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“Off Grid” Net Zero Water at Birch Case Study House

2930 Birchwood Ave, Bellingham, WA, USA

Building Type




Lee Phipps | Whatcom County Health Department
Jim Tinner |

Dan Welch | owner
Jim Tinner | approving-official
Lee Phipps | approving-official

This groundbreaking project is the vision of innovative designer Dan Welch of [bundle] design studio in Bellingham, Washington.  Welch designed and built his own home as a case study to validate principles of the Living Building Challenge (LBC), and achieve an “off-grid” Net-Zero Water home.  He and his family now use purified rainwater for all uses and treat all their wastewater on-site, approved through progressive local & state green building codes that allowed him to legally decline City water/sewer hookups.

This home demonstrates multiple innovative solutions to meet the LBC Net-Zero Water imperative; most were easily approved through the advanced codes and standards for water management adopted by the City of Bellingham, Whatcom County Health Department and Washington State Department of Health. Some of the major strategies include rainwater catchment for drinking and all other uses, waterless composting toilets, and treating all greywater and stormwater with on-site infiltration.

By designing his home with innovative closed-loop water systems and high-quality materials, Welch was allowed to go “off-grid” and avoid costly city water-sewer hookups and monthly bills. The City of Bellingham was willing to approve the projects water treatment and disposal system as a stand-alone system if he met the requirement of RCW 19.27.097 which requires “evidence of an adequate water supply.” He applied and got permits from Whatcom County Health Department using adopted guidelines for a) private potable rainwater catchment system (see Rainwater Packet) and b) a Water Conserving On-Site Wastewater Treatment (see DOH #337-016 Recommended Standards and Guidance);  By producing the appropriate permits, City Code officials were satisfied and approved his project. His waterless composting toilets were also approved under the State rules (see separate case study on the Site-built composting toilets at the Birch Case Study House)

Code Requirement Compliance Path
Revised Code of WA RCW 19.27.097requires evidence of adequate water supply By getting County Dept. of Health approval for private rainwater catchment, they satisfied City of Bellingham of adequate water supply, so did not require potable water hookup.  See Bellingham Municipal Code 15.08.020
Whatcom County Code Chapter 24.05and WAC 246-272A regulate the location, design, installation, operation, maintenance, and monitoring of on-site sewage systems (local code has precedence) Code allows infiltration of greywater in on-site septic tank, following state rules for Water Conserving On-Site Wastewater Treatment (DOH #337-016), which allow it to be sized smaller than normal because they use waterless composting toilets (no blackwater).
Square Footage: 2065ft2

Birch House composting toilet diagram

The city of Bellingham actively encourages water conservation, recycling greywater and rainwater harvesting for non-potable uses (see their bulletin AMM 202 and 57-page guidebook).  They also look kindly on potable rainwater.  However both drinking water systems and water conserving on-site wastewater systems are the purview of County Department of Health.  The City does oversee all plumbing installations, under the 2012 Washington State Uniform Plumbing Code (WAC 51-56 and 51-57) w/City of Bellingham amendments.

After hearing from the City that they could avoid having to hook up to municipal water, Welch took his case to the Health Department, using the County’s established guidelines to permit a private rainwater catchment for potable use.

Photos-Philip Dwyer, Bellingham Herald

They had to submit forms for water availability and denial of public water service, and affidavits by the owner and installer taking full responsibility for quality, maintenance and testing the system, signed and filed with the Whatcom County Auditor.

They also submitted all required site plans, system design documents, and a water budget for cistern sizing to ensure adequate year-round supply to the residence.  All materials had to meet NSF standards and water testing following system start up were required prior to occupancy. Finished water quality had to comply with Whatcom County Drinking Water Ordinance and WAC 246-290. Finally a detailed maintenance plan was required to confirm an ongoing effort to maintain a high quality water supply.

For the residential whole-house system rainwater is captured from the roof and gravity fed into two 5,000 gallon tanks. Downspout filters keep large debris from entering the tanks. Water is supplied to the house by a jet pump and passes through a three step filtration process followed by a UV filter for sanitation. All water entering the house, following the filtration process, is potable and tested every year for quality.


They also submitted all required site plans, system design documents, and a water budget for cistern sizing to ensure adequate year-round supply to the residence.  All materials had to meet NSF standards and water testing following system start up were required prior to occupancy. Finished water quality had to comply with Whatcom County Drinking Water Ordinance and WAC 246-290. Finally a detailed maintenance plan was required to confirm an ongoing effort to maintain a high quality water supply.


Project Details:  On-site Greywater Treatment

All water waste from the Birch Case Study House is treated in a small septic tank and infiltrated on site. Sources of waste water include all showers, sinks, laundry and dishes. In the future he hopes to divert greywater from the septic tank to irrigate an orchard and other landscaping, but Whatcom County has yet to approve this type of use.

They also wanted to irrigate an interior solarium planter with greywater to provide more treatment and reuse greywater close to the source. This was in addition to the approved septic system.  Because it was inside the house, the City of Bellingham was the permitting agency for this feature under the Uniform Plumbing Code.  They allowed [bundle] to install the planter as shown in the as-built design (below), but would not approve the system for greywater reuse.  Without documentation from a credentialed public health professional citing research showing no public health risk, the City said they were not in a position to evaluate if greywater under two feet of soil could be safely evaporated & evapo-transpirated with plants.  So the system is installed but awaits further supporting documentation to be approved.

For the outdoor septic tank greywater system as with potable rainwater, Whatcom County Heath Department was the permitting agency.  The system was designed and permitted through the Washington State Department of Health Water Conserving On-Site Wastewater Treatment Systems. This allows for smaller sizing of treatment systems and drainfields when using composting toilets, since all blackwater is diverted from the septic tank and treated separately.  (See related case study on the Site-built composting toilets at the Birch Case Study House)

Project Details:  Stormwater

The Birch Case Study House went to great efforts to control stormwater quantity and quality, and stay under the 5,000 square foot threshold for new impervious surface as required under Bellingham Municipal Code 15.42.  Going above that line could have meant stormwater engineering and potentially detention/treatment, so instead they made the choice to install a permeable driveway and a green roof. City code enforces standards outlined in the 2005 Washington State Department of Ecology Storm Water management Manual for Western Washington which set the 5000 sf limit.

The driveway was installed using Truegrid permeable pavers, a plastic grid paving system. This system sits on top of a free draining aggregate that allows water to pass directly through the driveway and infiltrate into native soils. The pavers also provided a structured fire lane, which was required for firetruck access. The green roof was installed to reduce stormwater quantity by slowing down runoff through the roof soils and plants.  Although the raingardens were not technically required by permit, [bundle] designed and installed two raingardens to help detain any surface water long enough to allow for infiltration. Conveyance to the rain gardens are through wood chip lined ditches which act as “bio-reactors”, which help to treat the water prior to infiltration.

The last component of stormwater management comes back to the beginning of this story:  the rainwater catchment system that supplies potable water.  Rainwater captured from the roof is held in rain cisterns and filtered for potable use and any overflow and all greywater is infiltrated on site through the septic tanks’ drainfield. The detention in the cisterns prevents approximately 800 gallons for every inch of rain from running off the site and into the storm drains during storm events.

Design and installation of both rainwater harvesting and greywater treatment system components within the housewere permitted and inspected by the City of Bellingham and were found in compliance with the Uniform Plumbing Code (w/State and Local Amendments). All plumbing components and installation outside of the house were permitted and inspected by the Whatcom County Department of Health.

Their goal was to develop a project as close to the Living Building Challenge as possible and achieve not only net-zero water but also net-zero energy, and use local sustainable materials throughout the house.  They co-hosted workshops with local environmental group Sustainable Connections to demonstrate the advanced systems and green materials to local builders, at different stages in the construction process.  They partnered with Northwest Energy Efficiency Alliance (NEEA) and Washington State University Cooperative Energy Program to field test an innovative heat pump water heater that uses CO2 as a refrigerant.  The manufacturer Sanden was in the process of obtaining UL listing so this unit can be sold in the US.  See related case study on Birch Home’s Water Heating / Radiant Heat Combotechnology!

Instead of spending thousands on permits and utility construction hookups for City Water and Sewer, Welch was able to invest that money in cisterns, water purifiers, an indoor greywater planter, a small septic tank for greywater, composting toilets, not to mention a green roof and rain gardens to infiltrate stormwater.  They were able to take Net-zero water to (almost) its logical conclusion, without breaking the bank.  Now his family enjoys purified rainwater for all uses including drinking, showers, laundry (there is no toilet flushing), and lives with the satisfaction of knowing their home has gone beyond sustainability to achieve a net-positive impact on the local and global environment.

Among other things, this project shows that when local municipalities and state regulators put innovative codes, policies and guidelines in place, regulatory barriers are largely eliminated. This makes it easier for innovative projects pursuing rigorous green building standards to obtain necessary permits and proceed to construction in a cost-effective and efficient way.  Even going “off-grid” had a clear path to compliance because of the unique interpretation by the City, and County and State enabling rules and processes.  Welch says he didn’t really face a code barrier, it was “more of a clarification. There’s a common misconception that all new construction must hook to the municipal water and sewer systems and pay development charges for these services. This is NOT the case. It just happens we were the first to ask and push the COB to review the code per our off grid request.”  Two features they wanted to install but were not approved for – greywater reuse in an indoor planter, and site-built composting toilets.  These continue to be barriers and were not approved because the statewide rules lack flexibility or sufficient mandate to require local jurisdictions to allow legal use of these systems.

Dan Welch


Jim Tinner
Building Official


Lee Phipps
Environmental Health Specialist