Maine Gets Another Passive House Multifamily Project
The development team looked for ways to keep costs down while accelerating the construction schedule
On November 21, three days before Thanksgiving, developers plan to complete Bayside Anchor, a mixed-use apartment building in Portland, Maine, built to meet the 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. + 2015 standard on what amounts to a shoestring budget.
The 45-unit building, about one-third complete, is located in the city's Bayside neighborhood, a part of the city carved in half by a 1960s urban renewal project. It will contain mostly affordable one-bedroom apartments, plus a few two-bedroom and studio units. The ground floor also will house an office of the Portland Housing Authority, a Head Start program, and a police substation, making it a community hub and giving it its name, Bayside Anchor.
Behind the project are the Portland Housing Authority and Avesta Housing, a private non-profit developer of affordable housing. The $7.6 million project is being financed mainly with low-income housing tax credits through MaineHousing, a state housing agency. The project was designed by Kaplan Thompson Architects of Portland. Wright-Ryan, which earlier this year finished a Passive House multifamily in Brewer, Maine, is the general contractor.
Although construction started in January, Bayside Anchor has been in the works since 2013. That year it won a national competition, sponsored by Deutsche Bank, for innovative designs for affordable housing.
Finding ways to cut costs has never been far from the minds of its developers, and efforts have paid off. The building will come in at $142 a square foot, project architect Jesse Thompson told a group touring the building recently, "substantially less" than the norm for new Portland housing. At the same time, residents will be getting the benefits of Passive House construction: low energy bills, high indoor air quality, and a superinsulated building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. that will keep them comfortable.
"You've got affordability baked into the building forever," Thompson said.
Passive House, but no room for frills
Passive House construction necessarily includes more insulation than conventional buildings, high-quality windows, and careful air-sealing, all of which can easily drive up costs. To stay within strict budget guidelines, Bayside developers looked for ways to trim unnecessary building elements — and that started with parking. Arguing that area residents owned fewer vehicles than average, developers successfully petitioned the city to overlook parking-space requirements that normally would have applied. (The building sits on what was a parking lot).
The site is over a layer of marine clay, which is inherently weak. Designers worked to keep the building as light as possible, allowing it to rest on a floating concrete slab without the need to sink pilings for extra support.
Project architect Jesse Thompson ledLight-emitting diode. Illumination technology that produces light by running electrical current through a semiconductor diode. LED lamps are much longer lasting and much more energy efficient than incandescent lamps; unlike fluorescent lamps, LED lamps do not contain mercury and can be readily dimmed. a tour of the partially complete building in June, the last such tour on this year's passivhausMAINE schedule.
Interior finishes are simple: painted drywall, vinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). flooring, basic kitchen cabinets. Designers shrank interior hallways to bare minimums, and revisited building details repeatedly to look for potential savings.
"The building got simpler and simpler as we went along," Thompson said.
While he and others working on Bayside might have preferred a few more upscale finishes inside, it just wasn't going to happen with a minimal budget that had been set three years earlier. If kitchens got bargain cabinets with drawers that were stapled together, so be it. "Every dollar in there shows up very quickly," Thompson said. "There's no tolerance for glamorous here."
Designers did, however, manage to find enough money to keep vinyl siding off the building's exterior. Instead, it will get fiber-cement claddingMaterials used on the roof and walls to enclose a house, providing protection against weather. over a ventilated rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. gap.
On the construction side, Wright-Ryan recognized that the longer builders were on site, the higher construction costs would be. Its construction managers, drawing on their experience at the Brewer Passive House project, looked for ways to speed up the process. They divided the building into sections, each with its own set of deadlines, to improve efficiency. Exterior walls are panelized rather than built on site. Even small steps helped: So workers would not have to sort through stacks of drywall to find the right thickness for a particular application, Wright-Ryan simply specified 5/8-inch wallboard throughout the building.
If developers hit the November 21 completion date for the 38,500-square-foot building, it will mean a construction schedule of about 10 months. Many single-family homes, Thompson pointed out, take longer than that.
Double-stud walls, and nix the OSB
Exterior walls consist of a structural 2x6 wall and an inner 2x4 wall with a 1-inch gap between the two. Wall cavities will be insulated with dense-packed cellulose, with a layer of CertainTeed's MemBrain on the interior to control vapor and air movement.
Thompson said that plans call for 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. on the exterior of the building rather than oriented strand board because plywood is more durable and more weather-tolerant during construction. Seams between sheets of plywood are sealed, and the entire outer surface is treated with a liquid-applied 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., Defendair 200, a mostly silicone product made by Dow Corning.
When it came to windows, designers considered a range of products before settling on triple-glazed units with PVC frames made by Kohltech, a Canadian manufacturer. Passive House buildings often get European tilt-and-turn windows, but in this case designers chose a mix of casements and fixed-glass units, in part to meet requirements of the Department of Housing and Urban Development.
As Thompson explained, Bayside Anchor will be required to provide air conditioning to any tenant who can present proof of a medical need. By using outward-opening casements, a tenant could use an air conditioner that sits on the floor and vents through a plexiglass insert in the window opening, thus meeting the HUD requirement, without installing AC for the whole building or investing in ductless minisplit heat pumps.
Windows specs are the same throughout the building, with a solar heat gain coefficient(SHGC) The fraction of solar gain admitted through a window, expressed as a number between 0 and 1. of 0.40. The Kohltech units averaged about $30 per square foot.
Other building details:
Insulation. In addition to the dense-packed cellulose in the walls (about R-32), there are 8 inches of polyisoPolyisocyanurate foam is usually sold with aluminum foil facings. With an R-value of 6 to 6.5 per inch, it is the best insulator and most expensive of the three types of rigid foam. Foil-faced polyisocyanurate is almost impermeable to water vapor; a 1-in.-thick foil-faced board has a permeance of 0.05 perm. While polyisocyanurate was formerly manufactured using HCFCs as blowing agents, U.S. manufacturers have now switched to pentane. Pentane does not damage the earth’s ozone layer, although it may contribute to smog. rigid insulation on top of the roof deck (R-50), and 3 inches of sub-slab expanded polystyrene. There is no spray foam in the building other than what was used to seal the rim joists between floors.
Ventilation. Each floor has two RenewAire energy-recovery ventilators to supply each apartment with fresh air. The units, which operate continuously, are 75% efficient. Kitchens have recirculating hoods that are not vented to the outside.
Space heat. Each apartment is heated with strips of electric baseboard that cost a total of $30,000. The bill to heat the entire building is projected at about $5,000 a year, Thompson said.
Airtightness. Although the standard for the German Passivhaus standard is 0.6 air changes per hour at a pressure difference of 50 pascals (ach50), the PHIUS + 2015 standard uses a different metric: 0.05 cubic feet per minute per square foot of gross envelope area at 50 pascals. When this is translated to ach50, it becomes 0.37.
The PHIUS standard is ideal for multifamily projects
Insulation R-values may seem low for a Passive House project, but Thompson said that's because a large multifamily building has proportionally less outside wall area for a given volume than does a single-family house.
"People are used to seeing PHIUS + and Passivhaus single-family houses with very large R-values," he said. "Passivhaus was invented as a multifamily program in Europe. It was not a single-family construction program. The numbers work so well in multifamily. In Germany, the first Passivhaus was a townhouse, and the middle unit in a town house has two walls that face neighbors — they don't touch the outside air.
"You think of a middle floor apartment at Bayside Anchor and it's got one outside wall. It's 24 feet long and 8 feet tall," Thompson continued. "So, thermally, it's just incredibly easy because your ratio of house to walls is tiny."
Heat loss from the building is one-third through the enclosure, one-third from the ventilation equipment, and one-third though the windows, Thompson said. In a single-family house, the numbers are very different, with ventilation losses only 10% to 15% of the total.
As a result , the 75% efficiency for Bayside's ERVs is very important for overall building performance, especially with something like 2,000 to 2,500 cubic feet of air per minute moving through the building around the clock. With an ERVEnergy-recovery ventilator. The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV. that efficient, when it's 0°F outside, and 70°F inside, incoming air is in the mid-50s. It doesn't take much energy to boost that to the set point. On a 30°F day, incoming air is in the low 60s. "Very little heat is needed to bring it up to a good temperature," he said.
Need for housing is very strong
Jay Waterman, development director for the Portland Housing Authority, said that Bayside Anchor will be both a catalyst for more development and a hub for the community. The area was completely changed by construction of Franklin Arterial, a main thoroughfare linking Interstate-295 on the west side of town and upscale Old Port, with its shops and restaurants, on the east.
"It was small streets, a grid-patterned working-class neighborhood for many, many years, and then through urban renewal, Franklin cut a swath so the tourists could get over to the Old Port and people were displaced," Waterman said. "It became more of a service center and industrial and lower income neighborhood, and I would say it’s still on its way up.”
The demand for housing is strong in the Portland area. Bayside Anchor, while significant for the neighborhood, won't put much of a dent in it.
"Let's put it this way," Waterman said. "There is effectively a 0% vacancy rate in Portland right now and the city would like to have 2,000 more housing units built in the next four years. We're doing 45, so it’s a real drop in the bucket compared to the demand.”
- All photos: Scott Gibson