Dedicated to growing the urban forest, Tree Pittsburgh wanted a sustainable headquarters that gives employees and volunteers easy access to the 100,000 trees they nurture and plant each year. Sited on a former steel mill above the Allegheny River, the simple, open building is comprised of nine double height modules, prefabricated in nearby Clarion, PA. Using prefabricated modules reduces on-site construction waste and creates a tight thermal seal for the building.

The modules sit lightly on the land, anchored by foundation piles that compress, rather than displace existing soil. Strategically placed doors and windows capture views and bring in light. A long, linear porch serves as an outdoor space for staff to relax and for guests to gather at an event. Photovoltaic solar panels on the south-facing roof will provide their power, helping Tree Pittsburgh achieve net zero energy. A 3,000-gallon temperature-controlled water tank provides the campus with its potable water; sensors alert staff when supply is low.

Sustainability. The limited access to utilities and contaminated brownfield soil became project drivers for sustainability. A 6” layer of clean fill was added throughout the site and the helical pier foundation system limits soil disturbance. Prefabrication helped limit construction waste and led to a thermally sealed building assembled in a controlled environment. Given the funding streams, the design team balanced building energy use with the photovoltaic array production capacity, size and cost. The roof material, building massing and orientation, and thermal envelope were all carefully designed to maximize impact of the array and minimize energy use. Utilization of natural and renewable materials, triple pane glazing, operable windows, low flow plumbing fixtures, high efficiency lighting, and stormwater capture make it one of the most environmentally responsible buildings in the region.

Residential scale building systems act as demonstration tools for visitors. Heating and cooling of partially occupied spaces is provided by on-demand units and all roof rainwater is collected in barrels for irrigation. Supply water through a public utility was not available, so all potable water is delivered to a storage tank that employs a charcoal filter and ultraviolet system to further clean the water. If state regulations change, the system could be adapted to feed the supply water tank with collected rainwater. The impact the project can be felt at an urban scale: a once blighted industrial site is now filled with thousands of trees that improve air quality and a building that educates visitors about sustainable strategies in their homes.