Heritage Facade Retention, Demolition and Basement Excavation, Broadway, Sydney

Status: completed October 2024. Client: Tier 1 client (confidential). Location: Broadway, Sydney. Scope: internal demolition of a four level heritage building behind its retained brick facade, then excavation of a two level basement through sandstone, with underpinning, rock sawing and detailed excavation around the facade retention steel.

The client engaged Perfect on two packages on a heritage site at Broadway. The first was the demolition: a four level brick building where the external facade had to stay standing while the timber floors, roof, lift shaft, four level fire stair and internal spine wall all came out. The second, won on a separate tender after the demolition was under way, was the excavation: two basement levels, a wine cellar and a lift shaft cut down into sandstone inside the footprint the facade left us. About 2,600 cubic metres of ground in total, most of it rock.

What the job involved

• Internal demolition of a four level building behind a retained brick facade: timber floors, roof structure, lift shaft, four level fire stairs and the internal spine brick wall
• Working around the facade retention steel installed by the client's specialist subcontractor, with the retained brickwork dictating the order of everything next to it
• Slow initial excavation of the top 500 mm of fill with an archaeologist on site to inspect the material
• Underpinning of the boundary footings in sections to about 1.2 metres, with saw cutting of the old brick and concrete footings, formwork, reinforcement, concrete and dry packing
• Bulk excavation of about 2,200 cubic metres, from sand through low, medium and high strength sandstone
• Detailed excavation for pad footings, strip footings, a lift pit and two car lift pits, plus trenching for the sub floor retention steel
• Rock sawing and wire sawing next to retained structure to keep vibration off the heritage walls
• Load out through the building by skip bin and direct to truck muck bins on the client's tower crane, with no stockpiling on site
• Spoil classified before it left site, with dockets and monthly waste reporting to the client

What made it hard

The facade set the rules. Every brick of the street and side frontages had to stay, so the building was taken apart from the inside working inwards, with an internal steel retention frame installed before any structural demolition. Nothing was propped off the street. Once the floors were gone the same walls, now standing on their own footings above a hole, had to be underpinned before the dig could go below them.

Then the ground. Under a shallow layer of fill and sand the site is sandstone, and a lot of it is high strength. Breaking it with hammers a metre from a heritage wall is not an option, so the rock was sawn into blocks and lifted out, with hammers used only away from the boundaries. Along the cellar boundary a 1.2 metre wide strip was taken out with a remote controlled demolition machine and wire sawn so the retained structure was never touched.

Access was the third problem. Once the first level was down there was no ramp and no room for a truck. Compact excavators were lifted in and out by the client's tower crane, and everything that came out of the hole went up in muck bins on the crane hook and straight into trucks in the loading window on the street.

How it was run

The demolition ran from June to October 2023 under a demolition licence and a SafeWork notification, with the heritage facade the only thing left standing when the excavation package started. The excavation ran under a written excavation management plan that set out the sequence: pre planning and services, site establishment and protection of the retained structure, the slow archaeological dig, underpinning, then bulk and detailed excavation working from the laneway end so the client could get the first tower crane base in early.

Working hours followed the consent, with high noise work confined to the middle of the day and the respite periods respected. Sediment and water were pumped and managed within the excavation. Every load off site was classified and docketed, and a waste table was reported to the client every month.

How it went

The facade is still standing and the new building is going up behind it. Perfect handed over a two level basement cut to level in sandstone, with the underpinning done, the lift pit and car lift pits in, and starter bars set for the new structure. The client had us back on the site in 2025 for a further package of works.

If you have something similar

Heritage frontages, retained walls, tight inner city sites and rock under the floor are the jobs Perfect Strip Out and Demolition does most. If you need a building opened up behind a facade and dug out underneath, have a look at our demolition, detailed excavation and underpinning pages, or the partial demolition and propping page. Otherwise just get in touch and tell us what you are dealing with.