building GREEN

Copy of WALSH Blog #2 November 2014

The Orchards at Orenco

Constructing A Model for Ultra Energy Efficient, Affordable Housing in the Pacific Northwest

The Orchards Team

To bring the Orchards vision to life, REACH assembled a team of Portland-based design, development and construction firms. Housing Development Center has provided development support and owner’s representative services. William Wilson Architects developed the schematic design, while Ankrom Moisan Architects completed the design and has served as Architect of Record. Walsh Construction Co. is the general contractor. Green Hammer has provided Passive House consulting services. PAE Consulting Engineers has provided design of the mechanical systems and Stonewood Design has served as structural engineer. A highly collaborative team effort amongst this group of seasoned, committed professionals resulted in an economical, constructable design that meets all the criteria for Passive House certification. PHIUS has been an outstanding partner to the Orchards team as we have worked through a number of issues unique to a larger, multi-unit residential project. The project was PHIUS+ pre-certified by PHIUS this past May just prior to the start of construction. Earth Advantage, also based in Portland, will serve as the PHIUS+ rater on the project.

Building Design

The building is laid out in an L-shaped form, with two wings of residential units and a “knuckle” of common spaces at the corner. Although in terms of energy efficient design, the building form is not optimal from an orientation or massing standpoint, the “L” shape – and the considerable amount of articulation of the building – were required to meet 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 Passive House envelope. These spaces require high ventilation rates, which would have resulted in large volumes of conditioned air being exhausted from the building had they been within the Passive House zone. 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 building structure consists of three story wood-framed construction on top of a slab-on-grade foundation. Typical enclosure walls have 2×10 framing with blown-in fiberglass cavity insulation in the stud cavities and 1-1/2” of rigid mineral wool exterior insulation. Mineral wool was chosen specifically due to its permeability and capacity to facilitate drying to the exterior as environmental conditions allow. Plywood exterior sheathing (with taped seams) serves as the primary air barrier at the enclosure walls. A mechanically-attached spun-bonded polyolefin sheet membrane, installed over the plywood sheathing, serves as the water-resistive barrier. The vapor barrier is located on the interior face of the wall framing. This is a polyamide membrane with variable perm rating to facilitate wall drying to the interior. The ground floor slab sits atop a 4” layer of EPS 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. Capping off the building structure is a prefabricated wood truss roof with 12” 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 temp roof during construction).

All apartments have decks or patio spaces. The decks help to shade the living room windows while providing more useable living space. Horizontal “deck extensions” and eyebrows, both of which were conceived of as design elements that help give the building articulation and character, further provide shading at bedroom windows. Critical details for thermal and air barrier continuity have been encountered at the footings, windows and doors, parapets, decks/eyebrows, and interfaces between the conditioned (Passive House) and non-conditioned zones. We will address these details in subsequent reports.

Material and Component Selection

A key concern of all team members has been the availability of the more specialized products needed to achieve Passive House certification, as well as the established track record of these products. The U.S. marketplace for products that provide Passive House 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 and looked at products available from local manufacturers (based in the Pacific Northwest) as well as several products manufactured in Europe. Based on early scoping and pricing exercises, the European products offered a higher level of performance, and at a lower estimated cost. However, the team collectively decided to move forward by specifying products produced locally by manufacturers with established track records for delivering high quality windows in a reliable manner on relatively large projects. With 322 high performance windows and balcony doors going into the project, the team did not feel comfortable specifying overseas suppliers.

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 occurring within the interior Passive House barrier interface between conditioned and 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 has 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.

Building Systems Overview

The building will be served by three rooftop mechanical penthouses, each one housing a set of HVAC equipment, and serving a “pod” of 18-20 apartments and a portion of the common areas. Rather than designing a fully centralized system, or a “decentralized” system with individual units in each apartment, the pod design is an alternate 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 through the ventilation system, while wall-mounted electric resistance cove heaters in the apartments will fulfill the remaining 10%.

Heat recovery ventilation equipment selection required a similar amount of scrutiny as window product selection, as 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/HRV to another. Ultimately, the team chose to use equipment from 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.

Domestic hot water is provided by a centralized system, utilizing 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 Passive House walls. In future reports, we will discuss more details of the design of the mechanical, electrical and plumbing systems.