How do floor-plate, plumbing, and elevator feasibility affect conversion financing?

Feasibility metrics that drive lender appetite and the advance-rate haircut

Floor-plate depth: residential apartments need exterior windows. Floor plates with depth greater than 35 to 40 feet from window to core require interior light wells, atria, or unit configurations that don't penetrate to the core. Per architect feasibility studies, sub-40-foot depths are strong-conversion candidates; 40 to 60 feet are moderate; over 60 feet usually drives the deal to demolish-and-rebuild instead of conversion.

Plumbing-stack count: office buildings have one or two plumbing stacks per floor; residential conversion typically needs 6 to 10+ stacks per floor for unit kitchens and bathrooms. Re-routing existing stacks plus running new stacks is a major hard-cost line, typically $30 to $80 per residential SF on a moderate conversion. The number of new stacks required gates the construction cost.

Elevator and life-safety: residential apartment count drives elevator-cab requirement (typically one elevator per 100 to 125 units in NYC code; varies by jurisdiction). Office buildings often have higher elevator capacity per tenant FT than residential needs, which is favorable. Life-safety: residential sprinkler density, exit pathway counts, and code compliance for residential occupancy must be designed.

Window operability and HVAC: residential code typically requires operable windows in habitable rooms. Office curtain walls with non-operable glass require replacement or major retrofit. HVAC zoning: office-grade central VAV systems can't deliver per-unit residential climate control without major reworking. PTACs, VRF systems, or per-unit air-source heat pumps are common solutions but add capex.

Lender response: lenders require a third-party feasibility study at pre-development that assesses each of these dimensions. A strong-feasibility profile (sub-40-foot depth, manageable plumbing, modest elevator and life-safety adds) gets the deepest construction lender options at the lowest pricing. A marginal profile pushes pricing wider, advance rate lower, and may require additional sponsor recourse or contingency reserves.