Stop Thinking of Office Conversions as Simple Retrofits
I’ll be blunt: I used to think office-to-residential conversions were a PR stunt. A nice story for a developer to tell, but structurally a nightmare. For the first three years of my career at Gensler handling construction coordination for large-scale office projects, I’d roll my eyes every time a client brought it up. Slapping a kitchenette into a floor plate built for cubicles? Good luck with the plumbing core.
That was my opinion in 2021. Since then, I’ve personally coordinated the documentation on two major conversion projects here (totaling roughly 340,000 square feet, one in Chicago, one in D.C.). I also spent a good chunk of 2024 building our team’s internal checklist for these conversions because we kept making the same expensive mistakes.
The conventional wisdom is that conversions are primarily about zoning and financing. That’s not wrong, but it ignores the harder truth. My experience suggests otherwise.
“Everything I’d read about residential conversions said the biggest challenge was the ‘bathtub in the window’ problem. In practice, the existential issue is something far more boring and far more expensive: the vertical plumbing riser.”
Here’s what I’ve actually learned about making these projects work—and where we’re still failing in 2025.
The First Major Pitfall: Assuming the Core is a Core
When I started my first conversion in early 2022, I just assumed the existing mechanical core would be semi-adaptable. After all, office towers have bathrooms. The issue isn’t horizontal plumbing (running a line to a new apartment). The issue is vertical capacity.
On that first project, we planned for 72 residential units. The existing plumbing core (designed for a 1990s office tower with roughly 800 occupants) could only handle waste and supply for about 45 units without a massive, noisy, expensive re-stack. We discovered this after we’d already submitted initial drawings. That oversight cost us a 3-week delay and roughly $120k in re-design fees (thankfully, the client had contingency, but it wasn’t fun explaining it on a call with the CFO).
This is the single biggest issue I see developers underestimate. You can’t just look at the available floor area. The core is a finite resource. We now mandate a full plumbing riser capacity survey before we even write the feasibility memo.
The Second Pitfall (Ugh, This One is Embarrassing): Window Grids
This sounds trivial, but it’s a budget killer. Office curtain walls are designed for an open plan. They have a mullion grid that assumes you’ll have desks in the middle of the space. Residential layouts require that each livable room has a certain percentage of glazing, and that the window sill is at a certain height.
In September 2022, I worked on a project where the existing window grid put the horizontal mullion at exactly 38 inches. The residential code for that jurisdiction required a maximum sill height of 36 inches for egress in a bedroom. That 2-inch gap meant we had to either replace 47 specific window panes (in a building that was fully occupied on lower floors) or adjust the entire floor plan to avoid putting bedrooms near the problem windows. We chose the floor plan adjustment; it worked, but it killed the efficiency of the layout. We lost 3 potential units.
The lesson? Don’t assume curtain wall is “good enough” until you’ve checked the mullion grid against the residential egress code for exactly that floor. “Office” and “Residential” building codes are not just different—they’re often contradictory.
The One Thing That Actually Made it Work
I wish I could say we solved all this with high-tech BIM modeling. And we did use Revit extensively. But the game changer was something more basic: we changed our team structure.
Gensler is unique because we have deep interior design capacity. For the D.C. project, we embedded a senior interior designer (someone who normally does luxury multifamily) into the core construction team from day one. This wasn’t a ‘hand-off’ where the architects design the shell and the interior team does the finishes. The interior designer sat in on the structural review meetings. She identified six specific column locations that would have interfered with her typical kitchen/dining layouts. We shifted those columns by 4-6 inches (within structural tolerance) during the design development phase. Total cost of that move: maybe $8k in re-draws. Cost if we’d caught it during construction? Probably north of $60k and a huge schedule headache.
This is hard to replicate if you’re a pure architecture firm that subcontracts interiors. The integration matters.
So, Is the Hype Overblown?
Look, I’m not going to tell you conversions are a silver bullet for the vacant office problem. They are hard. The economics are brutal if you don’t account for the plumbing and the window issues I mentioned. A lot of projects that get announced in the press quietly die during the feasibility study. I don’t have hard data on that failure rate (I wish I did), but from talking to peers, my sense is that maybe 40% of announced conversion projects actually break ground.
But I was wrong to dismiss them as a gimmick. For the right building—one with a reasonably flexible core, good floor plates (narrow enough for natural light), and a location that supports residential amenity density—the transformation is real.
The fundamentals haven’t changed: you still need a good location and a sound envelope. But the execution has transformed. It’s not about just ‘making it work.’ It’s about doing the boring pre-work on the vertical risers before you sell the vision to the investment committee.
Stop thinking of conversions as a retrofit. Start thinking of them as a surgical transplant that requires a very specific donor building. My checklist now starts with a riser and a mullion. Everything else is the fun part.
