The city of Seattle in 2011 began requiring new construction and major renovations over 5,000 square feet to meet LEED gold.
That same year, the city selected a design team to renovate the aging Fire Station 18 at 1521 N.W Market St. in Ballard. The station, originally built in 1974, is now the lead station for Battalion 4 serving northwest Seattle.
The project was initially limited to structural upgrades but expanded into a major renovation after a preliminary review found inefficient building systems approaching the ends of their serviceable lives, envelope components in need of replacement, and crew facilities that no longer met the operational demands of the fire department. With the increased scope, the renovation of Fire Station 18 sought to answer the question, “How lean could this 1970s-era energy hog become?”
Understanding the embodied energy value of existing buildings, the team embraced the existing site constraints, systems and assemblies. An integrated approach including the entire design team, owner and firefighters developed strategies to meet the functional, performance and operational challenges of the project. Two sustainable strategies emerged:
• Reduce: Use less new energy by installing high-efficiency building systems and minimizing energy loss through envelope.
These two strategies resulted in a renovated Fire Station 18 designed to operate at an Energy Use Intensity (energy used per square foot of building) of 51 kilo-British thermal units per square foot annually — 40 percent below the average of Seattle neighborhood fire stations.
To optimize the existing building, the design team analyzed its limitations and advantages.
The existing building’s primary structure consists of parallel masonry bearing walls running north-south, supporting floor and roof assemblies of glu-lam beams, wood decking, and concrete topping slabs or precast hollow-core concrete planks with concrete topping slabs.
While structural analysis showed the building required substantial intervention to achieve the required seismic performance level of “immediate occupancy,” the basic structure of the building had several desirable qualities.
First, the primary structure was clearly distinguished from space-defining partitions, allowing for easy identification and reconfiguration of the nonstructural partitions to accommodate the fire department’s changing programmatic needs. Further, the primary structure is composed of durable materials capable of standing up to the wear of an all-hours facility. So in spite of 40 years of service, it remained in relatively good repair.
Lastly, existing glu-lam beams and decking met the dimensional requirements of heavy timber construction, meaning the assemblies had some fire resistance rating.
Given these qualities, the decision to retain as much primary structure as possible was made early in the design process. In total, over 95 percent of the primary structure of the existing building was reused.
The first step in designing the building to consume less energy was to establish a baseline performance.
Working with an existing building provided two points of comparison. The station had a pre-project EUI of 82.3 in 2014.
For the second step, our team created an energy model showing the performance of a hypothetical version of the fire station constructed to the current requirements of the Seattle Commercial Energy Code. This model performed significantly better than the existing station — an EUI of 54.6.
Using the energy model to test the impact of specific design options, the team worked to improve performance beyond code requirements. Taking into account the unique operational requirements of the station, this analysis allowed the team to make strategic interventions to selected envelope components to yield the best building performance within the project budget.
In the end, a combination of increased roof insulation, replacement of leaky and poorly performing glazing, and selective insulation of existing exterior masonry walls provided the best results.
Another critical part in reducing energy consumption was to upgrade building systems. A large part of the improved building efficiency is due to the replacement of the existing gas-fired boiler used for heating and the window AC units used for cooling.
They were replaced with a high-efficiency, variable-refrigerant flow air-source heat pump. Individual fan coils in each of 17 building zones allow for simultaneous heating and cooling and greater control of thermal comfort. The ventilation system features heat recovery allowing up to 72 percent of waste heat in the exhaust air stream to be recaptured to preheat outside air.
Plumbing system upgrades included high-efficiency, gas-fired water heaters and low-flow fixtures throughout the station. Electrical and lighting systems improvements included the nearly exclusive use of LED fixtures, vacancy sensors and automatic daylight zonings.
The net result for the renovated station is an EUI of 51.0. This represents a 6.6 percent improvement over prescriptive code performance, a 37.8 percent improvement over the existing station, and a 40.7 percent improvement over the 2014 city average for neighborhood fire stations.
The improved efficiency combined with the retention of the embodied energy of the existing station demonstrated the effect that conventional sustainable strategies can have when rigorously applied to existing buildings.
Nelson Martelle is an associate at SHKS Architects, where he concentrates on complex renovations of existing buildings.
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