Thomas J. Leidigh, 94, of Southampton, a founding partner of the Philadelphia engineering firm Keast & Hood Co., died Sunday, Feb. 3, of complications from Parkinson’s disease at ACTS Southampton Estates, a senior facility in Bucks County.

A practical problem-solver, Mr. Leidigh devised solutions to complex design issues in his work at Keast & Hood. He collaborated with the noted architect Louis I. Kahn on many projects and completed hospital, government, and academic buildings such as the Richards Medical Research Laboratories in West Philadelphia. He also worked on a 15-year renovation of City Hall and the statue of William Penn atop it.

Born in Philadelphia, Mr. Leidigh grew up in Fox Chase and Quakertown. He was a 1942 graduate of Central High School and a 1949 graduate of what is now Drexel University. His major was civil engineering.

Starting in 1943, during World War II, he served in France and Germany as an Army draftsman with the 406th Infantry Regiment, 102nd Infantry Division. He was honorably discharged in 1946 with the rank of technician fifth grade.

Mr. Leidigh worked briefly as a civil engineer for the Baltimore & Ohio Railroad in Pittsburgh and in Clarksburg, W.Va., before returning to Philadelphia.

In 1953, Mr. Leidigh and four others founded the structural engineering firm Keast & Hood. When two of the partners died in a plane crash while returning from a job site in 1963, and a third man not on the plane died of natural causes, Mr. Leidigh and Nick Gianopulos were left to rebuild the company.

They invited Carl Baumert to join them, and the triumvirate led the firm from the 1960s through the mid-1990s. Mr. Leidigh retired in 2007. With his death, all the founding partners are gone.

Thomas J. Normile, an engineer who joined the firm in 1996 and is now a partner, called Mr. Leidigh “the unsung hero of Keast & Hood.”

“Tom was definitely the quiet, brilliant mind behind the scenes,” he said. “Nick was the public face of the firm. Tom was the guy who was making it work. Like so many partnerships, there are front guys and back guys. Tom was the engineer, the tinkerer, working the numbers and figuring out the details.”

Normile said Mr. Leidigh “had an uncanny ability to dissect engineering problems into their basic elements, which made solutions so much easier.”

Keast & Hood rose to prominence through its collaboration with Kahn, whose buildings were characterized by powerful, massive forms that often reflected the uses within.

One such building, completed in 1965, was the Richards lab on the University of Pennsylvania campus, in which utilitarian functions such as stairs and pipes were set off from offices and laboratories in four towers.

“That was the period during which the firm became the go-to engineers for a discerning level of architecture,” Normile said. “Kahn is the name you revere.”

In the 1980s and 1990s, the firm specialized in historic preservation. One high-profile project was City Hall, which needed cleaning, marble restoration, and repair for the Calder statue of Penn atop the building.

From left, Thomas J. Leidigh, Carl Baumert, and Nicholas Gianopulos, partners in Keast & Hood, atop William Penn's hat above Philadelphia City Hall in the 1980s.
Courtesy of Keast
From left, Thomas J. Leidigh, Carl Baumert, and Nicholas Gianopulos, partners in Keast & Hood, atop William Penn's hat above Philadelphia City Hall in the 1980s.

At one point, as a gag, the firm’s board of directors ascended to the platform around Penn’s hat to hold a meeting. A photo taken that day shows Mr. Leidigh and his partners wearing hard hats.

A willing mentor, he worked with future architects as an architectural department structural critic and lecturer at Temple University’s College of Engineering Technology.

He spent many summers in Ocean City, N.J. He was an active member and volunteer at Bustleton United Methodist Church, and a former president of the Engineers’ Club of Philadelphia.

His wife of 64 years, Jean MacMillan Leidigh, died in 2014 at age 89. A son, Thomas James Leidigh, also died earlier.

Mr. Leidigh is survived by sons Richard and Robert; three grandchildren; two great-grandchildren; two nephews; and a niece.

A memorial service will be held at 2:30 p.m. Sunday, Feb. 24, at Southampton Estates, 238 Street Rd., Southampton. Burial will be private.

Donations may be made to ACTS Samaritan Fund via, or the Michael J. Fox Foundation for Parkinson’s Research via‎.