Water Conservation, Energy Efficiency, Indoor Air Quality, Materials Efficiency, Design Innovation, Solar Power, Storm Water Infiltration, Advanced Building Envelope
Set on a hilltop above the town of Carnation, the view is stunning. It took five long years for the homeowners to build their dream house themselves. Their new Passivhaus is powered solely by PV and solar hot water, uses 100% harvested rainwater, and is certified Built Green 5 Star.
- Client: Marian and Gary Aamodt (“AAH-mutt”), middle aged couple, empty nesters
- Scope: new single family house, 1 story, with attached 4 car garage, pre-certified Passivhaus
- Address: 33015 NE 50th Place, Carnation WA 98014
- Location: hill top in Cascade foothills about a half mile outside small rural town of Carnation WA
- Site: 20 acres, steeply sloped, previously cleared, 270° view to southwest of mountains and farm valley
- Completed house: 1638 ft2 conditioned (1340 ft2 TFA), 1106 ft2 garage, 496 ft2 decks
- Rooms: 3 bedrooms, 2 baths, living/dining/kitchen, dressing/walk-in closet, laundry, mud room
- Costs (labor and materials): [overall cost confidential]; $32k PV system, $8k solar hot water system, $32k rainwater harvesting system, $47k windows and doors, $10k exterior window shade system, $6k rigid foam at floor and roof, $12k septic system, $39k electrical service, $10k tree planting
- Schedule: 6 months to design, 5 years for owners to construct
- Architect: VELOCIPEDE architects inc, Seattle WA
- Rainwater system: Chris Webb and Associates, Inc., Bellingham WA
- Passive House v2007 PHPP (national energy efficiency certification program)
- Built Green 5 Star v2007 (King / Snohomish County green building certification program)
- All windows are fiberglass frames with EPS foam in the cavities, Cascadia series 325 and 400.
- All windows are triple glazed, with argon fill and stainless steel spacers, U=0.27 (about R-3.7).
- The solid garage entry door is fiberglass faced with polyurethane foam core, U=0.14 (about R-7) and the front entry door is U=0.21 (about R-5).
- Exterior walls are double stud, advanced framed with minimized thermal bridging.
- Ceiling insulated to R-75, walls insulated to R-40, floor insulated to R-50.
- Exterior walls, floor, and the ceiling are insulated with blown in cellulose to completely fill all cavities.
- The entire floor and entire ceiling are air sealed and insulated with 3” of foil faced polyiso foam.
- The exterior walls are wrapped with a double air barrier (plywood, Tyvek) to eliminate infiltration.
- The envelope air tightness was tested with a blower door apparatus at 0.47 preliminary ACH50.
Solar heat management
- Solar cool steel roofing with a Solar Reflective Index of 34 reflects unwanted summer sun.
- Roof overhangs of 2 feet block unwanted summer sun.
- Exterior shades to block unwanted south and west sun.
- Solar selective window glass admits 56% of the sun’s heat when the shades are up (SHGC=0.56).
- Modeling using PHPP software was utilized from the first week of design to shape the building.
- eGauge system monitors total production, total consumption, and 3 individual electric circuits.
- User interface is web based and customizable with real-time monitoring.
- Power draw for monitoring system is 7.5 watts max, 2 watts typical.
- Fresh air ventilation is by a Zehnder 350 HRV with a 95% sensible effectiveness.
- Ventilation distribution is by Zehnder Comfo-tube polyethylene tubes that are entirely inside the conditioned space.
- Space heating is by the ventilation system, supplemented by a 2000W electric resistance duct heater.
- Water heating is by solar collectors with an electric back-up element in the potable storage tank.
- Solar hot water collectors are two Apricus APCP-20 (40 evacuated tubes total), which generate 2,645 kWh/yr = 125 therms/yr = 12,540,000 BTU/yr, mounted fixed at 34 degree tilt and 44 degrees east of true south azimuth.
- Solar hot water tank is an 80 gallon Rheem 81-V80-HE-1 with electric element water heater.
- Electricity generation from the sun is by an 8.5 kW STC photovoltaic system that is grid-tied.
- PV panels are 26 each SunPower SPR-E20-327-WHT, mounted fixed at 34 degree tilt and 44 degrees east of true south azimuth.
- PV inverter is SMA Sunny Boy SPS7700TL for grid tie with 1500 W daytime power available in the event of a power outage.
- Energy Star rated clothes washer (109 kWh/year), refrigerator (633 kWh/year), and dishwasher (270 kWh).
- The clothes dryer is a condensing type that does not remove heated air from the house interior.
- Used a mixture of compact fluorescent (garage) and LED lighting (entire house).
- Total lighting wattage for the house is just 292 watts, a remarkably low 0.18 watts per square foot.
- Only incandescent lighting anywhere in the project is three lamps in microwave/range hood.
- Large windows and solar selective window glass allow 70% of visible light to brighten the interior.
- All walls are advanced framed to reduce installed lumber by about 1100 board feet without sacrificing strength.
- The flooring, window sash, steel siding, and steel roofing were prefinished at the factory, eliminating field painting and future repainting.
- Purchased used scaffolding and re-sold when finished.
- Guest bath vanity is a re-purposed dresser.
- Temporary power pole/breaker box/breakers were re-sold on Craigslist.
Recycling at the job site
- Of the total 8250 pounds of waste (cardboard, metal, gypsum wallboard, concrete, roofing, etc.) generated during construction, 89% was recycled, a total of 7350 pounds.
- Only 900 pounds of waste was sent to the landfill.
Recycled content materials
- The structural concrete in the project is 4% fly ash slag (35% of cementitious content), a waste product from coal burning power plants.
- The rebar steel in the project is 97% recycled content from post consumer steel scrap.
- The blown insulation in the project is Green Fiber 765 LD 85% recycled content cellulose from deinked newspapers.
- Rebar chairs are recycled plastic.
- Guest bath tub is 80% recycled steel.
- Laundry tub is 80% recycled steel.
- Interior sound-dampening insulation is 80% recycled denim.
- Waterway drain mat behind exterior siding is 40% recycled polypropylene.
Indoor air quality
- There is no carpet in the house.
- There is no particleboard in the house.
- All cabinets, sheathing, and engineered lumber used in the house is No Added Urea Formaldehyde.
- During interior sanding and painting operations, the house interior was mechanically ventilated to the exterior.
- The mechanical ventilation system provides only fresh air to the interior, filtered to MERV 13.
- All ducts were carefully protected throughout construction.
- The Behr Premium Plus interior wall paint used contains no formaldehyde (a carcinogen), and has a VOC of zero g/l.
- Only low VOC (50 g/l or less) adhesives, sealants, and caulks were used inside the house.
- All framing was done under a tarp to keep the primary structure dry until it was enclosed.
- No smoking was permitted anywhere on the construction site.
- Only low toxic and low VOC cleaning products were used by the homeowners prior to occupancy.
- All the plywood wall, floor, and roof sheathing is certified to be sustainably harvested by the FSC.
- All framing lumber (except the roof trusses) including the floor joists, rim joists, and laminated beams and posts are certified to be sustainably harvested by the FSC.
- All interior wood trim is pine certified to be sustainably harvested by the FSC.
- The wood interior trim is finished with Behr paint, a water based acrylic with 0 VOC.
- Each yard of concrete in the project has only 336 pounds of Portland cement, just two thirds the cement of a typical 5-1/2 sack (517 pound) mix, saving 40 pounds of CO2e in manufacturing energy.
- PVC avoided in the project:
- ABS plumbing waste pipe (no PVC).
- Fiberglass window sash (no PVC).
- Steel electrical boxes (no PVC).
- Nylon electrical outlets, switches, and cover plates (no PVC).
- Minimal PVC used in the project:
- PVC insulation on electrical wire, only kind available in USA.
- 36% fiberglass, 64% vinyl fabric for operable sunshades, Greenguard Gold Certified.
- Only vegetable based, not petroleum based, oil was used on concrete forms.
- No preservative treated wood was used inside or outside the building.
- Only rigid insulation foamed with pentane was used on the project, a zero Ozone Depletion Potential (ODP = 0) and low Global Warming Potential (GWP < 5) gas.
- Potentially 100% of the energy used annually inside the house will be provided by the solar energy falling on the outside of the house (net zero energy). To be confirmed upon one year of occupancy.
- 100% of the rain that falls on the building roof is directed to a dispersion trench and evaporates to the sky or infiltrates into the earth without leaving the site.
- All waste water (blackwater and graywater) is discharged to the conventional on-site septic system.
- This project obtained the first permit for potable use of only harvested rainwater in King County.
- All rain that falls on the house roof is collected for reuse in one NSF certified galvanized steel tank on grade with a PVC liner, total capacity 8,800 gallons.
- Rainwater filtered to 0.5 micron and sterilized with UV is used for 100% of potable water used inside the house for bathing, cleaning, cooking, drinking and plants (both inside and out).
Efficient plumbing fixtures
- Both toilets in the house are dual flush, using either 1.0 or 1.6 gallons per flush.
- The laundry machine in the house uses 10 gallons per cycle.
- Existing top soil was stripped, reserved on site, and reinstalled, about 30 cubic yards.
- All excavated dirt at the site was redistributed on the site, with none exported off site.
- All temporary dirt piles were covered with tarps to eliminate wind and rain erosion.
- Silt fencing was installed at the site perimeter for the duration of construction.
- The previously clear-cut steep slopes were replanted with 2730 trees (920 Douglas fir, 800 Ponderosa pine, 500 Western White pine, 150 Shore pine, 100 Hemlock, 100 Sitka spruce, 100 Red Osier dogwood, 30 Oregon oak, and 30 Oregon ash).
Drought tolerant plants
- All new decorative plants are species that require no irrigation after establishment.
- A 2-acre wildlife foraging area around the house was planted with 920 plants as a wildlife food source (100 Indian Plum, 100 Twinberry, 100 Snowberry, 100 Red Elderberry, 150 Blue Elderberry, 150 Serviceberry, 170 Mock Orange, 50 Evergreen Huckleberry).
Low impact transportation
- One of the homeowners telecommutes 5 days a week.