The number of required parking spaces was reduced by virtue of the building program and alternative transportation-friendly design. The building is virtually occupied in shifts as the 2nd floor office space closes just before the 1st floor restaurant opens for the evening. Because the two floors are technically never open or occupied at the same time, the required number of parking spaces was reduced by 50 percent. Cavenaugh notes, "Shared parking basically allowed a single-story building to become a 2-story job, which is infinitely better on all fronts – density, livability, efficiency, design, mass, et cetera". Bike parking and an alternative fuel source for electric vehicles reduced requirements by an additional 25 percent resulting in a parking lot less than half of the required original size. This reduced parking-related paving costs roughly 25% and increased the site’s total usable area. The parking lot is a "no fines" lot and has only 8 spaces (including one handicap), one for every 250 square feet of restaurant less the bicycle reduction allowance.
Three different program spaces separate the street from the parking lot and substantially temper its presence. A 6’ wide lushly planted native landscape strip divides the parking lot from the restaurant’s exterior dining patio that bustles with restaurant goers on warm, pleasant evenings. The patio spills out onto the sidewalk effectively creating three distinct uses to screen the parking lot from the street. The patio also has traffic-calming qualities. Cavenaugh qualitatively notes, "Passing drivers have a tendency to slow down when the patio is set up and people are dining outside."
All parking lot stormwater runoff is diverted to a manhole in the middle of the lot that contains a "sedimentation filter" which then leads to a dry well. The filtered runoff infiltrates the underlying, well-drained glacial moraine soils and promotes ground water recharge. This strategy allowed the previously connected site to be disconnected from the municipal stormwater system.
Daylight is the primary source of lighting in the second floor office space. The small size of the space and open floor plan made it possible to achieve this condition by glazing only two of the building’s four orientations. A combination of large fixed windows and smaller operable windows dominate the northern exposure and promote diffusion of indirect sunlight throughout most of the floor. An east-facing clerestory and French doors expose the remaining depths of the space effectively creating a two-direction daylighting scheme whose effectiveness is relatively uninhibited by diurnal and seasonal solar variation. The fixed and operable windows have SHGC and VLT ratings of .33 and .57, and .3 and .5 respectively. The clerestory is strategically painted white to promote reflection of daylight into the space. Individual task lighting and 35-watt light bulbs that decoratively hang just overhead from the rafters supplement the daylighting strategy.
Battens and marine-grade finished plywood siding give the building a poignant, yet warm, appearance. The walls and ceiling are insulated with polyisocyanurate insulation to a value of R-21 and R-30 respectively. The roof is covered in a high reflectance Energy Star®- compliant roofing system with a solar reflectance rating of 80% to further reduce undesirable heat gain and mitigate the building’s contribution to the urban heat island effect.
2nd Floor- Interior & Program
An integrated cooling design eliminated the need to install a mechanical cooling system in the building. First, the climate-responsive building envelope design reduces the amount of direct solar heat gain while strategically promoting indirect daylight penetration for daylighting (see envelope). Secondly, the massive concrete slab floor helps moderate extreme interior daytime temperatures by absorbing ambient heat throughout the day. The stored heat is released as temperatures drop during the night thus restoring the slab’s thermal storage capacity and preparing it for another day of heat load mitigation. A clerestory serves as the heat outlet and also enables daytime passive ventilation. The clerestory collects heat above the occupied space and, when its windows are opened in union with the perimeter doors or windows, the collected heat rises out of the building pulling in fresh air from the lower inlets. The result is what Cavenaugh refers to as a "30’ tall thermal chimney" and is critical to the building’s ability to "breathe" and remain cool.
Two electric air-to-air heat pumps with a 98% efficiency rating heat both floors of the building. The system works in the winter by simply displacing warm air from the outside to the inside of the building. Unlike a gas system, the five-ton units also provide some degree of cooling in the summer. Energy consultant Carol Gardner notes, "If a gas heating system was used instead of an air to air system, he (Cavenaugh) would have needed to install a separate cooling unit as well". The air to air system operates more efficiently than a gas system and, coupled with the other passive cooling measures, eliminated the need for a separate cooling unit. A small internal auxiliary heater is available to supplement heating needs during rare periods of extremely cold weather. Electric air-to-air heat pumps are particularly efficient in mild climates and can be the most inexpensive way to heat a small building or home.
1st Floor- Interior & Program
Although the 1st floor tenant did not do a LEED-rated tenant improvement, Cavenaugh points out that, "He loves that it’s a LEED building. His space was done in the same vein". Using the same contractor, the tenant installed no carpet or interior walls and has an efficiently small refrigerator and kitchen. By virtue of the size of the space, simple concept, and open design the restaurant is operationally efficient and has a positive impact on the greater neighborhood.
However, there are always tradeoffs as Shea illustrates, "The credits for alternative transportation were easy by virtue of the urban context while the credit for no off-site light pollution was pointless." General contractor JP Viellet points out, "There’s a credit for using environmentally friendly carpet, but we couldn’t get a point for not using any carpet at all!" Such discrepancies point to the importance of balancing context and personal objectives with LEED standards. In general, aspiring for LEED certification required the team to pay more attention to daylight and views, control of space, and energy use. Such attention to detail, in turn, heightened the design precision and subsequent performance of the building.
Instead of settling for a certified level of LEED certification the team decided to go for silver because it was "more challenging and gave the building more rigor". An energy modeling consultant, commissioner, and engineering team were hired to verify building conditions as required by LEED. Just as the unique nature of the project made some credits easy to earn, it also rendered others more challenging.
LEED Credit 7.1 for Thermal Comfort requires third party verification that the building meets the standards put forth in ASHRAE Standard 55. The standard’s current criteria require that temperature and humidity levels remain within a very narrow range in the building. The range assumes that the building is airtight and that indoor environmental conditions are controlled principally by a mechanical HVAC system. New revisions to the standard, however, have more flexible comfort criteria specific to naturally ventilated buildings and finding an engineering firm privy to this change was challenging. "One firm actually wouldn’t do it (sign off on the building). They weren’t aware of the change and didn’t think it met the standard under the old criteria," says Shea. Another firm was hired for approximately $2,000 to verify the building’s comfort and provide the appropriate documentation to earn the LEED credit for Thermal Comfort.
Basic commissioning was a challenge as well because the air to air HVAC system did not include a performance specification to guide the commissioning agent. Furthermore, the subcontractor was "ill-equipped" to provide commissioning services. Consultant Mike Shea notes, "It was a small project with a small contractor and even smaller subcontractors". LEED’s influence has been primarily felt in large-scale projects and associated development teams and, as a result, small-scale contractors have little experience in applying the green building rating system. This resulted in apprehension on the part of the subcontractor and substantial delays in the process. In the end, an HVAC engineering firm was hired to perform the basic commissioning after developing a commissioning plan.
An energy consultant was engaged to perform energy modeling and produce a report in support of LEED credit 3.1, Optimize Energy Performance. Her input informed decisions about selecting the most efficient and cost-effective HVAC system, which serves as one component of the building’s integrated heating and cooling strategy. Energy consultant Carol Gardner notes, "The heat pumps contribute a lot to the building’s efficiency." Gardner also selected the glazing shading coefficient for the project. Her report indicates that the building performs 41% better than ASHRAE/IESNA Standard 90.1-1999 and her services cost approximately $3,000. LEED consultant Mike Shea notes, "There were no extra costs for meeting the LEED energy performance credits, except for modeling."
A CO2 control exhaust system further reduces building energy consumption. Typically, exhaust fans that cover washrooms and other areas in buildings run continuously thus constantly consuming energy. The design team remedied this potential squandering of energy by installing a CO2 monitor that turns the fans on only when CO2 levels exceed 700 ppm. It also modulates outside air dampers under this same threshold thus reducing the need to excessively heat and cool the building as ambient air penetrates the building.
Keys to Success - Design:
- Affront the building to the street to engage pedestrians and calm traffic
- Reduce total parking area by providing alternative transportation amenities
- Analyze underlying soils and infiltrate all stormwater on-site
- Site, orient, and design the building to use daylight as the primary light source
- Insulate the building beyond code requirements
- Install high reflectance Energy Star® roofing
- Do not install permanent walls or ceilings
- Provide communal office amenities
- Provide a vertical air outlet and install operable windows to promote natural ventilation
- Specify a high efficiency air-to-air HVAC system
- Pour a highly massive concrete floor to mitigate temperature fluctuations
- Do not install carpet
- Lease space to tenant that shares a similar vision for the space
- Ensure that the entire project team is LEED savvy early on
- Hire an energy consultant to help select the most efficient heating and cooling system