HVAC & equipment platforms: carrying the gear, reaching the gear.
Mechanical equipment ends up on a roof or in the air because there's no floor space for it — which means somebody has to design steel that both holds it up and lets a technician work on it. Those are two different problems, and platforms fail when only one gets solved.
Short answer: design an equipment platform to the operating weight (equipment full of water and media, not the shipping weight), get the load into the building's columns rather than its deck wherever the reaction is significant, size the walking surface to the manufacturer's service clearances — not the equipment footprint — and match the access type to how often people actually go up.
Two jobs, one structure
Nearly every mechanical platform is doing both of these, and it's worth naming which one drives your project:
- Support. The steel carries the equipment: dunnage under a rooftop unit, a stand under an air handler, a raised frame that lifts a compressor off a wet floor. Governed by the equipment's weight and bearing points.
- Access. The steel carries people: a guarded service deck around a unit, a crossover bridging ductwork or piping, a walkway connecting several pieces of equipment. Governed by maintenance live load and guard requirements.
A platform that only supports leaves technicians standing on the roof membrane or straddling ductwork. A platform that only provides access has the equipment bearing on structure that was never checked for it. Both show up in the field regularly.
Operating weight is the number that matters
The weight on the truck is not the weight on your steel. A chiller charged with water, an air handler with wet coils and media, a tank with product — all substantially heavier in service than dry. The manufacturer's submittal gives operating weight and, critically, the bearing point locations, and those points are what the framing plan is built around.
- Design weightoperating, incl. fluids & media
- Bearing pointsfrom equipment submittal
- Walking surface live loadmaintenance rating
- Exterioradd snow & wind
- Rotating equipmentdynamic allowance
- Guards1070 mm (42") industrial
- Finishhot-dip galvanized outdoors
If you have the equipment submittal, send it — it answers most of the design questions in one document. If the equipment hasn't been selected yet, we design to a bounding weight and confirm at shop-drawing stage, which is normal on design-build mechanical work.
Where the load goes on a roof
Rooftop is where this gets expensive, because a roof structure is designed for snow and its own weight — not for a concentrated mechanical reaction. Three arrangements, in ascending order of what they demand from the existing building:
| Arrangement | Load path | Typical use |
|---|---|---|
| Curb-mounted | Into deck & joists | Light rooftop units |
| Dunnage steel | Spread across joists / to beams | Mid-weight AHUs, condensers |
| Column-bearing frame | Direct to building columns | Chillers, heavy or rotating gear |
The rule of thumb: the heavier the unit, the further the load has to travel before it's allowed to enter the building structure. Landing a chiller reaction on a joist mid-span is how roofs get damaged. We review the existing framing — joist designation, spacing, beam lines, column grid — before choosing an arrangement.
The fourth option: don't penetrate at all
All three arrangements above put something through the roof assembly. On a building with an active membrane warranty — most municipal, institutional, and recently re-roofed commercial buildings — that can be a non-starter, and the spec will say so directly: fully weighted system, no fasteners through the roof assembly.
The answer there is a ballasted, non-penetrating structure: weighted bases on membrane-compatible bearing pads, with the ballast engineered against wind uplift rather than estimated. It works well for service platforms, walkways, and guardrail, and for lighter equipment; it is constrained by the fact that the ballast itself is permanent added dead load on the roof. The method is covered in rooftop steel with no roof penetrations, and the configurations on rooftop platforms & crossovers.
Clearances: size the platform to the service, not the footprint
The most common design error we're asked to correct is a platform built to the equipment footprint plus a walkway. Then someone has to pull a coil, and there's no room. Manufacturer service clearances — coil pull, tube pull length, filter access, panel swing, control door clearance — are dimensioned in the submittal and they are what the platform plan has to accommodate. Add the walking surface on top of those, typically 30 to 36 inches clear.
Two more that get missed on outdoor work: condensate and drainage, because a platform deck that ponds under a unit becomes an ice hazard every winter, and roof-edge fall protection, since a service walkway that brings people near an unprotected edge triggers guarding requirements independent of the platform's own guards. Facilities working to US standards will find the criteria in OSHA's 1910.28; Ontario projects are governed by the OBC and the OHSA industrial regulation, and we design to both where a client's corporate standard requires it.
Vibration and isolation
Rotating equipment — compressors, fans, pumps — transmits vibration into whatever it's bolted to, and a light steel frame can amplify it. Two consequences worth planning for: the isolators specified by the mechanical engineer need a stiff, flat bearing surface to work against, and the platform's own natural frequency should be kept away from the equipment's operating range. In practice that means a stiffer frame than a strength check alone would produce. It's cheaper to add stiffness at design than to chase a resonance after commissioning.
Choosing the access
Match the access to real service frequency, not to the cheapest option on the drawing:
- Frequent access, tools or parts carried → a proper access stair. Hands-free climbing is the whole point.
- Periodic inspection → a ship's ladder at 50–70°, where the footprint won't take a stair.
- Rare access, short climb → a fixed ladder, caged or with fall arrest depending on height and governing standard.
The trade-offs are laid out in roof access: stairs vs ladders, and the cage-vs-fall-arrest question in fixed cage ladder requirements. Whatever the choice, the connection between the access and the platform is a detail worth drawing properly — a landing that requires a step across a gap is a hazard regardless of how compliant the ladder is.
What we need to quote
Equipment make and model (or the submittal), required elevation, the existing roof or floor framing information, how often it's serviced, and whether it's inside or out. That's enough for a real design and a real number. We fabricate in Ontario and ship Canada-wide; install crews are Ontario. See equipment platforms for how we build them, or catwalks if the job is mostly access between units.