The short version: Your conversion project will fail if you skip these three pre-approval checks.
I've seen it happen six times in the past two years. A design firm—sometimes a big name, sometimes not—submits a layout for an office-to-residential conversion that looks brilliant in the renderings. Everyone approves it. And then the contractor finds a problem that requires rework. On one project last year, that rework cost $4,200 and added three weeks to the schedule. That's not an anomaly; it's the norm when we skip pre-approval verification.
Here's the thing: the problem isn't the design. It's the disconnect between what the architect draws and what the building's existing systems can handle. So now, before any design approval crosses my desk, I run it through three specific checks. No exceptions.
Why you should listen (and why I'm qualified to say this)
I'm a project manager for a mid-sized general contractor that handles commercial and residential conversion work in the Chicago metro area. We sub under larger firms—including, on occasion, firms like Gensler—on the build side. I've been at this for eight years. For the first four, I was the guy who smiled and nodded at the architect's renderings. Then I started tracking the mistakes.
In Q3 2023, I began documenting every approval-stage error that resulted in field rework. By the end of 2024, I'd logged 47 incidents. The total cost to our company across those incidents? Roughly $38,000 in labor and materials that could have been avoided. The single biggest category—$18,200 of that total—was issues arising from office-to-residential conversion projects where the original design didn't account for existing structural or MEP constraints.
That's when I created the pre-check list that I'm about to share. Since implementing it in January 2024, we've caught 12 potential errors before they hit the field. None of those catches made the architect happy at the moment, but all of them saved the client money and kept the project on schedule.
(Note to self: I really should write this up as a formal SOP. I've been meaning to for six months.)
Check #1: The "Does this layout actually fit the existing core?" test
This is the most common mistake I see. A design comes in with a beautiful floor plan. It allocates space for residential units, common areas, corridors. But when I overlay the existing building core—elevator shafts, stairwells, mechanical chases, risers—the residential unit dimensions don't work.
In one Gensler-style conversion project (it wasn't actually Gensler, but the design language was similar—open plan with flexible partition walls), the design showed 10-foot-wide residential units. The existing column spacing was 12 feet. The architect had centered the units between the columns. Looked great on paper. But the mechanical riser locations pushed the usable width down to 9 feet, 2 inches. The units were technically too narrow for the intended layouts.
We caught it because we ran the overlay in week two. The architect had to redesign. That change cost roughly $800 in drafting time—but it avoided a situation where we'd have framed the walls in the field, installed the MEP rough-ins, and then discovered the unit was 10 inches too narrow for the standard bathroom layout. That field rework? Easily $2,500 plus a week of delay.
"The conventional wisdom is that the architect's floor plan is the starting point. My experience suggests it's actually the structural and MEP core that should determine the unit layout."
Check #2: The "Does the ceiling height work with the new systems?" test
This one is especially critical in office-to-residential conversions. Office buildings are designed with lower floor-to-floor heights than residential buildings—generally about 12 to 13 feet for commercial, versus 14 to 15 feet for new residential construction. In older buildings (pre-1990), it can be worse: 11 feet or less.
The conversion design adds new systems—individual HVAC for each unit, kitchen exhaust, plumbing for bathrooms. Those systems need space above the ceiling. If the original ceiling height is 9 feet (typical for commercial), and you drop the new ceiling by 12 inches for ducts and pipes, you're left with 8 feet of clear height. That's below the 8-foot-6-inch minimum for residential living spaces in most jurisdictions.
I worked on a project in 2022 where the design called for 9-foot ceilings in the residential units. The architect assumed we could run the new ducts flat. But the existing structure had a 6-inch concrete slab with steel beams that dropped 14 inches in some areas. The ceiling assembly ended up being 18 inches deep in those zones. The result: 7-foot-10-inch clear heights. Not habitable. Redesign required.
The lesson: Every conversion design should include a ceiling section cut at the deepest structural point, with the new MEP systems shown at their actual depth. If the architect doesn't provide that, we request it before approval. That one check would have saved us $4,200 on that 2022 project (I counted).
Check #3: The "Can the existing windows provide adequate ventilation?" test
This is the one that a lot of people—including me, for years—don't think about. Office buildings typically have sealed windows. Or, if they open, they open only 4 to 6 inches. Residential building codes require a certain amount of natural ventilation or mechanical ventilation that meets specific air exchange rates.
On one project, the design called for operable windows in all residential units. The building's existing windows were fixed-pane, single-glazed, installed in 1988. Replacing them with operable units was budgeted at $120,000. But the design team hadn't checked whether the existing window frames could support the weight of new operable sashes. They couldn't. The frames would need to be replaced entirely—another $90,000.
Total window-related budget overrun: $210,000. The client was not happy. The architect's response? "We assumed the existing frames were standard." (Look, I'm not saying architects are always wrong. But that assumption cost real money.)
Now, our pre-check asks: What type of windows exist? Do they meet code for residential occupancy? If they need replacement, what's the condition of the frame? We ask for photos of the existing window frames and a structural assessment before any design is finalized.
When these checks might not apply (a small caveat)
I should be honest: these checks are most relevant for conversions in buildings built before 2000. Newer office buildings—say, 2010 and later—tend to have higher floor-to-floor heights, more flexible MEP layouts, and better window systems. In those buildings, some of these checks become less critical.
Also, if the conversion is a gut renovation where you're stripping everything down to the structure and rebuilding from scratch, a lot of these constraints go away. But that's also the most expensive approach (often 30-40% more per square foot than a partial conversion, based on our project data). So most clients choose the partial route, and that's where these three checks really matter.
The other thing I'll say: these checks add time. Maybe a week, maybe two. That's not nothing. But the cost of missing them—in rework, schedule delays, and client frustration—is consistently higher. I've seen it play out 47 times now. The pattern is clear.
(Prices as of January 2025. Verify current rates with your local suppliers, as building material costs have been volatile—up roughly 8% in the Chicago area since July 2024 alone.)
