The MEP Coordination Drawing

The assumption that costs weeks

The usual belief is that if the air-conditioning designer, the electrical designer and the fire-protection designer have each produced a correct drawing, the floor can be built. It cannot, or not reliably. Each of those drawings is drawn against the architect's plan, and none of them knows what the others have done.

The result is that two trades have quite reasonably been given the same piece of ceiling void. Nobody is wrong on paper. The conflict only appears when the second trade arrives with materials and finds the first is already in the way.

The MEP coordination drawing is the document that resolves this before anyone arrives. For a decision-maker, the useful framing is this: it is one of the cheapest documents in a fit-out, and it protects the most expensive part of the programme, which is the middle third when several trades are working overhead.

What is on an MEP coordination drawing

A coordination drawing is not a bigger drawing. It is a layered one, where every service is drawn to its real size and its real height, and the space each one occupies is agreed.

Two things separate a real coordination drawing from a stack of drawings.

First, heights are shown, not just plan positions. Two services can share a plan location perfectly well if one is above the other. Without levels marked, a plan cannot say whether they fit. That is why sections matter as much as plans.

Second, clearances are drawn in. A duct needs its insulation, a valve needs room to operate, a damper needs an access panel and a light fitting needs clearance above it. A drawing that shows the bare service size passes routes that cannot actually be installed or maintained.

Checked at the tightest point

The most common way to get coordination wrong is to check a typical bay.

A typical bay tells you very little. Most of the floor usually has room to spare. The design succeeds or fails at the few places where everything converges: where a beam drops, where the main duct trunk meets a sprinkler main, where cable tray crosses a corridor, or where a service passes a structural element.

So the drawing needs sections cut through the worst locations, not a representative one. If the services fit there, the rest of the floor is unlikely to be a problem. If they do not, that is precisely what you needed to know before ordering.

This is also where the available ceiling depth becomes a real number rather than an assumption. The relationship between finished ceiling height, void depth and what must fit inside it is covered under plenum depth, and it is often the first thing a coordination drawing reveals is tighter than the design intent.

A related location is the slab edge and other penetrations, where services pass through fire-rated construction. Those points need the sealing arrangement resolved as part of the drawing rather than left to be improvised, which is what slab edge firestop describes.

Who produces it, and why ownership matters

The drawing is normally produced by the contractor or a specialist coordinator, working from each trade's design, and reviewed by the trade designers and the project's consultants.

What matters is not who holds the pen. It is that one named party owns the combination, has authority to require a trade to move, and signs the drawing off only when every trade has accepted it.

This is one place where the contract structure shows up. Where a single contractor is responsible for all the services, one party can resolve conflicts between trades. Where each trade is contracted separately, the conflict crosses a commercial boundary, and someone has to decide who moves and who pays. That difference is discussed in turnkey vs item-rate fit-out contracts.

Design coordination and site coordination are different jobs

They are often confused, and they cost very different amounts.

Site coordination is never fully avoidable. Structure is not built exactly to drawing, existing services turn up where they were not shown, and installers work to tolerances. But it should be dealing with small variances, not whole clashes. When site coordination is doing the work of design coordination, the programme is already in trouble.

What a clash costs once the ceiling is up

A clash found on a drawing costs an edit. A clash found in the void costs more in several ways at once.

• Demolition. Something already fixed must be removed. A duct or sprinkler main that has been installed and tested is not moved casually.
• Re-testing. Pipework that is altered may need to be tested again, and the sequence of tests then delays the ceiling closing.
• Waiting trades. Everyone behind the affected trade stops. This is the part that turns a local problem into a programme problem.
• Replacement material. A duct fabricated to a length and route may need to be remade, not adjusted.
• Knock-on to other trades. Moving one service often pushes a neighbour, which was itself coordinated.

None of these is dramatic on its own. The cost is that they are discovered when several trades are mobilised, and it is the idle time of that whole group that hurts. The specific cost depends entirely on the project, which is why it is better described as a sequence of consequences than as a number.

The ceiling void sequence the drawing must respect

The coordination drawing is only useful if it matches the order of work. Typically the void is filled in a sequence: structure and any strengthening first, then main ductwork, then sprinkler and other pipework, then cable containment, then lighting and devices, and finally the ceiling.

The drawing should reflect this. A service that must be installed early is given the space it needs first, and services that follow are routed around it. Drawn the other way, the last trade in finds the void already full.

Building services provisions are set out in NBC 2016, Part 8, and the fire-protection layout is governed by the fire and life safety provisions in NBC 2016, Part 4. Electrical installation practice is covered by IS 732. Which provisions apply to your building and how they affect routing must be confirmed by the project's engineers.

Common mistakes

Treating the coordination drawing as a deliverable, not a decision. It is produced, filed and never reviewed by the trades. The trades then build to their own drawings.

Coordinating only in plan. Without levels and sections, two services drawn in the same place are flagged as a clash when they are not, and real clashes at different levels are missed.

Leaving out the ceiling. The grid, tile module and light positions are what tell you where devices must sit. A coordination drawing without the ceiling leaves the visible result to chance.

Freezing it too late. If ductwork has been fabricated before the drawing is agreed, the drawing can only record the problem.

Ignoring access. Valves, dampers and junction boxes that have been coordinated into the void but are behind a fixed ceiling cannot be maintained. Access panels belong on the drawing.

Not marking the as-installed position. The void should be photographed and compared with the drawing before the ceiling closes. It is the last cheap chance to find a difference.

What to ask

• Who owns the coordination, and do they have authority to instruct a trade to move?
• Are there sections through the tightest locations, with levels shown?
• Does the drawing include the ceiling grid, light positions and access panels?
• Has each trade accepted it in writing, not simply received it?
• When does it have to be signed off, relative to ordering the long-lead items?
• How will the installed position be checked before the ceiling is closed?

A contractor who answers all six has a process. One who says the trades will sort it out on site has a risk.

Standards referenced

Building services provisions in NBC 2016, Part 8; fire and life safety provisions in NBC 2016, Part 4; electrical wiring installations in IS 732. The routing, clearances, separation and fire-related provisions that apply to a specific building must be confirmed by the project's engineers and consultants and, where relevant, the authority having jurisdiction.