The Northwestern section of the United States has earned a reputation for encouraging “green” building. For example, the mayor of Seattle, WA joined the mayors of Miami, Chicago and Albuquerque to present a resolution to the U.S. Conference of Mayors in May 2006 to adopt the 2030 Challenge. While the 2030 Challenge stipulates that buildings be carbon neutral, the goal to create environmentally friendly buildings has often been in the minds of officials in Washington. In keeping with this ethic, Issaquah, WA city officials gave a nearly half acre parcel of the Issaquah Highlands to a project developer with the stipulation that the project be constructed to meet certain impressive sustainability requirements. The project for this site was conceived as a ten-unit, zero energy, zero carbon community. Thus zHome was created. David Vandervort Architects (DVA) was selected as the project Architect for the job.
The creation of market-ready homes that provide a community as well as meet strict environmental standards (such as netZero energy) requires constant monitoring of the design aesthetic as well as a way to demonstrate the way the building will operate. It involves more than just throwing solar panels and energy efficient windows into the mix. DVA had to create a welcoming space that operated well within climatic constraints and city standards.
The site plan began with the idea of ganging the units around a central courtyard. This “solar courtyard” serves as a community space for the residents to access common entrances and shared space. Using ArchiCAD, the team started sketching a 3D model that would be appropriate to the suburban, highlands area. The concept of creating a loft style of home grew from there. ArchiCAD BIM was also used to show the client how the spaces were going to feel inside and how they’d relate to the outside. The architect was able to demonstrate this relationship clearly with a cross section of the building model.
For the most part, the dwellings have main living levels on the second floor, in order to enhance privacy of the individual units. The dwellings range in size from one, two and three bedrooms. The majority of the available units have been sold – they range from $370-599K – which is close to market price for similar sized units. The layouts of the units are designed to be open and large – so that residents can make the most of smaller spaces. One bedroom units measure roughly 800 square feet. The largest units are 1500 square feet. Each unit has open beam ceilings and use FSC lumber throughout.
“Being able to model what you’re creating as you’re designing it with BIM is powerful,” explained lead DVA architect on the zHome project, Mark Wierenga, Associate, LEED-AP. “We were able to quickly show exactly what we were talking about doing. This aspect of our workflow really helped us work with the city officials and keep everyone on the same page.”
The City of Issaquah set aggressive environmental benchmarks on the project; covering energy use, carbon emissions, water consumption and use, material efficiency, etc. For energy, the stated goal was that the buildings consume no more energy in the course of the year than can be generated on site. During the design phase, DVA worked with the mechanical design consultant to determine electrical loads for every dwelling unit in every building. The decision was made to design an energy efficient envelope, using high levels of insulation and extremely airtight construction methods. Paired with this efficient envelope is an efficient heating technology: ground source heat pumps. These heat pumps extract heat from a liquid that is circulated through tubes in the ground. Extracted heat is used for both domestic hot water and space heat for the dwellings.
Energy produced on site is done so with photovoltaic panels. Each dwelling is provided with a grid-tied PV array that is between 4 and 6 Kilowatts. Given that the northwest has long summer days, a surplus of power is generated in the summer months, which makes up for the power used during the winter months. Solar exposure was a huge factor in determining energy use. DVA used solar studies within ArchiCAD to calculate shading and the best way to make use of the single pitch roofs. The site planning took care of that for them; they developed options directly in the model and ran a series of sun studies. They made sure that none of the PV panels were shaded and even factored in a worst-case scenario proposing what might happen if a nearby building were to increase its height to the maximum allowed by zoning requirements.
Due to the large number of stakeholders involved in this project, the architect had to work closely with a variety of consultants. As such, easy data sharing was crucial to the success of the project. “As we worked with consultants on this project, we found data sharing very simple, even in situations where they may have been using other BIM software. We never had any problems whatsoever and have noticed that the DWG translators in ArchiCAD get better every year.”
Knowing that the methods used to achieve zHome’s high efficiency standards would serve as a guide for future projects, city officials arranged to maintain one unit of zHome dwellings as a Stewardship Center. This unit serves as a model for tours, and to demonstrate the energy efficient features of the homes and to display the technology that went into creating them. The idea was to create an impressive design that functioned at netZero – so that there could be a standard by which to judge other such buildings.