How Drawing Review Caught 412 MEP Clashes on a Houston Hospital

87 Above-Ceiling Clashes in an 18-Inch Hospital Plenum

An MEP subcontractor had the mechanical and plumbing scope on a 180,000 SF hospital expansion. The plenum above the ceiling was about 18 inches, and it had to hold ductwork, piping, cable trays, medical gas, and pneumatic tube.

Medical gas crossed the HVAC trunk ducts in several patient corridors. The plumbing riser did not pick up transfer beams added in the latest structural revision. Isolation-room exhaust sizes on the mechanical plans did not match the infection-control narrative in the specs.

Estimating had already flagged the risk at bid. They still needed a count of the conflicts before they locked the price.

Helonic Found 43 Medical Gas Routes Through Structure

They uploaded the MEP set with the reflected ceiling plans and the structural framing plans. The check focused on above-ceiling space, medical gas routes, and infection-control exhaust.

Helonic returned 412 coordination issues. The severe ones clustered in three places: 87 above-ceiling clashes where duct, pipe, and tray occupied the same space, 43 medical gas routes through structure or duct, and 29 exhaust systems that did not match the required pressure relationship.

The rest were plumbing stack conflicts, electrical panel clearances, and fire dampers that could not be reached for maintenance.

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$180,000 in Field Conflicts Kept Out of the Ceiling

The subcontractor took the list to the next OAC meeting as one coordination log, instead of raising each clash in the field. Design changes at that point cost a fraction of a finished ceiling.

They estimated $180,000 in avoided field work, mostly medical gas that would have meant core drilling, and above-ceiling rework that would have forced a re-inspection of infection-control barriers.

The same log set the contingency in the contract and put the design conflicts on the design team, not on the subcontractor as a field fix.

The exhaust mismatch between the mechanical plans and the specs is a common pattern. Across 1,000+ drawing packages Helonic has reviewed, about 6 in 10 sets with specifications had at least one conflict between the drawings and the project manual. See submittal review time benchmarks.

NFPA 99, ASHRAE 170, and the 43 Medical Gas and 29 Exhaust Findings

Hospital medical gas piping is governed by NFPA 99, the Health Care Facilities Code. It sets how medical gas is installed, zoned, labeled, and tested. A route changed after install means retesting and recertifying the affected zone.

Isolation room exhaust and pressure come from ASHRAE 170, Ventilation of Health Care Facilities, which the FGI Guidelines incorporate. It sets the air change rate and the pressure relationship for each room type. The 29 exhaust findings were rooms where the mechanical sizes could not produce the relationship the infection-control narrative required.

Hospitals that serve Medicare patients are surveyed against NFPA 101, the Life Safety Code. The City of Houston reviews the building permit under its own construction code, based on the International Building Code with local amendments.

The ceiling is where all of those rules meet. An 18-inch plenum has to hold medical gas, exhaust, sprinklers, and access to fire dampers. Each of the 87 above-ceiling clashes was a place where two of them were drawn into the same inches.

“Helonic caught 87 above-ceiling conflicts and 43 medical gas routing issues before we broke ground. Those would have been change orders once the ceiling was closed.”

Houston Hospital MEP Review: Questions and Answers