Net Zero Water, Net Zero Energy Full Plane Passive House in Portland

Square Footage: 1950ft²

The owner and design-build team for this home forged an ambitious collaboration to build a beautiful healthy home while going after the most rigorous green building standards in existence:

• A super-insulated, extremely airtight building envelope and advanced heat recovery technology were combined to meet the Passive House standard, verified through modeling performed by Eric Storm.
• Solar Photovoltaics were added to surpass Net-Zero Energy, moving toward net-positive energy; i.e. home producing more energy through renewables than it uses
• The Living Building Challenge, particularly the “Net Zero Water” imperative, which requires the home to capture and use rainwater for everything and handle all wastewater and stormwater on-site.

To achieve Net Zero water, the project utilizes three innovative water systems:

1. Rainwater harvesting for potable and non-potable use, designed in conformance with OSPC Appendix M.   Rainwater is captured from the 1,274 square foot standing seam metal roof surface, and routed through a leaf filter, then to an 11,000 gallon below-grade site-built concrete cistern   The Cistern is sealed with a food grade engineered siloxane coating.  Water from the cistern is drawn through a floating filter that ensures water is taken from the cleanest part of the cistern, filtered again for large particulate matter before being pumped through two in-line filters, which are transparent for easy viewing of filter cleanliness. Water is then routed through a larger carbon filter, and lastly through an ultraviolet purifier. (see attached cistern diagram and product brochures).
2. Graywater reuse for irrigation:  All household wastewater and overflow stormwater from the cistern are distributed via subsurface irrigation to a series of swales and raingardens designed to slow the overland flow of water and promote infiltration, cascading down a 16% slope behind the house.  Landscape zones include a kitchen garden close to the house, another ring with edible fruit trees, shrubs and flowering bee garden, to the outer ring toward the bottom of the hill where a future urban forest has been planted with native shrubs and conifer trees that provide food and nesting materials for butterflies, birds and other wildlife.
3. Composting toilets. Two waterless compositing toilets by Clivus Multrum collect compost solids and liquid leachate in a storage tank in the home’s unconditioned crawlspace. Dry material is mixed with wood shavings and periodically removed to be distributed on-site (per manufacturers recommendation) in an area with non-edible plants growing, and liquid leachate is manually removed and disposed of in the same area.

The recently completed home has quietly reached the ranks of Portland’s most sustainable residences, pursuing Passive House, Net-Zero Energy and the Living Building Challenge standards.

Other strategies include Indoor air quality, maintained with the use of a ductless mini-split system as well as a heat recovery ventilator. An open floor plan supports healthy air circulation. Strategic design provides ample natural daylight throughout the home, streaming through triple pane windows, taking advantage of solar gain in winter and natural shade and ventilation in summer.  The home is constructed with a double stud wall which creates a 12” wide space for dense pack cellulose insulation. The house produces more energy than it uses with a 5kw solar photovoltaic array.

Materials were chosen and utilized to minimize construction waste. Low or zero- VOC paints and zero-toxicity material finishes were used. FSC certified lumber and plywood was sourced by Sustainable Northwest Wood. The exterior siding is low maintenance. The ecological landscape design by The Figure Ground Studio and Fiddlehead, LLC represent regenerative intent to restore natural function to the urban environment. The site is located in a medium-dense neighborhood adjacent to bus routes and bike lanes.

This project was very unique based on the collaboration between the owner, architect, general contractor, landscape architect, and landscape contractor all being at the table from the beginning.  James Arnold, the owner of JRA, commented in a Portland Daily Journal of Commerce article “A little bit of extra planning really helps,” Arnold said. “Once we talk with the subs, the client, our Passive House consultants and everyone, we basically have a hologram of the project in mind and we can hit the ground running.”

James Arnold believes the Full Plane home demonstrates how deep green homes can be built at or below typical custom home costs. Premium costs for additional green building features can be offset by savings derived from an integrated design process and energy incentives.

The home’s water systems have had a few issues, some to be expected, some of them resolved, and others requiring significant retrofits in the hoped-for future.  For example, the gray water system from the kitchen sink was not equipped with a grease trap, and the irrigation system became clogged, requiring them to go back on City sewer until the issue is resolved. Another issue is the engineered siloxane sealant in the rainwater cistern has some small cracks, allowing some erosion of the concrete causing more particulate matter to enter the filtration system, requiring more frequent filter changes.  Because there is no first flush diverter on the rainwater system, impurities get into the cistern requiring periodic use of chlorine sanitation in addition to the UV sanitation.

Normal homeowner maintenance is higher than a traditional house, which was to be expected.  Leaf filters leading to the cistern must be cleared periodically, the cistern itself is cleaned out by scrubbing once per year in the summer, the carbon filters must be changed.  Replacing the UV sanitation bulb is expensive but happens rarely.

• Oregon Statewide Alternative Method 08-01
• 2008 Oregon Specialty Plumbing Code Appendix M
• OAR 340-071 Onsite Wastewater Treatment Systems
• OAR 918-770-0080 Composting Toilets