Rooftop Unit (RTU)
CSI Division 23, HVAC
A packaged heating and cooling unit mounted on a building's roof, combining the compressor, coils, and fan into a single factory-built unit that connects to the building's ductwork, the standard cooling approach for most single-story commercial and retail buildings.
Why it matters
An RTU has to be set on a properly engineered curb that both supports its weight and seals the roof penetration around it, so this single piece of equipment sits at the intersection of structural, mechanical, and roofing work, a coordination point where a mistake in any one trade's scope can compromise the other two.
On a real project
A crane sets a new RTU onto a roof curb built to the manufacturer's exact dimensions and structural load requirements, and the roofing crew flashes and seals the curb into the roofing membrane before the mechanical contractor connects ductwork and power.
Who this matters most to
An HVAC Technician sets, connects, and commissions the unit, verifying it operates to its rated capacity before turnover. A Quality Control Manager confirms the curb's structural support and roof flashing details are complete and inspected before the unit is set, since re-flashing under an already-set unit is far harder than doing it right the first time.
Where this goes wrong
A roofing crew flashes an RTU curb using a generic detail rather than the manufacturer's specific curb dimensions, leaving a slight gap at one corner. The gap isn't obvious during a dry-weather walkthrough, but the first heavy rain finds it, and water tracks into the ceiling below before the leak is traced back to the improperly flashed curb.