proves Green Doesn’t Mean Expensive

The home looks conventional, but it is the result of an integrated design full of sustainable concepts and materials.
Image Credit: Tony Grahame
View Gallery 6 images
XPS rigid foam creates a thermal break between the concrete slab and the foundation wall.
Image Credit: Tony Grahame
Sprayed polyurethane foam and rigid XPS foam with taped seams are very effective as insulation and air barriers.
Image Credit: Tony Grahame
Engineered trusses and advanced-framing methods make room for plenty of insulation and use less materials than a typical house. All headers in the home are insulated with XPS foam.
Image Credit: Tony Grahame
The home gets most of its domestic hot water from a flat plate solar collector.
Image Credit: Tony Grahame
Image Credit: Toshi Woudenberg TOP 25% OF AMERICAN HOUSES: 40.8 MMBtu/year. There's nothing particularly complicated about this home - it's just built very well. The large crew of student laborers from the Yavapai College Residential Building Technology program may have made it easier to find every possible air leak in this thoroughly sealed, mechanically ventilated home. But that's not to say that a well informed, concientious contractor wouldn't be just as succesful at building an affordable, energy efficient home.

#Typical Looking, Uncommonly Efficient and Healthy

This rather typical-looking single-story ranch house is very uncommon in a lot of ways. It’s super energy-efficient, it has superior indoor air quality compared to most new houses, and it cost $55/square foot to build.

That it was so cheap to build flies in the face of conventional thinking about green building. How was this done? Tradeoffs. Fewer studs means more room for insulation. Roof overhangs and quality windows mean a smaller AC system. An unvented roof means the AC and ducts can go in the attic.

Make the site work without overdoing it
The cost savings began with the site: a substandard lot (thanks to flood-plain issues) was engineered to bring it up to code. While there was a high level of engineering involved, the lot was kept localized as much as possible — many existing trees and shrubs were spared. No toxic pesticides were sprayed before construction, and the house is oriented along an east-west axis to maximize southern exposure for day lighting, passive warming in winter, and solar collectors on the roof that heat the water for free.

Standard green details done well
Advanced framing, exterior foam insulation, and an unvented roof yielded an extremely tight envelope — .63 ACH, at no “extra” cost. A smart plumbing layout cuts the amount of time it takes for hot water to reach a tap, which saves water. Many of the techniques used in the design and construction of this house are old news: insulating a slab keeps it warm and dry; foam sheathing on the outside keeps the framing warm and dry, so mold isn’t likely to gain a foothold; and better windows are worth it.


Lessons Learned

Because of the small lot size, a standard septic leach field was not feasible for this project. Tony Grahame, director of Yavapai College's Residential Building Technology program, solved this problem with the Geotextile Sand Filter system made by Eljen.

A plastic grid covered in a special drainage fabric allows for more surface area, more volume, and more air infiltration than the typical bed of gravel. The result is that you get a leach field that will likely perform better while taking up 50% less space. Using this system was the only way to build a home on this particular site, but it would be valuable to anyone trying to keep site disturbances to a minimum.

General Specs and Team

Location: Prescott, AZ
Bedrooms: 3
Bathrooms: 2
Living Space: 1189
Cost: 55
Additional Notes:

Student labor was free

Builder: Yavapai College Residential Building Technology program; Tony Grahame, Director.
Architect/designer: Prescott-area Habitat for Humanity


Foundation: slab on grade with XPS foam at edge (R-5)
Walls: 2x4 @ 24 in. o.c.; 1-in. XPS foam and dense-pack cellulose (R-19 total)
Roof: raised heel trusses; 8 in. foam sprayed to underside of roof deck (R-32, unvented).
Windows: double-pane, low-e, argon-filled (SHGC, .33 to .35; U factor, 0.32 to 0.35, R-3)
Garage: attached; insulated and sealed from living space


  • Roof overhangs optimally sized for window heights to allow summer window shading and winter sun entry for passive solar heating.
  • Energy Star interior and exterior lighting package with CFL bulbs
  • Extremely tight building envelope (103 cfm @ 50 pascals equivalent to 0.63 ACH)
  • Energy Star appliances
  • HVAC requirements calculated and sized appropriately
  • Programmable thermostats
  • Sealed ductwork; duct blaster leakage measured 14 cfm @ 25 Pascals

Energy Specs

Heating/cooling: 14-SEER Energy Star AC system; 40,000 BTU direct-vent gas furnace (92.0 AFUE)
Water heating: solar domestic hot-water system, 40.9 sq. ft. flat-plate collector, 80-gal. storage tank with electric backup
HERS rating: 57 (5 stars)
Annual energy use: 40.8 MMBtu

Water Efficiency

  • Low-flow toilets, faucets, and showerheads
  • Water-conserving dishwasher
  • All hot water taps within 30 ft. of hot-water storage tank

Indoor Air Quality

  • Balanced whole-house ventilation with MERV-10 and HEPA filtration
  • Moisture-mitigation techniques including damp-proof subslab, soil surface graded away from house, foundation drains around perimeter, plastic sheet under slab, wall system designed for drying to inside and outside, appropriately size HVAC controls humidity
  • Garage pressure-isolated from living space
  • Radon venting
  • No carpets
  • Multiple-return grills provide pressure-balancing between rooms
  • All ductwork within conditioned space
  • Spot ventilation in bathrooms

Green Materials and Resource Efficiency

  • Advanced framing techniques
  • House designed in 2-ft. increments to conserve materials
  • Cellulose insulation made with recycled paper
  • Composite decking contains recycled plastic
  • Cardboard and metal construction waste recycled

Alternate Energy Utilization

Solar water heating: 40.9sq.ft. SunEarth flat-plate collector; Solaraide 80-gallon hot-water storage tank/electric backup heater


NAHB Energy Value Housing Award: gold
EnergyStar: qualified based on HERS score (57)


  1. Expert Member
    CARL SEVILLE | | #1

    Checking on the true cost
    This is certainly an admirable project and I very much appreciate the simplicity of the efficiency - fewer high priced/high tech products and lots of good, simple decisions. I would like to understand what the relative cost of this house if all the labor was included at market rates instead of donated student time. We need to see more projects like this completed with the structure of the marketplace.

  2. homedesign | | #2

    This project illustrates a
    This project illustrates a lot of good concepts that can be translated to any climate zone. Comfortable,Efficient and Affordable.

  3. mapnerd | | #3

    Some good ideas...
    This is a useful case study. Even though the labor costs and overall house size aren't the most useful comparisons, there are a lot of interesting ideas here. Some of the concepts I'm now thinking about are solar water heating (are flat panels a better long-term value vs evacuated tubes??), 2x4 (24" oc)/2x6 (24" oc) with good insulation vs ICF/SIP's, Geotextile sand filters instead of standard septic laterals, and unvented roof with ductwork in conditioned space (how does that work?). Thanks for posting this project! I'm getting some great ideas from the case studies.

  4. Chris Builder | | #4

    Home Remodeling
    Thanks for this. Always looking for new approaches to green construction. The Geotextile Sand Filter system sounds like an impressive innovation. In my area lots are getting smaller and smaller as property prices rise, so any and all space-saving efficiencies are well appreciated. I'm going to check out the Eljen website right now! Thanks.

  5. Derek Vander Hoop | | #5

    40,000 BTU furnace?
    It seems to me that a home with 2x4 walls filled with dense pack cellulose and 1" of XPS foam on the exterior, located in Arizona, that is only 1200 square feet would not need a 40000 BTU furnace, particularly if attention was paid to the air barrier. Oversized, perhaps? Having said that, it is hard to find conventional furnaces manufactured with a lower BTU rating.

Log in or create an account to post a comment.


  • Green Homes

    Energy-Efficient Straw-bale Home in the Colorado Rockies

    By Doug Graybeal Our house is located outside of Carbondale, Colo., at an altitude of 7,000 feet. The architecture is both responsive to the climate — a dry mountain environment…

  • Green Homes

    Sustainable Materials and Solar Power in the Southwest

    Bau-Biologie—a construction philosophy focused on using natural materials to build healthy homes—originated in Germany, but in the USA, one epicenter is just outside of Santa Fe. Here, architect Paula Baker-Laporte…

  • Green Homes

    1970s Home Goes Net Zero

    Intensive renovation has made this modest ranch house in the suburbs of Boulder, Colorado, an example of what all green builders strive for — a net zero energy home. Changes…

  • Green Homes

    Green Neighborhood in North Carolina

    #Twenty-two homes in a cluster made for walking Eno Commons takes the idea of green homebuilding to another level — the community level. The Durham, North Carolina, project includes 22…


Recent Questions and Replies

  • |
  • |
  • |
  • |