Extraordinary Council Meeting
24 May 2016
Subject: Proposed Tree Removal - 2 Vincent Street, Marrickville
File Ref: 16/4718/56921.16
Prepared By: Neil Strickland - Director Infrastructure Services, Marrickville and Wal Petschler - Manager Design and Investigation, Marrickville
Authorised By: Vanessa Chan - Interim General Manager
At its April 2016 meeting Council deferred consideration of removal of a tree on the footpath verge at 2 Vincent St, Marrickville to enable investigations to be completed by Council staff concerning alleged tree root damage to the adjacent building. Exploratory excavation undertaken could not substantiate tree roots as the cause of building defects.
1. the tree adjacent 2 Vincent Street, Marrickville be retained; and
2. the matter be subject to further review should conclusive evidence be presented demonstrating the tree to be the primary cause of property damage.
At its meeting of 19 April 2016, Council considered a notice of motion for the removal of a mature tree on the footpath verge fronting No 2 Vincent Street, Marrickville and its replacement with a more appropriate planting. Removal was proposed based on damage to the adjacent building allegedly caused by tree roots.
Council resolved that “the elected Council expresses its concern and requests a report to the next Council Meeting about a street tree outside 2 Vincent Street Marrickville and requests that Council consider replacing it with a more appropriate planting as a matter of urgency.”
The cost of tree removal, replacement and establishment is estimated at $2,500 and could be completed within existing operational resources.
The value of this tree to the streetscape and public domain is estimated at $55,000 based on the industry recognised THYER valuation method. This methodology places a value on the tree’s significance, health and condition, age and life expectancy, size, environmental and social benefits.
OTHER STAFF COMMENTS
The tree in question as depicted in the photo below is a fully mature Corymbia citriodora (Lemon Scented Gum) in good condition with no known structural defects and a Usable Life Expectancy (ULE) of 20+ years. It is considered a highly valuable street tree that contributes significantly to the urban canopy and visual amenity of the streetscape which is defined by an avenue of these trees.
Photo 1: Existing Lemon Scented Gum
An engineer’s report prepared in 2015 attributed damage to the building to tree roots emanating from the adjacent tree. This conclusion was reached based on visible damage caused to the adjacent public footpath illustrated in the Photo 2 below taken from the engineer’s report.
Photo 2: Footpath leading to property
To complete a more detailed investigation of the likely contribution of tree roots to the property damage, Council officers removed the concrete path and undertook exploratory excavation by hand adjacent the building and the two driveways. Trenches adjacent these structures were dug to a depth until hard compacted clay subsoil was encountered or to expose the base of the building footing or driveway slabs.
Photo 3: Footpath removal adjacent tree
Photo 3 shows evidence of roots located under the public footpath which caused the lifting and damage to the concrete path shown in Photo 2. However the excavations did not reveal any visible evidence of tree roots extending to or under the building. The trenched areas were largely devoid of tree roots. Only one 30mm diameter root was uncovered running alongside the building footing. This has been cut approximately 2.5m from the building as a preventative measure.
Photo 4: Excavation adjacent doorway
Whilst an indirect contribution of the tree towards cracking/ movement of building elements cannot be categorically ruled out there is no evidence demonstrating it to be the primary cause. Other causes such as structural loading of the slab/footings may be the predominate contributor to the defects referred to in the engineer’s report.
Based on the available evidence the need to remove such a prominent tree cannot be substantiated. Should the property owner propose to undertake defect rectification of the internal slab in accordance with the engineer’s recommendation, further confirmation of the presence or absence of tree roots under the building can be undertaken following excavation of the defective slab.
There has been no public consultation to date. It is desirable that Council publicly notify its intention to remove such a significant tree prior to initiating works as is normal practice.
Based on the information presented to Council and Council’s own exploratory excavation and investigations there is insufficient evidence to identify the tree as the primary cause of building defects. As its impact on the adjacent property is unsubstantiated, the removal of such a high value tree is not recommended at this time. The matter can be further considered should conclusive evidence be presented demonstrating the tree to be the primary cause of property damage.