Walter James Rossiter Jr., born on December 7th, 1942, in Boston, Massachusetts, to Walter and Lorraine Rossiter, passed away peacefully on November 10th, 2025, surrounded by his loving family.

Walt was a devoted son, husband, father, brother, uncle, and friend whose warmth, integrity, and generosity touched everyone who knew him. He is survived by his beloved wife of 61 years, Marie Rossiter; his children, Paul Rossiter and wife Jenny Rossiter, and Anne Rossiter; and his three cherished grandchildren, Nick, Ben, and Ella. He is also survived by his siblings Robert Rossiter and Elaine Keeley and was predeceased by his brother Paul Rossiter.

A proud Bostonian, Walt graduated from Boston College High School in 1960, earning a Bachelors in Chemistry from Boston College in 1964 and his Ph.D. in Organic Chemistry from the University of California, Santa Barbara in 1968. These academic achievements marked the beginning of a remarkable career dedicated to advancing materials science and building research.

Walt spent more than 35 years as a research chemist at the National Institute of Standards and Technology (NIST), where he worked with distinction until his retirement in 2006. His expertise centered on the performance of roofing materials and systems, building materials, thermal insulations, and the in-situ analysis of lead in paint and dust.

Following his retirement, Walt established his own consulting business and continued sharing his deep technical knowledge through his work with the Roofing Consultants Institute (RCI, now IIBEC) until 2024. Over the course of his career, he authored numerous technical papers, chaired and contributed to multiple ASTM International subcommittees, and served as a respected leader in the field. Walt was a member of RCI staff and foundation, the International Council for Research and Innovation in Building and Construction (CIB), and the International Union of Laboratories and Experts in Construction Materials, Systems and Structures (RILEM). He also served as past chair of the joint CIB/RILEM Committee on Roofing Materials and Systems.

Beyond his professional accomplishments, Walt was a man who embraced life with curiosity and joy. He was an avid traveler, always eager to explore new places and cuisines—especially his beloved French food fostered from his 15 months Paris stay as a scientific exchange scientist. He had a deep appreciation for folk and country and western music, which filled his home with warmth and happiness. Walt loved both playing and watching sports and never missed a chance to cheer on his favorite Boston teams. He especially enjoyed time at Bethany Beach with his siblings and their families. He loved spending time with his kids and grandchildren and took great pride in their achievements. His love for them was unwavering, and the time he spent with them brought him his greatest joy.

He will be remembered for his brilliant mind, gentle spirit, and deep compassion. His legacy of curiosity, generosity, and integrity will continue to inspire all who had the privilege of knowing him.

A celebration of Walt’s life will be held at St. Paul’s Catholic Church, in Damascus, MD on November 21, 2025, with visitation at 10:00 a.m., followed by a mass at 11:00 a.m., with a reception to follow at Whiskey Creek Golf Club. 

In lieu of flowers, the family kindly requests that donations be made to any of the following: Boston College High School, Children’s National Hospital Foundation E11ASTRONG,  Dana Faber Cancer Institute, or  RCI-IIBEC Foundation Scholarship, all very meaningful organizations to Walt.

Online condolences may be shared with his family on our website at www.molesworthwilliams.com