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 HumanitySpecs:Location: Prescott, ArizonaCompleted: 2006Bedrooms: 3Bathrooms: 2Cost: $55/square footSize: 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 upHERS 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
Energy efficiency measures used in this project
Green materials and/or resource efficiency used in this project
Indoor air quality measures used in this project
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 UtilizationSolar 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 SystemLessons 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.
From top to bottom, the platinum-rated house embodies a best-practices approach to the building envelope. The framing makes extra room for insulation with 24-in. on-center spacing, two-stud corners, and offset rim joists. Damp-spray and dense-pack cellulose insulation does an excellent job of filling wall cavities. To make sure they didn’t miss anything, the project team did a blowerdoor test before the drywall went up so that any leaks could be filled.The 2.6-acre rural maine lot wasn’t eligible for many of the 'lot location' credits, but the team did pick up a few points for not disturbing wetlands, building in a floodplain, or on agricultural land.
To mitigate the effects of development, the property has a permeable gravel driveway that absorbs water runoff. even with a septic system installed, more than 40% of the site was left undisturbed. excavated and trafficked portions were replanted with a mixture of native wildflowers and drought-resistant fescue grass.
Construction:Foundation type: ICF Basement, R-23Wall construction: 2x6, 24 in. o.c. with dense pack cellulose, R-R-21Windows: Thermotech triple glazed, U-.15 (R-6.7)Attic: R-49 loose fill cellulose in ceilingGarage: Attached.
Energy specs:Conditioning equipment (explain): Radiant floor and wood stove. No cooling systemWater heating equipment: Solar water heaterHERS Index: 42Water efficiency measures used in this projectLavatory faucets: max 1.5 GPMShower heads: max 1.5 GPMToilets: max 1.1 GPM, dual flush (Mansfield EcoQuantum)
Energy efficiency measures used in this projectFluorescent fixtures represent more than half of the installed lighting, solar hot water system is plumbed so that excess capacity assists the radiant heating system, siting of building and layout of windows facilitate passive solar heating, effective daylighting and natural ventilationGreen materials and/or resource efficiency used in this projectFSC certified lumber and advanced framing techniques. Wheatcore doors, Dakota Burl cabinet panels, recycled content floor tile, fly ash in concrete, recycled content metal roofing, no carpet, low-VOC paints, and cellulose insulation. Locally sourced materials include birch flooring, stair parts, framing lumber, cedar siding, and granite countertops.Indoor air quality measures used in this projectHeat recovery ventilator with air distributed through ducts. Low VOC paint was used throughout. The garage has a ventilation fan actuated by the garage door openers. There is no air conditioning.
Certification: LEED-H Platinum, overall score: 95/130Innovation and design 9/9Energy and atmosphere 27/38Location and linkages 3/10Materials and resources 14/14Sustainable sites 15/21Indoor environmental quality 15/20Water efficiency 10/15Awareness and education 2/3Alternate Energy UtilizationPhotovoltaic power (:2 KWSolar water heating :3 collectorsGreen Building Product Sources:Lessons Learned:The house has performed very well. The build team intially intended the house to be smaller, but a real estate consultant recommended building a master bedroom suite over the garage. Also, the house is in the suburbs, which does not help the problem of sprawl.
