Application to replace sidewalk at 27–29 Great Jones Street cites deteriorated granite flags and corroded support beams

Representatives for the building at 27–29 (2729) Great Jones Street requested permission to replace the existing sidewalk slabs above vaults after documenting corrosion and water infiltration under the granite and concrete flags.

The presenter, speaking on behalf of structural engineer Steven Wong and the building, said the existing sidewalk includes heavy granite slabs (about 10 inches thick) supported directly on steel beams with no curb or waterproofing; joints have allowed water to pass into the vaults below, causing corrosion, delamination and damage to mechanical and electrical equipment. The presenter showed photos of vault spaces where electrical equipment had been recently replaced and of areas where ceiling elements had fallen away from pump rooms due to moisture and deterioration. He said the building has been paying frequent caulking costs but that the steel beams are now compromised and that reinstalling granite in the existing structural configuration would be cost prohibitive and would require removing more of the structure.

The engineer's proposal described replacing the sidewalk with a new two-slab concrete system: a structural slab with a waterproofing membrane and a pigmented concrete wearing surface intended to match adjacent sidewalks. The presenter said the pigmented concrete would be selected to blend with neighboring sections that already have poured concrete slabs and that the alternative of re-installing granite wear slabs on a new waterproof deck had been studied but judged financially and structurally impractical in the current condition.

Public commenters raised preservation concerns, noting granite sidewalks are part of neighborhood historic fabric and encouraging the commission to require reinstatement of a granite wear surface when possible. Committee members discussed options including installing a waterproofed structural slab and then applying a granite wearing surface atop it, if structurally feasible. One committee member said they were "attracted to the idea of putting a granite wear surface back onto the new sidewalk if possible." The committee agreed to recommend further study of reapplying a granite top layer on the new waterproofed deck and to return guidance to the applicant; no formal roll-call vote was recorded in the transcript.

Ending: The committee requested additional documentation and color samples for the proposed pigmented concrete and asked the applicant to investigate feasibility and cost of reinstalling granite as a wearing surface over a new waterproofed deck.