LEED BD+C: Homes v3 - LEED 2008
Oak Street Lofts
LEED Platinum 2012
Goals and motivations
What were the top overarching goals and objectives?
One goal was to achieve long term financial sustainability for the development. By reducing energy use in the building, the project could more easily meet the very strict operating budget requirements of the Maine State Housing Authority.
The top three goals of the sustainability consultant were to reduce petroleum based fuel use through load reduction, reduced air infiltration to help energy efficiency and achieve the best quality indoor air.
The team focused on the building envelope as its primary means of reducing the heating load in our cold climate. We knew that Maine State Housing has a solar thermal domestic hot water pre-heat requirement, but did not expect to have any other renewable energy sources. Solar thermal was installed. Solar photovoltaic was not feasible mainly due to the taller buildings shading Oak Street Lofts.
Photo by Greg Payne
The envelope included wood framing, rigid foam insulation and cellulose dense pack in exterior walls. Blue Skin vapor permeable air and water barrier was used outside of the sheathing and integrated into the window flashing. Whole building air infiltration was extremely low and unit-to-unit compartmentalization met the LEED for Home Mid-Rise requirements.
What were the most notable strategies used to earn LEED credits?
Location was one of the most notable strategies that the developer used to earn LEED credits. The project is located in downtown Portland Maine in the Arts District across Congress Street from the Maine College of Art.
Linking the project to the art college helped the project have a following from the local artist community giving it an identity. The project received exemplary performance for both its proximity to dozens of community amenities as well as to hundreds of weekday public transit rides.
Photo by Jay Waterman
The interior of one of the studio spaces designed to give artists a comfortable working environment.
Energy efficiency was the major strategy for earning LEED points. City funding dictated that LEED Silver was a requirement, but the team targeted Platinum from the start. Another requirement was meeting the 2030 Challenge, which equated to roughly a 40% improvement over ASHRAE 90.1 2004. High efficiency heating system, solar hot water, heat recovery ventilation and an extremely well insulated and air sealed envelope allowed us to achieve this goal.
The artists have a work space with tables and work benches with lots of natural light. Even with some artist paints or other materials that might pose an air quality issue, the use of MERV 13 filtration in the building ensured good indoor air quality.
The total area of the building is 29,370 square feet, including 14,274 square feet of residential space which is highly insulated with a tight thermal envelope. With 5 ½" of cellulose wall insulation and double glazed, argon-filled windows equipped with low-emissivity coating, the walls achieve an average R-21 value rating. Exterior sheathing is sealed with a vapor-permeable air barrier which helps the building achieve an outstanding 0.13 CFM50/s.f. air tightness rating. Unit-to-unit air sealing measures ensure that even within the building, air is not uncontrollably transferred. The roof achieves an R-49 minimum and is clad with low-albedo roofing to reduce heat gain and minimize contributions to the city's urban heat island effect. The elevated first floor achieves R-30 through use of closed cell foam insulation combined with blown cellulose. On-grade floors are isolated from sub-soils with a continuous R-10 barrier of rigid foam board.
The tightly controlled building envelope is balanced by an energy efficient indoor air management system. Energy Recovery Ventilators (ERVs) provide fresh ventilation air that exceeds the minimum requirement by more than 30% while consuming less energy than a traditional ventilation system would consume at the code minimum ventilation rates. The "total energy" wheels in the Energy Recovery Ventilation's provide preconditioned air in the summer and space neutral air in the winter by recovering 76% of the energy in the exhaust air stream and transferring it to the supply air stream.
High-efficiency on-site laundry appliances compliment the low-flow water fixtures provided. Very low-flow plumbing fixtures include 1.28gpf water closets, 0.5gpm bathroom lavatory faucets and 1.5gpm shower heads. A solar pre-heat system for domestic hot water includes twelve (12) flat plate solar collectors. This system is capable of providing up to 60% of the estimated annual domestic hot water usage and up to 85% of the estimated domestic hot water usage during the summer months.
Aside from LEED certification, what do you consider key project successes?
The project provides a clean and welcoming home to many artists who otherwise might not be able to afford descent housing. The studio spaces and gallery allow works to be developed and displayed close to home, and encourages collaboration, imagination and creation of art. This building is a key piece to Portland's art community and the art gallery has quickly become a monthly stop on the city's First Friday's art walks.
What one thing saved you or the project team the most time, money, or helped avoid an obstacle during the LEED process? What one thing cost you the most?
Ensuring we had a very motivated contractor as the project manager made for a smooth LEED certification process saving time and money. An extensive pre-construction meeting to discuss the LEED requirements as well as documentation tracking tools with all design team members and as many subcontractors as possible was key to getting everyone on the same page. Regular discussions about LEED occurred throughout construction. When there were challenges along the way, such as compartmentalization testing and inspection for air sealing, the project manager was very helpful in resolving those issues.
The architect created a drawing in the construction documents set that was a LEED matrix of all required credits on what specification section they related to. If there was a specific material requirement or a submittal expected from the contractor, they could see all these requirements on one sheet within the drawing set. In this way all credits were accounted for and the contractor's credit responsibilities were highlighted.
Compartmentalization was a challenge that had to be re-visited after the first blower door test. The contractor stepped up and fixed a few penetration areas that had been overlooked. It is extremely important that all subs are aware of the compartmentalization goal for the LEED for Homes Mid-Rise project.
Photo by Greg Payne
The Oak St. project team learned a lot about what it takes to properly compartmentalize units. The LEED Mid-Rise program required all units to meet an air leakage standard of 7.0 Air Changes per Hour 50 (ACH50) or less. After completing initial testing on units that were near completion it became clear to us that we were missing the mark for the prerequisite. At this point, late in the game, we did not have the option to address leakage prior to Sheetrock, we needed to seal any and all leaks we were able to find in order to pass. The project team, including the site supervisor and a team of air sealers, gathered in a corner unit while a blower door test was conducted. All points of leakage were detected and fixed for a passing score. We collectively moved to the next (interior) unit and repeated the same effort. The people air-sealing now knew what to look for, and they moved through every unit sealing all gaps and cracks. Because of this experience we learned an invaluable lesson in planning for future projects.
In new projects, we now hold an air-sealing meeting very early with the project team and foremen from all major subs to address key air-sealing details and discuss who has ownership over each piece.
The units are continually inspected throughout the process through an 'air-sealing' lens, and blower door tests are performed early on to learn where leaks are still coming from.The foremen are included in the preliminary blower door testing. This helps set them up for success so they understand how important it is to not miss anything and see first-hand where the problem areas are.
Through compartmentalization testing we have learned:
- Corner units tend to perform better than interior units due to two well air-sealed and insulated exterior walls- as opposed to just one as the interior units do.
- All sealants shrink- and even more so with significant temperature fluctuation.
- Sprinkler heads are not designed to be air tight against drywall.
What was the value of applying LEED to this project?
I went to the ribbon cutting and heard one of the residents speak about her experience living in the building. She was an artist and has struggled with mental illness. The Oak Street Lofts building has given her a sense of stability that she had not had in the past and the fact that it was LEED certified meant a huge amount to her. Many low-income residents have lived in sub-standard conditions most of their lives. To move into a building where the developer actually cared about the indoor air quality, and the health of the tenants, appeared to be a great emotional boost for this woman.
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