The mechanical floor on a mid-century office conversion almost always disappears in the pro forma until someone opens the ceiling.

What is the existing electrical service size in amps, because that single number tells you whether you are upgrading a panel or rebuilding the entire riser system from the transformer?

The timing question is the one that actually matters here. A mechanical engineer in the building before the LOI is ideal, but most sellers will not grant access for a full assessment at that stage, so the practical answer is a phased ask: get a two-hour walkthrough with a licensed ME during the inspection period, before any earnest money goes hard, with the explicit deliverable being a systems conflict memo, not a full set of drawings.

What to ask for in that memo, specifically: where the existing stack locations land relative to your unit layout, whether the electrical service amperage and riser capacity can support residential load density without a full gear replacement, and whether the supply air chase geometry forces you into a corridor width that compresses your net rentable below what your rent comparables assume. That last one is the silent deal-breaker in mid-century steel-frame buildings because the corridor is already eating your efficiency ratio before MEP touches it.

The number doing the most work in the example you posted is not the $410,000 MEP line, it is the implied net rentable per unit. Thirty-eight one-bedrooms in 42,000 gross square feet is 1,105 gross square feet per unit, and after corridor, mechanical room, egress, and lobby the net rentable per unit in a building that resists the layout is probably closer to 680 to 720 feet, which changes the rent per foot your comps need to support before you can defend the capital stack. Did the original pro forma model net rentable explicitly, or was it backing into a per-unit average from the gross?

What's the plumbing stack count relative to your unit count, and where do the stacks actually land on the floor plate? That's the first thing I ask because in my experience the stack locations either make the bathroom layouts work or they make your per-unit cost jump $8,000 to $12,000 before you've touched anything else.

I get the ME in before I go hard, full stop. I paid $1,500 for a half-day walk on a Canton warehouse conversion that I ended up not doing, and that $1,500 saved me from a $200,000 mistake in the drain slope situation alone, same problem as the building in this post, horizontal runs that couldn't make code without dropping the slab.

The specific ask: I want a written opinion on whether the existing risers and stacks can be reused at all, not just modified, because "modify" is doing a lot of budget work in most pro formas I've seen and it almost always means replace.

The most common misconception worth correcting first: a preliminary MEP walk is not the same as a full scope-of-work document, and people treat the walk as if it resolves the budget when it only resolves the question of whether a full scope is worth commissioning. Those are two different deliverables with two different price tags and two different decision points.

What I would ask a mechanical engineer to price before going hard is not a full set of construction documents but a condition assessment with a rough order of magnitude tied to three specific questions: where does new vertical chase space come from given the existing structure, what is the realistic panel and riser replacement cost given the service entry location and available easement, and what is the longest allowable horizontal drain run given the slab elevation and whether the slab can be cut without hitting post-tension cables. That last one resolves the bathroom layout question before any appraiser ever sees a floor plan. The fee for that assessment on a building this size typically runs somewhere between four and eight thousand dollars, which is cheap against a $700,000 MEP swing.

The timing that works is commissioning that assessment concurrent with the title and survey review, so all three land before the hard money deadline rather than after it. The building in your example told the whole story in the chase locations and the panel room, and a two-hour walk with the right questions written down in advance would have surfaced the corridor conflict before the LOI.

What did the floor-by-floor slab construction look like, and was there any post-tension present that ruled out cutting new drain penetrations?

The $690,000 gap between that MEP line and reality is almost exactly what I watched kill a 1964 brick office in Kanab two years ago, except ours was a $480,000 swing and the sponsor ate it personally because the contingency was already spent on asbestos abatement nobody priced either.

What does your corridor layout actually require in terms of chase relocation, and did the engineer walk it with the architect in the room at the same time, or separately?

That last part matters more than people admit. When they walk it separately you get two documents that don't talk to each other and the conflict lives in the budget as a gap until demolition day.

The assumption doing the most work in your post is that a mechanical engineer walking the building produces a number you can use. What it actually produces is a scope, and scope without a quantity takeoff is still a guess with better credentials. The figure that changes behavior is not "full panel replacement and new risers" but the linear footage of new riser, the number of panel positions, and whether the utility will serve a new transformer or you are paying for that too, because those three items alone can spread a $400,000 estimate across a range wider than your acquisition price.

The specific ask I would give the engineer before going hard is this: price the worst bathroom location in the building, not the average one. If the stack placement forces a horizontal drain run that approaches the slope limit, that unit tells you more about the project's true floor than any aggregate MEP number does, because it is the constraint that either kills your layout or forces a structural penetration that then touches your structural engineer's scope.

What is the ownership structure of the entity that controlled this building through that LOI period, and did anyone in that entity have conversion experience, or was this the first adaptive reuse in their portfolio?

The risk nobody in this thread has priced is the mechanical engineer's preliminary scope becoming the GC's change order vehicle. When the ME walks pre-LOI and produces a narrative report rather than a priced scope, the GC bids against the narrative, not against a set of drawings, and the gap between those two documents is where the overrun lives. On a 42,000-square-foot shell, asking the ME to produce a rough quantity takeoff alongside the walk, not just a condition assessment, gives the GC something to price against and surfaces the delta before you go hard.

The specific question I would add to whatever list you bring into that walk: ask the ME to identify any existing penetrations, chases, or structural bays that could accept new plumbing stacks without horizontal relocation, and price the cost difference between a unit layout that uses those locations versus one that ignores them. That is a unit-plan constraint masquerading as an MEP constraint, and catching it pre-LOI lets you redesign the floor plate before the architect has billed forty hours on a layout the plumbing will reject anyway.

At what acquisition price per foot did the seller's broker justify the $31, and was there a prior feasibility study you can request in due diligence to see what MEP assumptions the last buyer was working from?