Roof platforms, catwalks and walkways

Purpose and types

Modern industrial roofs carry air-handling units, condensers, exhaust fans, solar inverters and ductwork. These need a structure that transfers their weight to the frames rather than to the sheeting, and safe routes for the people who service them. Three related elements are used:

• Roof platforms – steel frames on top of the roof, supported by posts that pass through the sheeting to the rafters or to purlins designed for the load, carrying equipment and a working area.
• Catwalks – narrow elevated walkways, either on the roof or suspended inside the building beneath the rafters, used to reach equipment, lighting, cranes or ventilators.
• Roof walkways – low-level walkway panels fixed to the sheeting ribs or seams, defining a protected path and spreading foot traffic.

Loads and sizing

Equipment weights not known at design stage should be allowed for as a collateral or concentrated load – see collateral loads. Wind on the equipment and the platform itself, including uplift, must also be carried to the frames.

Structure and roof penetrations

Platform posts are best located over the rafters, where a short stub column with a base plate is bolted to the rafter flange. Where posts fall between frames, dedicated support beams spanning between rafters are added; ordinary purlins are rarely sized for concentrated equipment loads. Every post that passes through the roof needs a watertight detail, usually a factory-made roof curb or pipe flashing that lets the sheeting move with temperature.

• Keep platform decks at least 300–600 mm above the roof to allow inspection and cleaning of the sheeting beneath.
• Use open grating where rain, light and air should pass through; checkered plate where small items could fall.
• Isolate vibrating equipment with mounts so that vibration does not reach the purlins and sheeting.
• Provide a dedicated access route – an internal ladder and roof hatch or an external stair – rather than walking across fragile panels.

Internal catwalks hung beneath the rafters are supported on hangers or brackets from the frames, never from the purlins alone, and their loads are added to the frame design as collateral or concentrated loads. Lighting, sprinkler and crane-maintenance catwalks are the most common examples.

Fall protection and access safety

Roofs are a major source of serious falls. Platforms and catwalks need guardrails with mid-rails and toe boards, and skylights along the route must be protected by screens or covers – see skylights. Access ladders, stair details and grating types are covered in staircases, ladders, grating and checkered plate. Applicable rules include OSHA 29 CFR 1910 Subpart D in the United States, provincial OHS regulations in Canada, AS 1657:2018 in Australia and EN ISO 14122 for machinery access in Europe.

Platforms and catwalks from World Steel

World Steel designs and fabricates roof platforms, internal catwalks and equipment supports with the main building, so that the frames, purlins and roof openings are designed for them from the start. Members are hot-dip galvanized or painted to suit exposure, and grating, guardrails and ladders are supplied as part of the accessories package.