Roofing Earthquake Retrofitted Historic Building

OVERVIEW: Designated as a National Historic Place, this building in Petaluma’s Historic Commercial District was built in 1880 and features cast iron over brick construction with paneled and bracket frieze, rusticated quoins, and dropped shoulder arched clerestory windows.

EARTHQUAKE RETROFIT: Although this unreinforced masonry building survived the 1906 earthquake, a seismic retrofit was completed in 1990 by installing steel posts and bracing, which linked the horizontal diaphragms, floors, roof, and vertical walls together. The unreinforced masonry parapet was stabilized with diagonal steel braces fastened to the roof structural members.

PROBLEM: The seismic retrofit provided safety enhancements to the historic building;  however,  the roof and parapet walls no longer performed their watertight function. Due to the weather-induced expansion and contraction of the steel parapet brace, the waterproofing seal of the roofing membrane was compromised, allowing interior water infiltration. This situation required constant roof maintenance of the numerous and angled parapet brace penetrations. Additionally, the brick parapet walls were a continual cause of interior leakage, as wind-driven rain would enter the building through the mortar joints.

SOLUTION:  Wedge Roofing installed an insulated spray foam roof system custom-built of rigid closed-cell sprayed-in-place polyurethane foam. The liquid application adhered to and entirely coated the roof deck, filling every crevice, corner, gap, and angle change to form a waterproof seal around the seismic retrofit roof penetrations and parapet wall. The spray foam quickly expanded to form a solid, seamless monolithic roofing membrane, sealing the building envelope as both a thermal and moisture barrier. This spray foam roof was designed to withstand the building’s normal movement, including expansion, and contraction, without compromising the system’s integrity, as well as assisting in shearing and racking strength.

RESULT: This low-maintenance, long-lasting, cost-effective roof to alleviate the many challenges of the seismic retrofit of this historic commercial building. Installed directly over the existing roof membrane, the spray foam roofing offers a cost-effective and environmentally friendly alternative to complete roof removal and replacement. Covered with a UV-protective, reflective silicone coating, the new roof provides superior insulation, waterproofing, and reflective capabilities in compliance with California Title 24 Energy Goals to improve energy efficiency.