Bring the MEP engineer in at schematic design, before ceiling plans are drawn and finishes are picked. That is the point where systems can still be routed to fit the architecture instead of fighting it. By the permit set, the decisions that set ceiling height, shaft space, and operating cost have already been made.

When should the MEP engineer join the design?

At some point in time in any project, one gets the impression that the design starts becoming disjointed. The ceiling plans are all done, the finishes have been picked, the client loves some portion of it, and the engineer is not involved in the design process as yet. Everything looks fine until then and there lies the problem.

The correct stage of inclusion is at the schematic stage, before which many architects usually involve the engineer, and before the stage at which the system becomes routable to the architectural needs instead of vice versa. By including the engineer at the schematic stage, engineering will be incorporated effortlessly in the building.

Including him only at the permit set stage is what compromises were not intended initially.

It is at this schematic phase that when there are uncertainties on the height of ceilings, shafts, and massing, the system selection and layout may still be modified without having to modify drawings. This is the only time in which MEP can be designed in a way to complement rather than contradict the design.

Every other subsequent phase will only reduce choices.

Why do MEP systems eat into ceiling height?

Since the plenum above the ceiling represents shared space, it will feature pipes, ducts, vents, and structural members, and since the depth of the deepest assembly of any particular run dictates the ceiling of that particular run, the two most common culprits in a South Florida building are the air-conditioning ducts and the plumbing dropping down from the floor above.

The air-conditioning ducts represent the deepest member in that space because the building belongs to ASHRAE climate zone 1A, which features more than 9,000 cooling degree-days (base 50°F) and a dehumidification before temperature control climate, hence a great amount of airflow needs to occur, requiring large ducts.

There are two additional aspects here that make the situation even worse in comparison to what one would expect when designing: each supply duct is insulated and therefore its effective depth is greater than the sheet metal depth; ducts are deep only near the air handler and get smaller as they branch off towards the rooms.

This represents an architectural lever rather than just a mechanical problem because the place of the air conditioning closet defines the place of deep ducts.

Two architectural solutions, both of which need to be chosen on the schematic level, are possible to avoid any conflicts between the ducts and headroom:

• Locate those rooms that require the highest headroom far from the air handler, where the trunk ducts become smaller
• Program the floorplate to allow large trunk lines of deep ducts through secondary spaces: closets, corridors, back-of-house areas, where low ceiling doesn’t impose any penalty and then branch off into the interesting rooms with shallower ducts allowing taller ceilings.

How does plumbing from the floor above lower the ceiling below?

With regards to multi-stories, drainage, condensate and exhaust from above come down through the ceiling of the floor below it.

Some part of it must be sloped.

The Sanitary Drain needs to be sloped to the fixed grade as defined in the plumbing code, which is 1/4 inch per foot for small branch lines (less than 2 inches), and 1/8 inch per foot for large mains (between 3 and 6 inches). In long horizontal lengths, it will lead to sagging of the ceiling to the stack.

Each fan coil has condensate line, which needs to be sloped too.

The worst case scenario is where a sloped pipe needs to run under a duct: here, there are two depths in one place and the ceiling needs to sag enough to go over both of them.

If it is foreseen beforehand, then it is done as sloping pipe in the space assigned, but if it is discovered afterwards, then it will show up as a soffit being dropped or stain on the wall of the finished gallery above a year later.

Late MEP work does not change a building’s function.

It changes its look, and rarely for the better.

Why does coordinating MEP late cost more?

The same change is progressively more expensive as the project moves through each phase.

A simple line edit to reroute the ductwork in schematic design changes into a coordination note in design development, to a multilayered revision in the construction document phase, and to an RFI, change order, and obvious compromise in the field.

Here we see the MacLeamy curve at work, the industry’s basic model of design timing where the later the project is, the more costly the change and the less influence there is on the result. The task stays the same for all phases, just the cost and impact grow.

What should an architect ask the MEP engineer for at each design phase?

There are three deliverables that need to be delivered at each phase, one at each phase, protecting decisions the re-visitation of which becomes progressively expensive:

• Schematic Design: system selection discussion.Decide on the system type and its spatial requirements before ceiling heights, shafts and massing are decided. This is the time when the decision is most impactful and low cost on the MacLeamy curve.
• Design Development: shaft and plenum planning.Allocate the space required for ducting, condensate drains and mains before finishing up the reflected ceiling plan.
• Construction Documents: a coordination pass before locking the permit set.Coordinating the trades by overlaying the drawings in advance allows identifying clashes on paper and fixing them through a drawing change as opposed to an RFI.

Ask for these three deliverables and you get your engineering fit into the architectural scope at each phase, and not as a revision at a later phase.

The recommendation. Bring the MEP engineer at the schematic phase and not at the permit set phase; the one decision alone will decide whether the systems complement or hinder your design. In a coordinated project, the owner doesn’t see the engineering process.

We work with architects from the schematic phase under our Integrated MEP Design service. The earlier we are at the table, the less the systems fight the design. If you are starting a project, bring us in at the sketch stage.

Sources: Patrick MacLeamy — cost/impact curve (the cost of late design changes) · IPC 704.1 — slope of horizontal drainage piping · Condensate drain slope — 1/8″ per foot minimum · ASHRAE 169 — climate zone 1A