LEED BD+C: Homes v1.0 pilot
LEED Gold 2008
* This profile has been peer-reviewed by a USGBC-selected team of technical experts.
Goals and successes
What were the top overarching goals and objectives?
Avesta had just moved its offices into the neighborhood where Pearl Place now sits and wanted to promote smart growth through this housing development. They also wanted to contribute to the neighborhood revitalization efforts and felt affordable, high-quality and high-performance housing would be a meaningful catalyst.
What were the motivations to pursue LEED certification and how did they influence the project?
Motivations for this project included policy requirements and related funding stipulations. The City of Portland has a green building ordinance that states that any building receiving funds from the City needs to complete LEED certification at the Silver level.
Aside from LEED certification, what do you consider key project successes?
Key successes include fitting successfully in the borderline of a very dense residential neighborhood, next to a run-down industrial area; smart growth; efficient use of site; and implementation of allowable heights for maximum allowable density in minimum possible of land use.
One of the most obvious successes was the location of Pearl Place. This was a brownfield site that complied with all state requirements for mitigation and now is a safe place for families to live. Pearl Place is also a smart growth location in downtown Portland with close proximity to public transit, car share programs, commuter ferries to the islands and the largest employment base in the state. The project was also the first housing project in the nation to be certified under the LEED for Homes Mid-Rise Pilot Program.
This was one of the earlier housing projects that really took a hard look at the importance of air sealing the thermal envelope. Painstaking detail was used to seal every exterior seam in the construction.
What were the most notable strategies used to earn LEED credits?
Notable strategies included selecting an infill site; outstanding community resources and access to public transportation; minimizing the disturbed area of the site; attaining an average housing density of greater than 20 units per acre; installing very high-efficient plumbing fixtures; exceeding ENERGY STAR for Homes requirements; and using high-recyclable interior finishes.
Air sealing and compartmentalization helped both energy efficiency and resident comfort. The blower door test results showed air leakage at 0.228 CFM50 per square foot, which was 9% lower (better) than MaineHousing’s requirement for building leakage. A heat recovery ventilation (HRV) system was used since the building was so well-sealed. Indoor air quality was of utmost importance in the design and construction of this building. The HRV system allowed for a constant flow of fresh air while saving energy used to heat those spaces.
What additional green strategies did not directly contribute to a LEED credit?
Additional strategies applied to this project that did not result in LEED credits included locating the buildings on the periphery of the site and using the existing slope; utilizing most of the site for traffic and community space; and efficient construction by using the natural terrain and adapting the building structure to it.
What unique strategies were applied specifically because of climate or region?
Portland, Maine experiences just a few weeks a year that are hot and humid enough to really demand air conditioning. Rather than provide air conditioning to each unit, which would be cost prohibitive, Pearl Place was designed to provide air conditioning in the common community area only. This allows for a comfortably conditioned community space for those few hot and humid weeks.
What products were most effective in helping to meet project goals?
Marvin “Integrity” fiberglass windows were used.
How was the integrative process applied and what was the greatest benefit gained?
One benefit of applying the integrative approach included coming up with an efficient building design on a very tight site location. It enabled us to coordinate the size of the building, available area for required parking, and green space. In addition, we could not have achieved the efficient mechanical and electrical systems we did without all parties being engaged throughout the process.
The greatest value of applying the integrative approach was the sense that this is replicable. Costs came in approximately the same with other multi-family affordable projects in the Portland area and other developers realized that green buildings do not have to cost more than typical buildings. Soft costs for certification and consultants are still a challenge as Maine State Housing Authority refuses to allow any sources other than developer fee go toward building certification.
Which building codes, zoning or regulatory requirements influenced decisions and how?
The City of Portland has a green building ordinance that states that any building receiving funds from the City needs to complete LEED certification at the Silver level.
When was energy modeling used and how effective was it?
Various mechanical options were studied during energy modeling and this process helped the project team to choose a system with the best payback. During the design phase, a forced air system was compared to a hydronic system. Typically, shifting the energy load from the fans (forced air) to the pumps (hydronic) helps reduce energy consumption and improve thermal comfort.
Cooling was taken out of the scope of the project as Maine summers are mild. Operable windows give individual units option to use natural ventilation to cool or use window air conditioning units. We narrowed our options to a hydronic heating system with a dedicated outdoor air unit for ventilation. By shifting to this type of system, the team was able to reduce the ductwork (less material cost) and also allow greater ceiling heights. Compared to our baseline forced air system, the capital cost of the hydronic system was negligible. Radiant floor was considered as an option but was cost-prohibitive.
Different insulation systems were studied – insulation systems that not only improve thermal resistance but also inhibit infiltration. Infiltration could be a significant load for the residential buildings in cold climates. In tandem with the analysis to optimize the thermal conductivity, dew point analysis was performed to prevent condensation within the structure. 6.25-inch dense pack cellulose insulation in the walls and eight-inch spray foam insulation in the roof were finalized.
The ventilation system used in the project is a dedicated outdoor air unit with heat recovery ventilator (ERV). ERVs typically save energy, but it's necessary to determine the magnitude of these savings because the savings from recovering the energy from the exhaust air could be balanced by additional static pressure the ventilation fan has to manage. Our study found significant savings from ERV and this has been incorporated in the design.
The energy modeling process was started in the early design development phase. The model was used to optimize insulation values for the envelope (walls, roof and windows). Additionally, various mechanical options were studied for choosing a system with the best payback. Actual data has not been gathered yet. We are in the process of gathering data and comparing with predicted energy usage.
What value did commissioning add?
Commissioning was very valuable. From the beginning of the design, the commissioning review helped with resolving different options offered by the engineers. During construction, the commissioning inspections helped secure another level of quality control, as well as testing all equipment at the end of construction.
Issues identified during commissioning included improper air sealing, improper duct sealing, incorrect low-flow device installation, incorrect setting of operating controls on boilers, space thermostats placed in wrong locations, and boiler exhaust and intake not installed in an ideal location. All of the deficiencies noted through the project were noted in site observation reports and made part of a corrective action list that was followed up on by the commissioning agent and the general contractor. Items that were part of the original design were corrected.
What were the most important long- and short-term value-add strategies and what returns on investment (ROI) have been experienced or anticipated?
Site selection with outstanding community resources and abundant access to public transportation was a key strategy. Landscape design and planting selection minimized water use and created a pleasant green space for residences in the urban location. High-efficient plumbing fixtures conserve water and lower operational costs. A high-efficient electrical system with ENERGY STAR-rated lighting fixtures and use of daylight and occupancy sensors cut down the electricity use and again lower operating costs.
A key piece of the ability of the project to pursue the LEED certification and some of the green building strategies was the awarding of the Green Communities grant. This paid for both hard construction costs of green features in the building, as well as LEED consultants. Portland charges fees for both water used and sewage flow from the building. Reduced flow and flush fixtures helped bring this cost down. Daylight in stair towers along with banked lighting, occupancy sensors and daylight sensors contributed to keeping lighting energy at a minimum. LED exit lighting and CFL or T8 ballasts in other lighting kept electric loads as low as possible.
Purchase of high-efficiency boilers was pursued in part due to the savings associated with a lower operating cost.
Beyond the project, what impacts have the LEED and green strategies had?
The project is a Low-Income Housing Tax Credit financed deal with approximately six additional sources of financing. It was being designed as the Maine State Housing Authority was creating some of the first green building standards for state-financed housing. The design discussions about Pearl Place helped inform and influence the new green building standards that are seen as some of strongest in the nation today.
Avesta has taken a lot of pride in the overall achievement of Pearl Place. This has given the organization confidence to continue to build high-performance green affordable housing.
What project challenges became important lessons learned?
We explored impervious pavement. At that time, it was fairly new in this climate and we did not have as much information on the long-term results, especially in winter conditions with use of salt and sand. Although after many discussions and research we decided against this product, the process was very informative and I would recommend addressing this in other projects.
With the wall insulation system, we had two different buildings, both wood frame but one that was five stories high. That had to be built with a fire-rated exterior wall and fire-treated lumber and so we could not use any foam insulation on the outboard of the sheathing. We explored options of using 2x8 framing or 2x6 with furring to add thickness for insulation. After cost analysis, we decided on the 2x6 with furring and used the spray cellulose insulation. For the three-story building, we decided to use two-inch rigid polyisocyanurate insulation on the outboard of sheathing and three inches of spray-on cellulose in the cavity, only to find out during construction that the wet-applied cellulose has to fill in the cavity completely or once dried, it will crumble and settle at the bottom of the wall. In order to add cellulose to full the six-inch cavity, we had to make sure that too much insulation would not compromise the dewpoint location to fall inside insulation. Once that was confirmed, we added cellulose in the cavity and still were able to maintain the rigid insulation on the outboard, which was the preferred solution. Adding furring, however, was not the best application on-site and was too labor intensive. After construction, we concluded that using 2x8 might have been a better option.
Avesta Housing chose to have one of the two buildings gain certification through the LEED for Homes Mid-Rise Program and the other building through the regular LEED for Homes program, each with separate energy modeling protocols. This was a challenge as we compared the scored energy points related to ASHRAE 90.1 with the scored energy points on the other building that received a HERS score. They did not match up even though the buildings were identical, but one had an additional floor. As a LEED for Homes Provider, I would now push for one rating system for both buildings.
The five-story building was wood-framed. Structurally, that building needed what seemed to be an excessive amount of lumber on the first floor, in particular. Budget constraints prevented the use of FSC-certified wood. Today, FSC wood is relatively less expensive and is more readily available, particularly for framing of buildings.
Underground parking resulted in thermal wicking from the steel columns to the floor above. This was overcome by making certain the correct thermal breaks were utilized, as well as making certain that the roof of underground parking areas was properly insulated and air-sealed. In addition, temperature-limiting thermostats proved to produce tenant complaints due to a historical expectation of tenant space temperatures. This was overcome by understanding more of what would be tenant concerns, which in turn allowed for better education of tenant expectations.
What key moments adjusted the project’s direction or outcomes?
The original design visual was to have a single loaded corridor that allowed for an "all eyes on the street" arrangement with patios and decks overlooking the neighborhood. We imagined tenants being able to watch their children play outside the development. However, this type of construction proved to be more expensive than the project budget would allow. We switched to a double-loaded corridor which is not the best for overall movement throughout the development, but did allow us to move forward. The double-loaded corridor was a more efficient way to design, requiring fewer staircases, hallways, doorways, etc.
How has this project influenced your approach to other projects?
Site use, ventilation strategies, material use, efficient plan layout of units and the building overall (which minimizes the use of mechanical and electrical infrastructure in the building) are all approaches I have used in projects that followed.
Pearl Place was the basis for the creation of standard specifications for green affordable housing projects that Avesta Housing developed, as well as a template for Fore Solutions to use on other affordable housing projects. Pearl Place helped Fore Solutions flesh out the business model for offering verification services for these types of large multi-family projects with tight budgets. Energy efficiency really helped to lower operational costs for the housing development. Avesta has gone on to implement energy efficiency measures in other affordable developments.
Every building tends to offer lessons that are carried over to subsequent projects. Many of the strategies that were used on Pearl Place are still being used today or have been enhanced. For example, the owner has maintained installations of high-efficiency HVAC equipment and is continuing to utilize low-flow water fixtures on other properties.
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