The Macallen Building is a 149-unit condominium that includes three levels of parking and a 20,000 square foot elevated green roof with a 17 degree slope. The residential portion of the building is a 218,000 square foot steel structure, consisting of a staggered truss system. This system provides the building with column-free units and reduced the need for column transfers at the parking-level drive lanes.
The floor-to-floor height in the residential levels is 11’-1” while the parking levels have varying heights. The building façades consist predominantly of insulated, operable windows and architectural metal panels and “fins”. The use of modern construction materials on the building’s exterior is both a response to its location in Boston’s trendy South End and a statement to the general public as to the forward thinking behind the building design as a whole.
The Macallen Building’s amenities include a pool on the green roof plaza area, a private gym for residents, over 30 different apartment layouts, and a screening room with stadium seating, an HDTV projection screen, surround sound, and a kitchen to cater the events held there.
In addition to its innovative architectural design, the Macallen Building is the first residential building in Boston to receive LEED certification, earning a LEED gold rating. All mechanical, electrical, and plumbing systems and fixtures are energy and environmentally efficient, including the Central Plant heating and cooling system and the award-winning Dophin water cooling system. Each year, the Macallen building saves over 600,000 gallons of water and uses 30% less electricity than the average, similarly sized building.
The exterior building walls on the residential levels are curtain walls with the primary back-up structure consisting of steel framing. The finish materials vary along the different building façades.
The east elevation consists of 12” Norman bricks in soldier courses. This system is backed by a 2-1/2” air space and 2” extruded polystyrene insulation panels (with an R-value of 12.5) over a self-adhered, rubberized-asphalt air and vapor barrier on Densglass exterior sheathing.
The north and south elevations are finished with 14’-4” x 2’-8” composite metal panels backed by a hook and pin rain screen system. The composite system rests over 2” extruded polystyrene insulation panels (with an R-value of 12.5) over a self-adhered, rubberized-asphalt air and vapor barrier on Densglass exterior sheathing. This is backed by an additional layer of batt insulation (thickness and material vary depending on location) with a gypsum wallboard interior finish supported by 6” light-gage metal framing.
Vertical stainless steel fins cover the west elevation and the parking levels on all building façades. The fins are backed only by the adjacent structural system or insulated windows.
The green roofs rest above layers of drainage mat, fully-adhered PVC waterproofing membrane, and 3” extruded polystyrene insulation panels. Regions outside of the planted roof areas are covered with unitized, pedestal-supported roof pavers. This arrangement is supported by a sloped steel deck and cast-in-place concrete composite system ranging from 5”-7” thick.
The other roofing system found on the Macallen Building is a PVC membrane roof. The surface layer consists of a single layer, 80-millimeter thick PVC membrane with Energy Smart “White” flashing. Beneath this lies layers of glass fiber mat exterior gypsum board and extruded polystyrene insulation panels (with varying thicknesses to accommodate drainage and an R-value of no less than 20.0). This roofing type is also supported by a steel deck and cast-in-place concrete composite system.
Structural System
There are two primary structural systems present in the Macallen Building, separated by the two basic building functions, parking and residential areas. The first three building levels are cast-in-place concrete. The vertical supporting elements on these floors are reinforced square columns with diameters ranging from 1’0”-3’0” and bay spacing at 36’0” in the east-west direction. The floor system on the parking levels is a 1’0” thick, self-supporting two-way concrete slab with thickened areas poured at 1’4”. The lateral resistance system on these floors consists of a series of cast-in-place reinforced concrete shear walls that are 1’6” thick and spaced at 72’0” on center. These shear walls resist lateral forces in the north-south direction. Lateral forces in the east-west direction on these floors are resisted by concrete moment frames.
The second system, which is located on the 11 residential floors above the parking levels, consists of steel framing with composite slab floors and an 11’1” floor-to-floor height. The columns are a combination of W14 and rectangular HSS steel members. The floor system on these levels is a composite steel deck and cast-in-place concrete system. The steel deck is 2” deep with 5” of reinforced concrete placed above the deck ridges and ¾” diameter shear studs completing the composite floor. The lateral resistance system on the residential levels is achieved through a staggered steel truss system, which resists lateral forces in the north-south direction, and moment connections, which resist lateral forces in the east-west direction. The horizontal members of the steel trusses are W14 shapes with HSS members running in between them, acting as web members.
The foundation is a 1’2”-1’6” thick slab on grade with piles. The piles are prestressed, precast concrete piles with minimum widths of 1’2”. The design load on each pile is 120 tons. The pile caps are reinforced concrete with thicknesses ranging from 3’0”-4’6”.
Fire Protection
The building is fully sprinklered with automatic sprinklers. A dry pipe system protects the parking levels and a wet pipe system protects the residential floors. A manual/automatic smoke and fire alarm system are also in place to protect the residents in case of a fire on or near the building premises.
Building Transportation
The main entrance and lobby are located on the west end of the north building elevation. There are two elevators and one of two main staircases in this area. One elevator has a 3,500 lb. capacity and the other a 4,000 lb. capacity and they run on 26 and 29 horsepower hydro pump motors, respectively. Each moves at 350 feet/minute. The other main building staircase is located on the east side of the building. Additional staircases exist on the parking levels for egress convenience.
Telecommunications
Three main lines run into the building underground in 4” conduit, one from Comcast which provides cable television and two from Verizon which provide telephone and internet to the building. The lines are stacked vertically for efficiency and run to each individual apartment unit. Tenants are responsible for installing individual communication systems and devices.
Lighting
Primary hallway lighting is provided by fluorescent wall sconces. The apartments are lit predominantly by 18W/120V recessed compact fluorescent downlights or 50W/12V downlights with baffles or reflectors. Also used in residential portions of the building are 20W/120V linear fluorescent strips with T8 lamps. Extensive natural lighting in residential areas is facilitated by both the building’s long, narrow design and relative height of apartments to surrounding structures. The parking garages are lit with 70-200W/120V surface-mounted metal halide lamps.
Electrical
Each floor is controlled by 400A circuit breakers which are fed by 1000-2000A bus ducts which run vertically through the building. The building also uses 208Y/120V, 125A panelboards on each floor. Primary power is brought into a 750kVA transformer, which steps down to 208Y/120V. Emergency power is provided by a 600kW diesel generator.
HVAC
The residential units are heard and cooled with 208V heat pumps with compressors. There are 323 of these pumps stacked vertically throughout the building. Energy recovery units condition fresh air in to the apartments and corridors using the air temperature from building exhaust systems. Domestic water is heated by steam provided by the Trigen Energy Corporation. This steam condensate system utilizes shell and tube heat exchangers.
Construction Management
The project delivery method was fast-track construction with a guaranteed maximum price contract. The job broke ground on July 25, 2005 and construction completed on July 31, 2007. The site was excavated a maximum depth of 20 feet to the deepest point at Dorchester Avenue with piles going approximately 85 feet subgrade. Cast-in-place concrete work started on August 11, 2005. The parking-level framework concluded on December 19, 2005 and the steel erection began less than month afterward. The structural framing was topped off on May 25, 2006.
