How Are Tulsa's Historic Art-Deco Buildings Retrofitted?

No retrofit design begins without understanding the existing building. The assessment documents the structural system — steel frame with riveted or early bolted connections, concrete flat-slab or beam-and-girder floors, masonry bearing walls — and probes its condition: concrete sounding and coring where deterioration is suspected, steel coupon testing where strengths are unknown, and facade surveys that map every cracked terra-cotta unit, spalled limestone panel, and failed mortar joint. Original drawings are gold when they exist; when they do not, selective demolition and field measurement build the structural model the engineer analyzes. The seismic and wind evaluation typically governs the structural scope. Pre-war frames often lack the ductile detailing, diaphragm continuity, and wall anchorage the current code expects, and Oklahoma's induced-seismicity history gives the evaluation real teeth. An ASCE 41 evaluation grades the building's expected performance and produces the deficiency list the retrofit budget follows: unanchored parapets and veneer, flexible diaphragms, weak column-strong beam proportions, or discontinuous load paths. The assessment also flags hazardous materials — asbestos, lead paint, PCBs — because abatement sequencing affects the structural work schedule. This phase is groundwork, and on historic buildings it is the phase that prevents the expensive surprises.

Where a property carries historic preservation overlay zoning, the Tulsa Preservation Commission's Unified Design Guidelines control exterior work. The core rules are straightforward: retain and preserve historic architectural elements; match size, shape, pattern, texture, and orientation when replacement is necessary; keep work consistent with the building's style and period details; and base restoration on physical or pictorial evidence, not conjecture. Roof work must preserve the historic roof form and character-defining features; changing roof covering materials is reviewed case by case. Even porch and railing work on historic residential structures must navigate both the guidelines and the building code's safety requirements. For the project team, this means the structural and architectural designs are developed with preservation review in mind from day one. Facade anchors are detailed to avoid ornamental units; new rooftop equipment is screened and set back from the parapet; window replacements match the historic pattern rather than defaulting to modern storefront; and any new addition is designed to be compatible without mimicking. The guidelines are not anti-change — they are anti-thoughtless-change — and projects that engage preservation staff early, like the award-winning Petroleum Building loft conversion, move through review far faster than projects that treat the guidelines as a plan-check surprise. The AHJ's preservation and building reviews run in parallel, and both must be satisfied before permits issue.