PODIUMS—AN ALL-WOOD SOLUTION

Although a podium structure typically refers to wood-frame construction over concrete, a handful of designers have lowered their costs even further by designing the podium in wood.

“When determining the cost of a structure, there are a lot variables, including most notably time, materials and labor,” said Karyn Beebe, P.E., of APA. “Using wood instead of concrete lowers the mass of the building, which results in more economical podium shear walls and foundations. Using the same material for the entire structure may also mean lower design costs, and the construction team experiences savings in the form of fewer trades on site, which means less mobilization time, greater efficiency because framing is repeated on all of the levels, easier field modifications, and a faster schedule.”

Architect Dan Withee, AIA, LEED AP, of Withee Malcolm Architects designed an 85-unit wood podium project in San Diego. He estimated that a concrete podium can cost $15,000 per parking space compared to $9,500 for an all-wood solution.⁶

MIXED-USE PODIUM BUILDING

Project: Parkside mixed-use project, a combination of the Parkside affordable housing project (77 apartment units) and East Village Community Church (11,000-square-foot sanctuary and related facilities)
Location: San Diego, California
Architect: Benson & Bohl Architects, Inc.
Code consultant: CHURCHILL ENGINEERING, INC.
Residential (five levels of wood-frame construction): 67,109 square feet
Church (one level plus mezzanine): 12,209 square feet
Parking garage (three levels): 48,213 square feet
Total area of building: 127,531 square feet
Type of construction: Type IIIA platform wood construction over a Type 1A concrete podium
Year of completion: 2010

Parkside, a $20-million LEED Platinum-certified project, demonstrates the use of code provisions to increase height and area. Installing NFPA 13-compliant sprinklers in the wood-frame portion permitted a height increase of one story to a total height of 85 feet with five stories, explains building code and life-safety consultant James E. Churchill, P.E., president of CHURCHILL ENGINEERING, INC. An additional 11,040 square feet in the wood portion of the building was permitted through the frontage provision (IBC 506.2), which allows an increase in building area if the building fronts on a public way or open space. (Unlike the IBC, the California Building Code [CBC] permits an increase in building area based on frontage, but not on the use of sprinklers if that provision has already been employed to gain an additional story.)

The concrete podium provides a three-hour fire-resistant horizontal assembly which separates the wood stories above from the stories below, allowing the wood building and the podium to be treated as separate buildings for the purposes of determining area limitations, continuity of fire walls, number of stories and type of construction.

Two vertical three-hour fire walls extend from the first floor level above the podium to the roof level, separating the residential portion of the building into three separate buildings. Without the special provisions for horizontal assemblies in Section 509.2 (2009 IBC), which permit portions of structures to be treated as separate buildings, the fire walls would have had to run from the foundation level to the roof level, dividing the parking garages, thus making the building program impossible to deliver.