Skip to main content
Cathedral of St. Paul
Cathedral of St. Paul
Cathedral of St. Paul
Cathedral of St. Paul
St. Paul
Completion Date
9,000 sq ft.
Project Type
Cathedral of St. Paul and Archdiocese
Roof Spec, Inc.
McGough Construction

When the Diocese of St. Paul and Minneapolis began its two-year, $35 million restoration of the Cathedral of St. Paul, the design parameters for the cathedral's roof areas were to achieve the absolute maximum design life possible. That's why Hydrotech's Monolithic Membrane 6125® was chosen to play an important role in this intensive historical preservation project.

St. Paul's was built in the early 1900s, designed in the Classical Renaissance style and adapted from the original plan of St. Peter's Basilica in Rome. After 86 years, its 175-foot tall copper dome and other roof areas needed complete restoration, including the lower transept roofs, which had been retrofitted repeatedly over the years due to ice falling from the dome and damaging the lower flat roofs.
According to Roof Spec, Inc.’s Senior Roof Consultant Terry Thone, the design team determined that a paver-ballasted PMR (Protected Membrane Roof) system would provide the optimum surface for these roof areas. "However, we needed the waterproofing to be extremely strong, flexible, and have a redundancy in the application - a ‘belt and suspenders’. To provide this, we chose Hydrotech's fabric reinforced MM6125®."
The highly viscous MM6125, applied to the cathedral's concrete decking at 215 mils, created a seamless reinforced membrane, forming a long-lasting, tenacious bond to the new substrate and conformed to any deck irregularities. MM6125 is self-healing and can withstand and perform in submersed water conditions. High quality Hydrotech architectural pavers now serve as the roofs' finished surface. Thone says that the team is confident that the new roofs will meet the project's stringent performance design criteria. "We have enough faith in this application that it will last as long as our new copper dome."