At Raha Design, we consistently encounter the same mechanical, electrical, and plumbing (MEP) coordination issues on low-rise wood-frame projects across British Columbia.
These are not hypothetical design risks. They are real coordination failures that eventually show up in RFI logs, change order requests, field rework, and schedule delay notices.
All of them can be identified and resolved during preconstruction, when changes are still relatively simple and inexpensive. Once framing is underway, the same conflicts become significantly more difficult and more costly to solve.
Below are some of the most common issues we encounter and what can be done to prevent them.
Missing Structural Support for Mechanical Rooftop Units
Mechanical rooftop units (RTUs, AHUs, HPs, ERVs) carry a significant dead load that must be transferred down through the structure and coordinating that support is routinely overlooked. On many wood-frame projects, the framing is either absent from the structural drawings, or it is not drawn specifically to the project, with no coordination against the actual mechanical layout and equipment weight. Once the framing is up, it could be too late to add proper support at the unit’s intended location.
That intended location matters. Rooftop units are deliberately positioned above common or public areas, away from residential suites or quiet spaces because of the noise they generate. When missing structural support forces a relocation after the fact, the consequences arise:
- A suitable alternative location away from the suites may not be feasible, so the unit ends up closer to where nobody prefers
- The duct layout must be redesigned for the new location, often requiring additional fittings to reroute the ductwork. This increases static pressure and degrades airflow. Additional exterior-grade insulation will be needed which adds a meaningful cost
- If a down-discharge unit was specified to sit directly above the shaft, moving it off the shaft breaks that configuration and forces a switch to a side-discharge unit. That means new fabrication lead time and delivery, which pushes out the construction schedule
None of this is a surprise that can only be found on site. The location of units can be determined, agreed on, and approved early. The equipment load is known, and proper structural support can be easily identified and implemented into structure before it is built to avoid every one of these downstream problems.
Exterior Framing Clashes with Ductwork
Routing HVAC intake and exhaust ductwork through a wood-frame building requires early and careful coordination between the mechanical, structural, and architectural designs.
These ducts are typically large and should be routed as straight and efficiently as possible to minimize pressure loss and maintain HVAC system performance. At the same time, their routing must account for structural headers, beams, framed openings, and joist layouts, while also minimizing the size and extent of architectural bulkheads.
A common issue we see is mechanical ductwork being designed without sufficient coordination with the architectural and structural drawings. For example, a duct may run perpendicular to the joist layout with no corresponding bulkhead shown on the architectural drawings. By the time the conflict is identified, adding a bulkhead may not be acceptable to the owner due to additional cost, reduced ceiling height, or aesthetic concerns.
Similar clashes often occur where intake or exhaust ducts approach exterior wall openings. The intended duct route may conflict with headers, beams, or framing around openings, forcing the ductwork to be offset or rerouted.
These conflicts can significantly affect duct routing, ceiling and bulkhead design, mechanical performance, and construction cost. Coordinating the duct routes with the architectural and structural design early in the project helps identify these constraints before they become field issues and allows all disciplines to develop a more efficient solution.
Rainwater Leaders Routing and Layout
Routing rainwater leaders is always a challenge, and this one is not unique to wood-frame buildings. The rainwater must be collected at the roof and carried down through the building to discharge, and getting those runs to work means solving several competing constraints at once.
What we see instead is a rainwater leader designed at the roof with the interior routing path never mapped through the building. When the piping is not coordinated against structural early, runs drawn as clean straight lines on the 2D drawings turn out to be unbuildable because a structural element sits directly in the path. Now the runs must be divided and every pipe rerouted. The goal often shifts to finding the cheapest fix, which usually contradicts the original design intent. Instead of minimizing wasted space and keeping ceilings as high as architecturally intended, you end up adding unnecessary bulkheads just to clear the obstruction.
The accumulated drop over a long run can eliminate the headroom the design requires and the code mandates, and by the time it surfaces, the pipe is already framed around. This is exactly the kind of conflict that is cheap to solve in the model and expensive to solve on site. Coordinating the routing against the structural model before the drawings are issued lets you:
- Find viable locations for the risers in the first place
- Manage slope on the horizontal runs while still meeting headroom clearances
- Run pipe through areas that do not require a bulkhead, or that waste the least space possible
- Avoid structural elements such as beams, slab bands, and joists along the way
- Eliminate after-pour concrete scanning, cutting, and coring
Before Your Next Wood-Frame Project in British Columbia
If your project is still in preconstruction, this is the best time to identify these coordination gaps, before they turn into RFIs, change orders, field rework, or schedule delays.
Raha Design reviews architectural, structural, and MEP systems together to identify constructability issues before framing begins and help project teams develop practical, coordinated solutions.
Book a session with us to discuss how early MEP coordination can reduce risk before construction starts.