Planning a Rooftop HVAC Replacement on a Houston Commercial Building
On most Houston office, retail and flex buildings, the air conditioning sits on the roof. When rooftop units reach the end of their life, owners usually focus on the equipment: tonnage, efficiency and brand. But a rooftop replacement is also a roofing project, a structural question, a crane operation and a tenant-coordination exercise. Missing any of those pieces can turn a straightforward swap into leaks, delays and change orders.
This guide covers the building side of a rooftop HVAC replacement so owners and facility managers can plan the whole job. It is general information. Your mechanical contractor and engineer should design the equipment selection and system changes.
Why the building side matters
New rooftop units often differ from the old ones in size, weight, curb dimensions and connection locations. A replacement that looks like a one-for-one swap may require:
- A curb adapter or a new curb.
- Roof membrane and flashing work around the curb.
- Structural review if the new unit is heavier or sits in a different spot.
- New electrical, gas or condensate connections.
- Changes to ductwork below the roof deck.
Planning these items before ordering equipment avoids surprises on lift day.
Step 1: Inventory the existing units
Start with a roof survey. For each unit, record:
- Location on the roof and the space it serves.
- Model, age and condition.
- Curb type and condition.
- Roof membrane condition around the curb.
- Gas, electrical and condensate connections.
- Access for cranes or helicopters.
Units that serve critical tenants or server rooms should be prioritized and planned with backup cooling.
Step 2: Coordinate with the roof
The roof around a rooftop unit is one of the most common leak points on a commercial building. If the roof is near the end of its life, consider coordinating the HVAC replacement with a roof replacement so curbs can be properly flashed into the new system. If the roof is newer, your roofing contractor should handle curb flashing to protect the roof warranty. The City of Houston publishes requirements for a commercial roofing permit where roof work is part of the project.
Our guides to flat roof options for Houston commercial buildings and TPO vs. modified bitumen for low-slope roofs explain the membranes most often found under rooftop equipment.
Step 3: Check the structure
A heavier unit or a unit moved to a new location may exceed what the roof framing was designed to carry. A structural engineer can review the roof joists or beams and design reinforcement if needed. Structural changes generally need permits and inspection. Even when the weight is similar, deteriorated decking around old curbs is common, especially where leaks have gone on for years.
Step 4: Plan the crane lift
Most rooftop units are set by crane. Planning includes:
- Choosing a crane location with adequate ground support and clearance from power lines.
- Getting street or parking lot closures if needed.
- Scheduling the lift early in the morning or on a weekend to limit disruption.
- Protecting the roof surface along the path from the drop zone to the curb.
OSHA's cranes and derricks in construction page summarizes safety requirements for crane operations, including power line clearance and qualified personnel. Crane work should be performed by experienced, qualified operators and riggers.
Step 5: Protect workers on the roof
Rooftop work involves fall hazards at roof edges, skylights and openings. OSHA's fall protection resources cover guardrails, safety nets and personal fall arrest systems. Make sure your contractors have a fall protection plan, particularly on roofs without parapets.
Step 6: Understand refrigerant rules
Replacing rooftop equipment involves recovering refrigerant from the old units. The EPA's Section 608 program requires technicians who handle refrigerants to be certified and sets rules for refrigerant recovery, recycling and reclamation. The EPA's Technology Transitions program is also limiting the use of certain high-impact HFC refrigerants in new air conditioning and refrigeration equipment, which affects the refrigerants available in new units. Ask your mechanical contractor how these rules affect your equipment choice and future service.
Step 7: Coordinate tenants and timing
Houston summers make cooling outages a serious issue for tenants. Plan replacements for spring or fall when possible. For each unit:
- Notify tenants of the outage date and expected duration.
- Arrange temporary cooling for critical spaces.
- Coordinate interior ceiling access for duct and thermostat work.
- Schedule after-hours work if required by leases.
Our guide to after-hours commercial construction in Houston explains how to plan work around occupied buildings.
Step 8: Consider efficiency and controls
Replacement is the time to improve efficiency. ENERGY STAR's resources for commercial buildings help owners benchmark energy use and identify improvements. Modern controls, economizers and building automation can improve comfort and reduce energy use. Your mechanical engineer can evaluate options.
Step 9: Bid and phase the work
If you have many units, phase replacements by age, condition and tenant priority. A clear scope that separates equipment, roofing, structural, electrical and crane costs makes bids easier to compare. Our commercial bid comparison guide and capital projects for property managers cover phasing larger work.
Frequently asked questions
Can the new unit go on the old curb?
Sometimes, with a curb adapter. Your mechanical contractor can confirm compatibility.
Do I need a structural engineer?
If the new unit is heavier, moves location or the deck is damaged, an engineer should review the structure.
When is the best time to replace rooftop units in Houston?
Spring and fall usually create the least disruption for tenants.
Planning rooftop equipment replacement and the roof and structural work around it? BPC Development LLC provides free on-site estimates in Houston, TX. Call (281) 301-4737.