When the roots of street trees were suspected of causing damage to a building at Alexandria occupied by Opera Australia, the City of Sydney commissioned Costin Roe Consulting to investigate and report.

Like most suburbs of inner Sydney, Alexandria showcases streets lined with trees of considerable size and age. The narrowness of inner-Sydney streets will often mean that trees, only small when first planted, have reached maturity within close proximity to residential buildings and commercial properties.

Tree roots Opera Australia building

Large street trees grow in close proximity to the Opera Australia building in Alexandria, Sydney. The encroachment of tree roots is a common problem in densely built inner-city areas.

The City of Sydney values the trees on Sydney’s public and private land as public assets. The city’s Urban Forest Plan 2013 commits to a sustainable Sydney by 2030 and ongoing improvement in the diversity of the urban canopy. So, when trees become a problem for the built environment, remedial works must be undertaken with great sensitivity, and in close consultation with the City Of Sydney. Costin Roe Consulting are experts at devising remedial engineering solutions where commercial requirements and stakeholder interests need to be managed within the broader context of environmental preservation.

At 58-66 Euston Road, Alexandria, a commercial property occupied by Opera Australia, Costin Roe Consulting found that the roots of two large trees, growing in the street outside the building, had penetrated the ground beneath the basement floor slab.

Just below the front entrance to the building, the basement floor slab had lifted by approximately 100mm over an area of 8 metres x 3 metres. The investigation also revealed that tree roots were blocking an in-ground cast iron stormwater pipe connecting the building downpipe and the street gutter.

Remedial works recommended by Costin Roe Consulting included the removal and replacement of the affected concrete slab, tree root pruning, and the installation of a root barrier to prevent further root growth beneath the floor slabs in the basement car park. To clear the blocked stormwater pipe, tree root coring was recommended, or alternatively the replacement of the blocked section of pipe.

Tree roots Euston Rd Alexandria

Roots were blocking an in-ground stormwater pipe.

Tree roots lifting concrete slab

Two trees roots in excavation outside the storeroom wedged between two concrete slabs, lifting the top slab.