What Is a Roof Carriage System?
Definition: A roof carriage system is a permanent building maintenance installation in which a wheeled carriage travels along a roof-mounted track or runway and suspends a working platform over the building face. OSHA recognizes carriages as one of the methods for suspending elevated building maintenance equipment, and defines a roof car as a structure for suspending a working platform that provides for its horizontal movement to working positions.
Roof carriage systems sit between davit systems and full building maintenance units (BMUs). With davits, crews must lift the davit arms out of one pair of sockets and reset them in the next for every drop. A roof carriage keeps the suspension points mounted on a traveling frame, so the platform can be moved along the roof track to the next working position without dismantling anything. One common configuration is the powered davit carriage — a pair of traversing carriages, each carrying a davit mast and boom, that run along a roof track and are operated from roof level with a pendant control.
Compared to a full BMU, roof carriage systems are typically simpler and more economical, with smaller carriages and shorter outreach instead of a large roof car with telescopic or luffing jibs. They are well suited to buildings with straight or moderately shaped facades and enough roof space for a perimeter track. Through Scaffold Exchange, you can find companies across the U.S. that design, install, inspect, and service roof carriage systems in your area.
Key Components of a Roof Carriage System
Every roof carriage installation is engineered for its building, but most systems share the same core components working together as a permanent powered platform installation.
Roof Track or Runway
A rail, I-beam, or load-bearing concrete runway installed around the roof perimeter that guides the carriage and carries its load into the building structure.
Carriage
The wheeled frame that travels along the track. Can be manually pushed or powered with motorized drives, and is secured to the track to resist tipping and uplift.
Davit Mast & Boom
A mast and outreach boom mounted on the carriage that positions the suspension wire ropes beyond the building face. Booms may rotate to bring the platform onto the roof.
Suspended Platform & Hoists
A gondola or swing stage with traction hoists, or hoisting winches on the carriage itself, that raise and lower crews along the facade.
Controls & End Stops
Pendant or platform controls for carriage travel and hoisting, with mechanical end stops and travel limits that keep the carriage within its track.
Common Applications & Building Uses
Roof carriage systems are specified for buildings that need regular facade access more often or more efficiently than davits allow, but do not require a full BMU. They are common on commercial, residential, and institutional buildings throughout the United States.
Routine window cleaning on low, mid, and high-rise buildings
Straight and moderately shaped facades with open roof space
Buildings where moving davits between sockets is too slow
Curtain wall glass and panel replacement
Sealant, caulking, and facade maintenance
Periodic facade inspection and condition assessments
Upgrading existing davit installations for faster access
Projects where a full BMU exceeds the budget or roof capacity
How Roof Carriages Compare to Other Permanent Access Systems
Roof carriage systems fill the middle ground of permanent facade access. Here is how they compare to other permanent motorized access systems and which buildings each suits best.
Permanent sockets with removable davits
- Lower installed cost than carriages
- Davits moved by hand between sockets
- No roof track required
- Best for low and mid-rise buildings
Certified fixed anchor points
- Lowest installed cost of permanent options
- Used with temporary rigging
- Provides lifeline and tieback anchorage
- Best for basic or infrequent access needs
Track-mounted roof carriages
- Carriage travels a roof track or runway
- No davit relocation between drops
- Simpler and more economical than a full BMU
- Best for straight facades with frequent access
Permanent powered facade access
- Large roof car with telescopic or luffing jibs
- Reaches over setbacks and high parapets
- Highest installed cost and roof footprint
- Best for high-rise and complex facades
Overhead trolley track system
- Track fixed at or beyond the building face
- Minimal rooftop equipment required
- Tracks follow curves and run under overhangs
- Best for curved facades and limited roof space
Find Roof Carriage Installers Near You
Use the Scaffold Exchange map to search by location, filter by equipment type, and connect directly with local companies that design, install, inspect, and service roof carriage systems.
OSHA Compliance & Safety Standards
Roof carriage systems used for building maintenance are governed by OSHA standard 29 CFR 1910.66, Powered Platforms for Building Maintenance, which lists carriages among the approved suspension methods and sets specific requirements for carriages used to suspend elevated building maintenance equipment. Design and installation also follow ASME A120.1. Building owners and employers share responsibility for keeping the track, carriage, and platform inspected, tested, and safe to use.
- Installation inspected and tested before initial service and after major alterations
- Carriage secured to the track against tipping and uplift
- End stops and travel limits at both ends of the track
- Building owner certifies in writing that the system is inspected and maintained
- Personal fall arrest tied to an independent lifeline anchorage
- Periodic inspections by a competent person per manufacturer intervals
1910.66
Powered Platforms for Building Maintenance — U.S. General Industry Regulations
OSHA Interpretations & Rulings →