Two roof levels, one safe route across.
Roofs step. A mechanical penthouse sits higher than the main deck, an addition was built at a different elevation, a parapet runs between two areas that both need servicing. The way most people get across is a scramble — and the fix is a crossover built to the rise your building actually has.
Short answer: a roof crossover is a stair-up, platform-over, stair-down structure that connects two roof levels or bridges an obstruction. Two-way units have stairs at both ends; one-way units have stairs at one end and a working platform at the other. The rise is site-measured, not catalogue, and on a warranted roof the whole thing is usually ballasted and non-penetrating.
The three problems a crossover solves
- A level change between roof decks. A penthouse, an addition, or a stepped roof leaves two working areas at different elevations, connected by nothing but a parapet somebody climbs over.
- An obstruction in the walking route. Ductwork, refrigerant lines, gas piping, or conduit crossing the path between the hatch and the equipment. People step on it, which is bad for the duct and worse for the person.
- A route that crosses the membrane. Even with no obstruction, repeated foot traffic on a single line across a roof wears the membrane. A defined walkway with a crossover at the level change protects both the roof and the person.
One-way or two-way
The distinction sounds trivial and drives the whole layout:
| Configuration | Shape | Used for |
|---|---|---|
| Two-way crossover | Stair – platform – stair | Linking two roof levels; crossing a duct run |
| One-way platform | Stair – platform | Service deck at a unit; the platform is the destination |
| Walkway + crossover | Run with a crossover in it | Long routes from hatch to equipment |
Most roof-level-change requests are two-way, because both sides of the step are places people need to be. If only one side matters, you may not need a crossover at all — a platform and a single stair is cheaper.
Why stock units rarely fit a roof
Crossovers are sold as standard products, and on a flat factory floor over a fixed-height conveyor they work well. Roofs are different in three ways that matter:
- The rise isn't a round number. A level change between two roof decks is whatever the building was framed to, plus insulation, plus the roofing build-up. It is almost never a catalogue increment.
- Both landing surfaces slope. Roofs are built to drain. A crossover has to land flat and stable on two surfaces that are each pitched, often in different directions.
- What's underneath varies. The bearing condition changes across the roof depending on where the joists and the drains are.
The consequence of forcing a stock unit is shimming — and a shimmed base on a membrane roof rocks, abrades, and eventually becomes the thing that damages what you were trying to protect. Site-measured fabrication costs little more on a one-off and lands flat at both ends. Same reasoning as ship's ladders, where the real rise almost never matches a catalogue.
Exterior detailing: what changes on a roof
- Treadsgrip-strut — sheds snow and ice
- Guards42" with toe board
- Handrailsboth sides of every flight
- Finishhot-dip galvanized
- Field assemblybolted, no site welding
- Drainageno damming, no ponding under
- Bearingmembrane-compatible pads
Two of those are worth dwelling on. Open treads are not optional outdoors — a solid plate tread on a roof in February is an ice tray, which is exactly why grip-strut is the default (the comparison is in grip-strut vs bar-grate). And galvanizing means detailing for bolted field assembly, because field welding burns the zinc off the coating you just paid for — see galvanized vs painted.
How it attaches — usually, it doesn't
The load path is the first question we ask, ahead of dimensions. If the building has an active roof warranty — nearly every municipal, institutional, and recently re-roofed commercial building does — the answer is a fully weighted, non-penetrating system: engineered ballast on membrane-compatible pads, with nothing passing through the roof assembly. The ballast is sized against wind uplift with a safety factor, and increased at roof corners and edges where wind pressure is higher. The full method is in rooftop steel with no roof penetrations.
The alternatives are curb or sleeper mounting with the roofer detailing flashing, or structural anchoring into the framing below. Both are legitimate; both are roofing scopes with warranty implications, and both need the roof structure checked either way — a ballasted system adds permanent dead load, and an anchored one concentrates it.
What we need to quote one
Photos from both roof levels, the measured height difference, what's in the way between them, the membrane type, and how often people cross. That's enough to lay out the configuration and price it. If there's an active roof warranty, tell us who holds it — we'd rather confirm the pad detail with them up front than after fabrication.
We design, fabricate, and install as one scope — stamped drawings, our Ontario shop, our own install crew, and we coordinate the roofer and the crane. More on rooftop platforms & crossovers, or start from contact.