Project: Heritage building redevelopment, roof retention during demolition and structural steel installation
Location: NSW
Sector: Commercial construction / heritage redevelopment
Client: Royal Group NSW
Services Provided: Temporary works propping design input, equipment supply & installation.
Equipment Used: Legend Multiprops, scaffold tube and fittings, base plates and sole plates
The Challenge
The heritage roof, a timber truss and rafter structure carrying profiled metal sheeting was to be retained while the structure supporting it was removed. Once demolition began, the roof’s original load path to ground no longer existed. Without a temporary system in place, the roof would have been left carrying its own dead load, and any imposed wind load, on elements scheduled for removal.
Three constraints shaped the solution:
- Retained heritage fabric. Aged timber members and masonry walls could not be modified, drilled or overloaded to suit the propping layout. The system had to work around the existing structure rather than through it.
- Working space beneath. Contractors, demolition plant, elevated work platforms and steel erection all had to operate below the retained roof. A dense prop grid would have supported the roof and stalled the programme.
- Sequencing. The propping had to remain stable through every stage, before demolition, during removal of the original supports, and while the new structural steel was erected and loaded.
Engineering Considerations
Temporary propping of a retained roof is a load-transfer problem, not simply a matter of installing vertical supports. The system must pick up roof loads at the existing bearing points, carry them through props of adequate capacity, and distribute them into a slab or foundation capable of receiving them, while remaining laterally stable in isolation, because the surrounding structure that once provided that restraint is being removed.
Key considerations on this project:
- Prop grid and spacing were set by the roof’s existing bearing lines, so loads were picked up where the structure was designed to carry them.
- Lateral stability was provided by scaffold tube bracing in both horizontal and diagonal planes, tying the props into a stable frame. This is the critical detail: unbraced props of this height are slender elements vulnerable to buckling once adjacent structure is removed.
- Base bearing was checked against the existing slab to confirm point loads could be accepted without local failure or punching.
- Access corridors were designed into the grid layout from the outset rather than opened up after installation.
The Solution
Legend Hire installed Legend Multiprops beneath the retained roof structure, set out on a grid aligned to the existing bearing points and adjusted to bear directly against the roof framing.
Each prop line was braced with scaffold tube and scaff tube couplers, forming a horizontally and diagonally braced frame across the full footprint. This converted a set of individual vertical props into a single stable structural system capable of resisting lateral load once the original supporting structure was removed.
The grid layout was set out to preserve clear working corridors beneath the roof, allowing scissor lifts, demolition plant and steel erection equipment to operate throughout the works without dismantling or relocating props.
Installation was coordinated with Royal Group NSW site team and staged so that the temporary system was fully installed, braced and verified before any load-bearing demolition commenced.
Equipment Used
- Legend Multiprops: high-capacity adjustable propping for the primary vertical load path
- Scaffold tube and fittings: horizontal and diagonal bracing for lateral stability
- Base plates and sole plates: load distribution at slab level
The new structural steel now carries the roof permanently, and the temporary system was progressively de-propped and removed once the permanent load path was established.
Frequently Asked Questions
A heritage roof is supported by installing a temporary propping system that creates an alternative load path to ground before the original supporting structure is removed. Props are set out on the roof’s existing bearing lines, braced laterally to resist buckling and sway, and founded on a slab or footing verified to accept the imposed point loads.
Individual props are slender vertical elements. Once the surrounding structure that provided lateral restraint is demolished, unbraced props are vulnerable to buckling and sway. Scaffold tube bracing ties the props into a stable braced frame, allowing the system to stand independently of the structure being removed.
Yes, provided the prop grid is designed around the required access and plant movements from the outset. Setting out clear working corridors during design avoids the alternative of relocating props mid-works, which reintroduces risk at the worst possible moment.
Legend Multiprops are typically used for retained roof structures where high capacity and adjustability are needed, combined with scaffold tube bracing for lateral stability and base plates to distribute load at slab level. Selection depends on the roof’s bearing arrangement, prop height and the capacity of the supporting slab.