FORENSIC DUE DILIGENCE
FORENSIC DUE DILIGENCE • PHASE 2: DESIGN & DOCUMENTATION • ARTICLE 12
Why some of the most expensive building defects are born not in the field, but in the gaps
between four sets of drawings. By Nate MacIntyre — Construction Science Forensics, LLC
When I am retained to investigate a building that is leaking, sweating, tripping breakers, or failing inspection after occupancy, I rarely find a single villain. More often I find four well-designed systems that were never designed to live together. The mechanical engineer sized the ductwork. The electrical engineer sized the feeders. The plumbing engineer pitched the drains. The fire protection contractor laid out the sprinklers to NFPA 13. Each was correct in isolation — and all of them wanted the same eight inches above the ceiling. That is the quiet truth about MEP coordination: it is rarely the glamorous part of a project, and it is one of the more reliable predictors of whether a building will perform. This article is about how to read MEP design and documentation during the due diligence window — before drawings become concrete, conduit, and claims.
What “MEP Coordination” Actually Means
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MEP stands for mechanical, electrical, and plumbing — and in practice the fourth discipline, fire
protection, travels with them. MEP coordination is the process of reconciling these systems with one another, and with the building’s structure and architecture, so that every component has a real, buildable, code-compliant place to exist. Coordination is not the same as design. A discipline can be fully designed and still be completely uncoordinated. Coordination is the deliberate act of overlaying those designs — ideally in a single composite model or coordination drawing set — and resolving the conflicts that emerge: a duct that runs through a beam, a sprinkler main that blocks an access panel, a panelboard with no coderequired working clearance, a drain line that loses its slope. In my forensic work, I treat the coordination process itself as evidence. When I find no coordination drawings, no clash-detection log, and no record of who resolved what, I am usually looking at a building whose conflicts were resolved by the trades, in the field, under schedule pressure — and that is where latent defects are born.
Four Disciplines, One Building
Each MEP discipline answers to its own body of standards, and each carries its own forensic signature when it goes wrong.
The four MEP disciplines, the authorities that govern each, and the issues they most often surface in coordination.
▪ Mechanical (HVAC) is governed by the International Mechanical Code (IMC), with ventilation rates from ASHRAE Standard 62.1, energy requirements from ASHRAE 90.1, and — on Construction Science Forensics, LLC
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residential work — load calculations and equipment selection following ACCA Manuals J, D, and S. The classic mechanical coordination failure I have investigated is condensate: a cooling coil or refrigerant line that produces water with nowhere for it to drain, which then finds its way into the building envelope. ▪ Electrical is governed by the National Electrical Code (NFPA 70). Beyond conductor and overcurrent sizing, the coordination issue I see most often is working space — the clear area the NEC requires in front of panels and equipment (NEC 110.26) that other trades quietly consume with pipe, duct, or storage. ▪ Plumbing is governed by the International Plumbing Code (IPC) and the design practices codified by ASPE. Plumbing is unforgiving in one specific way: drainage runs on gravity. A drain or storm line must hold its slope, so when it conflicts with a duct or beam, the pipe is usually the thing that cannot move. ▪ Fire protection spans several NFPA standards — NFPA 13 for sprinklers, NFPA 14 for standpipes, NFPA 20 for fire pumps, and NFPA 72 for fire alarm and signaling — and intersects the International Fire Code (IFC) and the penetration and damper provisions of the International Building Code (IBC §714 and §717). It is the discipline most likely to be installed last, and the one whose coordination failures carry the highest life-safety stakes. Local note for Pacific Northwest work: in Oregon these map to the Oregon Mechanical, Plumbing, and Structural Specialty Codes and the Oregon Energy Efficiency Specialty Code; Washington adopts parallel state amendments. The principles are identical; the adopted editions and section numbers differ.
Why Coordination Is Hard: The Congested Plenum
If you want to understand MEP coordination in one picture, look up at a ceiling that has been removed. The space between the structure above and the finished ceiling below — the plenum — is some of the most contested real estate in a building. Into that narrow band we ask the design team to fit supply and return ductwork, domestic water, sanitary and storm drainage (which must stay sloped), electrical conduit and cable tray, sprinkler mains and branch lines, lighting, and structural members that refuse to move.
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A single plenum band, drawn to show what coordination has to solve before the drawings reach the field.
The geometry is genuinely difficult, and sequence makes it harder. These systems are typically
designed by different firms, on different drawing sheets, at different times. The mechanical drawings show the ducts; the plumbing drawings show the pipes; neither necessarily shows the other. Unless someone overlays them deliberately, the first place all four systems “meet” is the jobsite — the most expensive possible place to discover that they do not fit. This is why the standard of care on well-run projects leans on composite coordination drawings and, increasingly, BIM-based clash detection: building the conflict in a model so it can be resolved with a mouse instead of a reciprocating saw.
How an MEP Coordination Gap Becomes a Claim
Most of the MEP failures I investigate followed the same path, and it almost always starts at the drawing set, not the jobsite.
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The pathway I trace backward in nearly every MEP investigation — from the loss to the documentation that allowed it.
It begins with a design gap: systems documented separately with no composite review. It proceeds
to a field workaround, where a foreman — doing exactly what the schedule demands — reroutes a main, notches a structural member, or drops a ceiling to make the pieces fit. That workaround becomes a latent defect: a condensate line that no longer drains, an access panel buried behind a duct, a fire-rated assembly compromised by an unsealed penetration, a code clearance quietly erased. Finally, often months or years after occupancy, the defect surfaces as a claim — water intrusion, equipment failure, a failed re-inspection — and someone calls a forensic consultant to trace it backward. The important point for due diligence is that every one of those downstream costs was decided upstream, in documentation. The cheapest defect to fix is the one still living on a drawing.
A Composite Case (Illustrative)
The following is a composite drawn from patterns I see across multiple investigations, not a single real project; details are generalized to illustrate the mechanism. A mid-rise residential building begins reporting moisture staining on top-floor ceilings within its first cooling season. The first assumption is a roof leak. The investigation finds the roof intact — the water is condensate. During design, the mechanical and structural drawings were never overlaid; in the field, the installing contractor rerouted a run of cooling-supply ductwork to clear a beam that the duct, as drawn, would have run straight through. The reroute introduced a low spot, and the secondary condensate drain that should have caught an overflow had been omitted where the layout changed. Warm, humid air condensed on the cold duct, pooled at the low point, and migrated into the ceiling assembly. No single party set out to build a defect. The defect was the sum of an uncoordinated drawing set and a reasonable field decision made without the full picture. A composite coordination review Construction Science Forensics, LLC
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during design would have caught the duct-beam conflict on a screen — and the secondary drain would never have been “lost” in a field reroute.
What I Review During the Design-Phase Due Diligence Window
When I am asked to review MEP documentation before or during construction — rather than after a loss — I look for a short list of high-leverage indicators. None of these requires you to be an engineer; they are questions an owner, developer, or owner’s representative can reasonably ask. What to look for
Why it matters
Anchored to
Composite coordination
drawings or a federated BIM model
Confirms the systems were overlaid and
conflicts resolved on paper, not improvised in the field
Project specifications; standard of care
Clash-detection report and
coordination sign-off log
Provides the audit trail — who resolved each
conflict, and when
BIM execution plan
HVAC load calcs and equipment
schedules
Verifies sizing, ventilation, and that
condensate was designed rather than assumed
IMC; ASHRAE 62.1 /
90.1; ACCA J/D/S
Primary and secondary
condensate management
A leading cause of post-occupancy “phantom
roof leaks”
IMC condensate
disposal provisions
Electrical working clearances at
panels and equipment
Clearances are routinely consumed by other
trades after layout
NFPA 70 (NEC) 110.26
Drainage slope continuity and
venting
Gravity systems cannot be rerouted freely; lost slope means standing water
IPC; ASPE practice
Fire-rated penetration and
damper schedule
Every MEP penetration of a rated assembly
must be addressed
IBC §714 / §717; IFC; NFPA 13 / 72
Access for maintenance (valves, dampers, cleanouts, panels)
Buried access drives change orders and
deferred maintenance
IMC / IPC access
provisions
Coordination where MEP
penetrates the building envelope
A frequent and costly water-intrusion path
Project details; envelope
review
The Bottom Line
MEP coordination is unglamorous, invisible when it works, and disproportionately responsible for the defects that end up in front of people like me. The encouraging part for owners, developers, and owner’s representatives is that it is also one of the most reviewable parts of a project during the due diligence window.
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You do not need to be an engineer to ask the questions that matter: Were the systems overlaid? Who
resolved the conflicts, and is it documented? Do the access, clearance, slope, and penetration details survive contact with reality? A building tells you, in its documentation, whether its systems were ever introduced to one another. Reading that story early is some of the highest-return diligence available — and far cheaper than reading it later, in a report with my name on it.
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