Design Coordination vs. Field Coordination: Where MEP Clashes Get Solved

There's a photo in our files of a rectangular supply duct with a special fitting fabricated into a straight section of ductwork so a bundle of conduit and PEX could pass through. Someone made that decision in the field — which likely meant an extra trip from the shop to the site, and custom fittings are not free. It worked. It also wasn't in anyone's design, nobody checked what the fitting did to the duct's effective area or its pressure drop, and the owner paid for that run twice: once to fabricate it, once to install it. That's field coordination doing work design coordination should have done. Every project needs both. Only one of them is cheap.

This post covers what separates design coordination from field coordination, what real design coordination looks like inside a 3D Revit model, and why the lowest design fee on the table is frequently the most expensive number in the project.

Key takeaways

• Design coordination resolves system conflicts in the model before bid; field coordination resolves them in the ceiling after material is bought and hung.

• Field coordination is unavoidable and valuable — but every clash it absorbs arrives as an RFI, a change order, or rework, all priced at construction rates instead of design rates.

• Real design coordination requires modeling MEP systems to something like BIMForum LOD 350, where the interfaces between systems are actually drawn, not represented by single-line placeholders.

• Coordinated models have to budget the ceiling cavity for more than pipe and duct: NEC 2023 Section 110.26 working space, IMC 2021 Section 306 equipment access, NFPA 13 sprinkler obstruction rules, valve access, and filter pull space.

• Good modeling takes hours, and those hours show up in the fee — which is why AEG is not always the lowest design number on a bid tab.

• In our experience, a single avoided ceiling-height change order or one week of recovered schedule typically exceeds the entire delta between the low fee and the coordinated fee.

Design coordination and field coordination are two different jobs

Design coordination happens before bid, in the model, and the engineer owns it. The structural, mechanical, electrical, plumbing, and fire protection models get federated and run against each other. Conflicts get resolved on screen, where moving a main costs a few minutes of a designer's time. The output is a set of documents where the systems fit in the space provided.

Field coordination happens during construction, in the building, and the trades own it. Contractors sequence their installations, confirm actual conditions, hang first, and work around what's already there. This is legitimate work — dimensions drift, structure gets shimmed, equipment substitutions change connection points, and no model matches a finished building exactly.

The two are not interchangeable. Field coordination is designed to absorb the last few inches of variance. It is not designed to absorb a main trunk that was never routed around a beam. When it has to, the trade with the most schedule pressure wins, the resolution never gets documented, and the owner inherits a building that doesn't match the record set.

Here's the part we hear most from new clients: they assumed design coordination was already happening on their projects. On paper it was. In the documents, it wasn't. Single-line diagrams, generic ceiling plans, and a note directing the contractor to "coordinate in field" is not coordination. It's a transfer of the problem, downstream, to the most expensive place to solve it.

What design coordination looks like when it's actually done

We model in Revit, and we model to be coordinated — not to produce a plan view that prints well. Practically, that means:

• Systems drawn as they'll be built. Duct with actual dimensions and insulation thickness, pipe with fittings and hanger space, conduit racks with real bend radii. BIMForum's Level of Development Specification calls this territory LOD 350 — the level where connections and interfaces with other systems are modeled rather than implied.

• A federated model, checked on a schedule. Structural, architectural, and each MEP discipline in one coordinated environment, with clash detection run at design development and again through construction documents. Clashes get resolved and logged, not just flagged.

• A ceiling cavity budget. Elevation targets by corridor and room, established early with the architect, so plenum depth is a design constraint everyone is working to instead of a discovery made in the field.

• Access and clearance modeled as real geometry. NEC required working space in front of panels. Equipment access and working space per IMC. Sprinkler obstruction rules under NFPA. Filter pull, coil pull, valve handles, and cleanout access. These are the boring details that get missed, and they are what turn a "coordinated" project into an uninstallable one.

• Structural penetrations coordinated with the structural engineer. Sleeve and opening locations reviewed against the framing before the drawings go out, not sorted out by phone once the trades are on site.

That work takes time, and the time is real. It's the reason our fee is sometimes higher than the number next to it on a bid tab. We'd rather explain the fee up front than explain the change order later.

Why the lowest design fee is rarely the lowest project cost

Mechanical, electrical, and plumbing design typically runs a modest percentage of MEP construction cost. The change orders that come out of uncoordinated documents don't scale that way. When a main won't fit above a corridor ceiling, the options are all expensive: drop the ceiling and lose the finish detail the architect drew, reroute in the field at premium labor, revise the design mid-construction, or push the schedule. On projects with a leaseback date or a school calendar, the schedule cost dwarfs the material cost.

The pattern we see is consistent. Uncoordinated documents produce RFI volume, and RFI volume produces two things nobody budgets: contractor overhead priced into the change order, and design team hours spent answering questions that a model would have answered for free. The fee delta between a low-cost design and a coordinated one is usually a relatively small number. The change orders it produces are not.

We're not claiming a coordinated model eliminates change orders. It doesn't. Existing conditions surprise everyone, floor plans change, and equipment lead times force substitutions. What a coordinated model does is remove the category of change order that comes from systems that never fit in the first place.

Design coordination vs. field coordination: FAQs

What is the difference between design coordination and field coordination?

Design coordination is the resolution of system conflicts in the design model before construction, and it's the design team's responsibility. Field coordination is the resolution of conflicts during installation, and it's the contractors' responsibility. Design coordination is preventive and costs design hours; field coordination is reactive and costs construction hours, RFIs, and schedule. Both happen on every project — the question is how much work is pushed from the first into the second.

Doesn't the contractor coordinate everything in the field anyway?

Contractors coordinate the last few inches, and they're good at it. What they can't do economically is absorb a routing problem after material is fabricated and hung. Trade sequencing means the first trade in the ceiling gets the space and everyone after works around it, which is efficient for that contractor and expensive for the project. Field coordination is meant to handle variance, not design gaps.

What does 3D Revit modeling add over 2D MEP drawings?

A 2D plan can show two systems occupying the same space and still look correct, because nothing in the drawing checks elevation. A modeled system carries real dimensions in three axes, so clash detection can be run against structure and the other disciplines and the conflict shows up before bid. It also makes the ceiling cavity a measurable quantity the whole team can design against, rather than an assumption.

Why is a coordinated design fee higher than a low-bid design fee?

Because modeling MEP systems to a coordinated level of development takes more designer and engineer hours than producing single-line documents, and the fee reflects those hours. That's the honest answer. The comparison worth making isn't fee to fee — it's fee plus change orders plus schedule impact, evaluated at the end of construction rather than at the bid tab.

When should design coordination start on a project?

Early enough that ceiling heights and shaft sizes are still decisions rather than constraints — typically at schematic design for major routing and vertical distribution, with clash detection beginning at design development. Coordination introduced during construction documents can still catch conflicts, but by then the architectural section is usually fixed, which removes the cheapest solutions from the table.

When to bring in an engineer

Architects should engage an engineer who models and coordinates in 3D when:

• Ceiling heights are tight, or the design depends on an exposed structure or a specific ceiling detail

• The project has significant vertical distribution — multi-story shafts, stacked mechanical rooms, or a constrained penthouse

• The building type carries heavy MEP density: healthcare, laboratory, commercial kitchen, luxury residential, or hospitality

• A renovation puts new systems into existing structure where field conditions are already tight

• The owner has a hard delivery date, and schedule risk is a bigger exposure than first cost

• Structural penetrations need coordination before framing or shop drawings are released

• Your last project generated a stack of MEP RFIs and you don't want a repeat

You will get coordination on your project either way. The choice is whether it happens in the model, on your schedule, at design rates — or in the ceiling, on the contractor's schedule, at construction rates.

Axiom Engineering Group works on projects coast to coast. Learn more about our structural, mechanical, plumbing, and commissioning services: aeg.design

About the author: John Melvin, PE, is the CEO of Axiom Engineering Group, an SMEP engineering and commissioning firm with offices in Missoula, MT, Salt Lake City, UT, St. George, UT, and San Diego, CA. John is a licensed Professional Engineer with over 20 years of experience designing mechanical, plumbing, and electrical systems for commercial, institutional, hospitality, healthcare, and luxury residential projects.