The Largest Passivhaus Building in the U.S.
The Orchards at Orenco will be a 57-unit affordable housing project near Portland, Oregon
In Portland’s western suburbs, a structure is on the rise that could change the face of affordable housing in America. Situated adjacent to the Orenco Station light rail transit stop in Hillsboro, Oregon, the Orchards at Orenco will provide 57 units of housing. The project sponsor, REACH Community Development, is aiming to achieve Passivhaus certification. When complete in the spring of 2015, Orchards at Orenco is slated to be the largest Passivhaus-certified building in North America.
REACH is a non-profit developer dedicated to lowering overall living costs for the residents in their housing. In REACH’s view, delivering truly affordable housing means delivering housing that places a minimal burden on the finances of low-income families by keeping utility costs as low as possible. Additionally, housing should ideally be located in close proximity to regional transit lines to provide residents with accessible, low-cost travel options.
An L-shaped building
The building has an L shape, with two wings of residential units and a “knuckle” of common spaces at the corner (see Image #6, below). Although in terms of energy-efficient design, the building form is not optimal — either from an orientation or massing standpoint — the L shape was required to meet urban design guidelines in the Orenco Station district of Hillsboro.
During schematic design, the project team chose to remove the trash room, elevator, laundry rooms, and fitness room from the conditioned Passivhaus envelope. These spaces require high ventilation rates. If the spaces had been located inside of the Passivhaus zone, the large volumes of conditioned air that will be exhausted from the building would have made it difficult to attain the Passivhaus goal.
There were also concerns about the degree of airtightness that could be achieved at these spaces given the number and size of vents that would be required at the laundry rooms and elevator shaft. This early decision has had significant ramifications on later design decisions and is currently being studied for revision as construction is progressing.
The three-story wood-framed building sits on a slab-on-grade foundation (see Image #1, above). Typical exterior walls have 2x10 framing with blown-in fiberglass cavity insulation and 1 1/2-inch-thick rigid mineral wool exterior insulation (see Image #7, below). Mineral wool was chosen due to its permeability and capacity to facilitate drying to the exterior.
At the exterior walls, the plywood sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. (with taped seams) serves as the primary air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.. Plastic housewrap installed over the sheathing serves as the water-resistive barrierSometimes also called the weather-resistive barrier, this layer of any wall assembly is the material interior to the wall cladding that forms a secondary drainage plane for liquid water that makes it past the cladding. This layer can be building paper, housewrap, or even a fluid-applied material.. A smart vapor barrier is located on the interior of the wall framing. This is a polyamide membrane with a variable permeance rating to allow the wall to dry to the interior.
The ground floor slab sits on a 4-inch layer of EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest. insulation, which also wraps around and under the perimeter and interior footings. Type II EPS is used under the slab and at the sides of the footings; however, Type IX EPS is used under the footings for its higher bearing capacity.
Owner: REACH Community Development
Development support: Housing Development Center
Schematic design: William Wilson Architects
Architect of record: Ankrom Moisan Architects
General contractor: Walsh Construction Company
Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. consultant: Green Hammer
Structural design: Stonewood Structural Engineers
Mechanical system design: PAE Consulting Engineers
PHIUS+ rater: Earth Advantage
A low-slope roof insulated with 12 inches of polyiso
Capping the building is a prefabricated wood truss roof with 12 inches of polyisocyanurate insulation and a fully adhered single-ply roof membrane. A self-adhered rubberized asphalt membrane is installed over the plywood roof sheathing, serving as the vapor barrier at the roof assembly (and also functioning as a temporary roof during construction).
All apartments have decks or patio spaces. The decks help to shade the living room windows while providing more usable living space. Horizontal “deck extensions” and eyebrows, both of which were conceived of as design elements that help give the building character, further provide shading at bedroom windows (see Images #2 and #4, below).
Critical details for thermal and air barrier continuity have been identified at the footings, windows and doors, parapets, decks/eyebrows, and interfaces between the conditioned (Passivhaus) and non-conditioned zones. We will address these details in subsequent reports.
Windows from a local manufacturer
A key concern of all team members has been the availability of the specialized products needed to achieve Passivhaus certification, as well as the track record of these products. The U.S. marketplace for products that provide Passivhaus levels of performance is still in the early stages of development. Additionally, the design, construction, and operation of buildings are complex enterprises that entail numerous risks — including product reliability — and this becomes an important consideration in the design of any project.
The window and door selection process has been particularly rigorous. The team researched window options extensively, looking at products manufactured in the Pacific Northwest as well as several European products. Based on early scoping and pricing, the European products offered a higher level of performance at a lower estimated cost.
With 322 high-performance windows and balcony doors going into the project, the team did not feel comfortable specifying overseas suppliers. The team decided to specify locally produced windows from manufacturers with established track records for delivering high quality windows in a reliable manner on relatively large projects. We selected Euroline windows; that company demonstrated the best balance of performance and cost.
The federal funds used to help finance the project also added accessibility requirements above and beyond the typical requirements of the Americans with Disabilities Act (ADA). This made finding commercial-grade doors with a good air seal at the sill threshold quite challenging. At the doors between the interior (conditioned) Passivhaus and the non-conditioned zones, a 20-minute fire rating was also needed on top of the long list of other performance and accessibility criteria.
The team had a difficult time sourcing products that fully met all the criteria. Ultimately it was agreed to use a custom-fabricated insulated wood door with a drop-down seal at these locations, with plans to test the quality of the door seals to ensure adequate airtightness performance.
Space heating with heat pumps and electric-resistance heaters
The building will be served by three rooftop mechanical penthouses housing HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. equipment (see Image #5, below). Each penthouse will serve a “pod” of 18 to 20 apartments and a portion of the common areas. Rather than designing a fully centralized system, or a decentralized system with individual HVAC units in each apartment, the pod design is an approach that provides a high degree of efficiency while simplifying distribution and likely cutting down on maintenance needs.
Approximately 90% of the space heating demand will be met by heat pumps delivering space heat through the ventilation system, while wall-mounted electric resistance cove heaters in the apartments will fulfill the remaining 10% (see Image #8, below).
Selection of the heat-recovery ventilation(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. equipment required a similar amount of scrutiny as the window selection (see Image #9, below). Products offered by European manufacturers were evaluated and compared with those offered by North American manufacturers. This was a challenging process as inconsistencies between the different testing standards made it difficult to compare the performance of one ERV or HRV to another.
Ultimately, the team chose to use equipment from the Loren Cook Company — a North American manufacturer — due in part to cost considerations, but also based to a significant degree on the mechanical contractor’s prior experience with that manufacturer’s products.
Gas boilers provide domestic hot water
Domestic hot water is provided by a centralized system using two high-efficiency gas boilers. Hot water distribution trunks are routed through the floor/ceiling assembly above each corridor and are lined with heat trace tape in lieu of using a continuously re-circulating system.
To mitigate the risk of freezing at the non-conditioned zones of the building, plumbing is located within the cavities of the insulated Passivhaus walls. In future reports, we will discuss more details of the design of the mechanical, electrical, and plumbing systems.
Construction has started
In 2011, REACH selected Walsh Construction Company as the general contractor for the project. We’ve been at the table with REACH and the design team from project inception, working together in a highly collaborative effort to help put the project together. Construction began in June 2014, and a great deal has happened at the site since then.
The project is scheduled for completion in May 2015. Over the next six months, we plan to share stories of the construction, including successes as well as some of the challenges we’ve encountered along the way.
Mike Steffen is a builder, architect, and educator committed to making better buildings. He is vice president and general manager of Walsh Construction Company in Portland, Oregon.
- Image #1: Walsh Construction Company
- Images #2 and #4: William Wilson Architects
- Images #3, #5, #6, and #7: Ankrom Moisan Architects
- Images #8 and #9: PAE Consulting Engineers
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