|Adding planter boxes to the new patio creates a streetscape finish similar to the previous look.
Photos by Bill Ballas, Plath & Co.
Putting an addition on a San Francisco home often imposes immediate challenges, given the elevations and rises that are characteristic of the terrain. Other challenges made this project particularly unique: its historic registry listing (the home was built in 1895); a fragile sandstone veneer that could not be duplicated yet had to be echoed in the addition's cladding and towers rising four stories above the building site. Thoughtful and thorough solutions became the hallmark of the project's success.
The multigenerational family that lived in this mansion needed a garage to accommodate its vehicles, and the family wanted a backyard for congregating and entertaining. It also wanted to upgrade a small but deteriorating and slightly dilapidated cottage just adjacent to the main home to have a more pronounced relationship and traffic flow between the two buildings, creating more living space. The homeowners approached Plath & Co. to do the addition because the company had done three jobs for the family since it bought the home in the early 1990s. One seismic job brought the home up-to-date with current unreinforced masonry building (UMB) standards.
"This was an original building, a San Francisco landmark, a 19th century, close to 15,000 square foot brick mansion. And it's clad in sandstone, so you live under a lot of eyeballs keeping you on the straight and narrow," says Plath & Co. President Steve Plath, about the necessity to balance the standards of the historic registry board, zoning restrictions and building code requirements with the homeowners' needs and wants. "In finishing the street side of the garage, it was important that we didn't duplicate the main home. Even though it's a historic property, architecturally you had to be able to delineate the new from the old — but it had to be a comfortable transition."
After an intense and lengthy six-month excavation (which lowered the backyard by 12 to 15 feet to street-level), the project got a big break when an exploratory pit revealed that the foundation of the main home was deeper than needed and required no underpinning. But tiebacks — in this case, about 20 — would be necessary to ensure the more than 100-year-old foundation would accommodate downloading from the addition and would not rotate and be susceptible to side-to-side shifting, a real concern in "earthquake country," Plath says.
Once the foundation was fortified and the cottage and portico were properly shored, the 45- by 54-square-foot addition was built. It features a heated 10-car garage and patio deck, and the addition was clad in stucco that matched the color, shape and texture of the original sandstone. Four 11-ton concrete beams carry all of the loads for the deck.
A concrete basement was added to the wooden cottage. The cottage was then connected to the main house to allow interior access from the garage, which called for a cut in the almost 2-feet-thick structural, load-bearing rear wall just left of the existing portico, creating the 16-foot-wide, full height connecting span. The wall was reinforced with steel beams.
The total remodeled and addition space amounts to 5,000 square feet and took approximately 1½ years to complete.