The Minneapolis Federal Building was built in 1913 and is listed on the National Register of Historic Places (NRHP). The building, set in a bustling downtown area, was fully occupied during construction. Execution of the work required extensive planning, coordination, and permitting for street and sidewalk closures. Overhead protection and covered walkways were installed around the building so building occupants, visitors, and public pedestrian traffic would not be impacted. A secure stair tower and scaffolding was erected for workers to safely access the multiple roof levels, and to perform the difficult work at the perimeter of this steep-slope copper roof.

The primary scope of work was to replace the lead coated cooper standing seam metal roof with a new zinc coated copper system, while preserving the historical and architectural integrity of the site. Included was the replacement of skyward facing soft caulk joints in the adjacent granite masonry. An extensive permanent perimeter fall protection system was also designed, custom fabricated, and installed as part of this project.

The existing roof assembly was robust, consisting of mutlple layers of framing, insulation, vapor barriers, underlayment, and copper panels. All layers were removed down to the original structural concrete deck. New wood blocking was added followed by installation of 1.5” rigid insulation board, which was set between the blocking, new 23/32” plywood decking was fastened to the wood blocking, and a self-adhered butyl laminated polyethylene membrane was installed as a waterproof underlayment. New shop fabricated zinc coated copper panels, caps, hip, valley, fascia, and edge metal were installed. The metal panel profiles, seam types, hip/valley, and all associated flashing work were all formed to match the original profiles of each respective detail, which involved a great deal of soldering. Due to the difficulty level of this work, the highly visable profile, and the historic value of this structure, ONeill built mock-ups and conducted in-field soldering testing of every worker prior to permitting them to complete any contract work. Upon competion of the roof system, 1,200 custom copper snow guards were soldered to the new panels in a layout pattern engineered specifically to the type, size, and slope of the roof and designed to withstand the locations winter conditions.

The joints of the rising granite walls adjacent to the copper roof were cut out, cleaned, and resealed. Galvanized fall protection davits and single-point anchors were engineered, fabricated off-site, and nstalled on the built-up roof directly above the new copper roof.. The existing built-up roof system was removed down to the concrete deck. The concrete was core drilled at very precise locations at the sides of the existing structural beams below the concrete. Preparing for structural attachment of the new davits to the building frame required extreme precision due to the irregularities and inconsistent dimensions and spacing of every structural member. The demolished roofing was restored using the same material as the existing built -up roofing system to make the davits watertight.