This house proves that green doesn't mean expensive.
This rather typical 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 inn the face of green building conventional wisdom. How did they do it? Tradeoffs. Fewer studs means more room for insulation. Roof overhangs and quality windows means a smaller AC system. Unvented roof means the AC and ducts can go in the attic.
The cost savings began with the site: a substandard lot (flood plain issues) was engineered to bring it up to code standards. While there was a high level of engineering, it was kept localized as much as possible -- many existing trees and shrubs were spared. No toxic pesticiedes were sprayed before construction, 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 which heat the water for free.
Advanced framing, exterior foam insulation, and an unvented roof yielded an extremely tight envelope -- .63 ACH, at no "extra" cost. Smart plumbinf layout cuts the amount of time waiting fore hot water to reach a tap, which saves water. Much of the techniques used in 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, Better windows are worth it.
Team:
Builder: Yavapai College Residential Building Technology Program, Tony Grahame Director.
Architect/Designer: Prescott area Habitat for Humanity
Specs:
Location: Prescott, Arizona
Completed: 2006
Bedrooms: 3
Bathrooms: 2
Cost: $55/square foot
Size: 1,189 sq.ft.
Construction:
Foundation type: Slab on grade with XPS foam at edge (R-5)
Wall construction: 2x4 @ 24 in. o.c., 1 in. XPS foam and dense pack cellulose (R-19 total)
Roof: Raised heal 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
Energy specs:
Conditioning equipment: 14 SEER Energy Star AC system; 40,000 BTU direct vent gas furnace (92.0 AFUE)
Water heating equipment: Solar domestic hot water system, 40.9 sq.ft. flat plate collector, 80 gal. storage tank with electric back up
HERS Rating: 57 (5 stars)
Yearly Energy Use (electric, gas, heating oil combined)
Modeled or predicted: (kBTU/sf):
Actual : (kBTU/sf):
Water efficiency measures used in this project
- Low flow toilets, faucets, and shower heads
- Water conserving Energy Star dishwasher
- All hot water taps within 30 ft. of hot water storage tank
Energy efficiency measures used in this project
- 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 including dishwasher and refrigerator
- HVAC requirements calculated and sized appropriately
- Programmable thermostats
- Sealed ductwork, Duct Blaster leakage measured 14 cfm @ 25 Pascals
Green materials and/or resource efficiency used in this project
- Advanced framing
- house designed in 2ft. increments to conserve materials
- Cellulose insulation made with recycled paper
- Composite decking contains recycled plastic
- cardboard and metal construction waste was recycled
Indoor air quality measures used in this project
- Balanced whole-house ventilation with MERV-10 and HEPA filtration.
- Moisture mitigation techniques including damp-proof subslab, soil surface gaded away from house, foundation drains around perimeter, plastic sheet under slab, wall system design allows drying to inside and outside, right sized HVAC controls humidity
- Garage is pressure isolated from living space
- Radon venting
- Only hard surfaced flooring, no carpet
- Multiple return grills provide pressure balancing between rooms
- All ductwork is within conditioned space
- Spot ventilation in bathrooms
Certification:
EnergyStar: qualified based on HERS score (57)
NAHB green score with breakdown of points earned/available:
Other certification with breakdown of points earned/available:
Alternate Energy Utilization
Solar water heating (type and size of system): 40.9sq.ft. SunEarth flat plate collector, Solaraide 80 gallon hot water storage tank/electric backup heater; cost $_________
Green Building Product Sources:
Eljen In-Drain Geotextile Sand Filter System
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.
