Site Access, Stormwater and Tree Protection on a Sloping Allotment
You are documenting a new two-storey dwelling on a 900 m² allotment that slopes about 3 m from the street to the rear. The design has a driveway at 1:6 down to a garage cut into the slope at the lower rear corner. A mature eucalyptus stands 4 m from the proposed garage wall, within the root zone. The site drains toward the rear boundary, where a neighbour's dwelling is 2 m lower. The council has requested a site plan showing levels, drainage and tree protection before it will assess the development application. The client wants to keep the tree and the garage in its current position.
1. Identify the site planning and environmental issues that the site plan must address, and explain how you would show them.
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The site plan must address three interconnected issues: access gradient, stormwater discharge, and tree protection. The driveway at 1:6 is steep; depending on the jurisdiction, driveways generally need to be within a maximum grade, often around 1:4 to 1:5 for short sections, with transitions at the street and garage. The plan should show the driveway centreline levels, the grade at each change, and the transition at the garage, so the council can see the access is usable and that vehicles will not scrape.
Stormwater is the second issue. The site drains to the rear boundary where the neighbour is 2 m lower, so concentrated discharge could cause nuisance or damage. The plan should show how stormwater is collected and discharged, for example to a legal point of discharge, an on-site detention system, or a spreader, and should demonstrate that the flow is not concentrated onto the neighbour. Levels at the boundary should be shown.
The tree is the third issue. A mature eucalyptus 4 m from the garage wall is within its root zone, and excavation for the garage could sever roots. The plan should show the tree protection zone, the canopy, the trunk, and the proposed protection fencing, and should demonstrate that the garage excavation does not encroach into the protected zone, or that an arborist has assessed the impact.
2. The client insists on keeping both the tree and the garage in its current position. What would you do, and what would you document?
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I would not simply draw what the client wants. I would explain that the garage position and the tree protection zone appear to conflict, and that council is unlikely to approve the application without evidence that the tree can be retained. I would commission or request an arborist's report to assess the tree's root zone and the impact of the excavation, and I would ask the structural or civil engineer whether the garage can be redesigned, for example by shifting it, reducing its size, or using a pier-and-beam or cantilevered slab to reduce excavation near the tree. If the arborist confirms the tree can be retained with a root barrier or a reduced excavation, that becomes the documented basis for the design.
What I would document: the arborist's report, the client's instruction to retain both elements, the options considered and their cost or feasibility, and the agreed resolution. If no resolution is possible, I would record that the design cannot proceed as instructed and seek a written direction. The site plan submitted to council should reflect the resolved design, not an unresolved conflict.
3. Outline the content you would include on the site plan for the development application.
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The site plan should include: the allotment boundaries and dimensions, the north point and scale; the existing and proposed contours or spot levels, including the 3 m fall across the site; the proposed dwelling footprint, garage, driveway with centreline levels and grades, and any retaining walls; the stormwater strategy, including pits, pipes, on-site detention, the legal point of discharge and overland flow paths; the tree protection zone, canopy and fencing for the eucalyptus; the neighbour's dwelling and relative levels at the rear boundary; and the setback dimensions to all boundaries. It should also show the street frontage, crossover and any easements.
I would add notes referencing the arborist's report, the stormwater design and the driveway grade, and I would show the finished floor level of the dwelling relative to the site and the street. The plan should be drawn at a standard scale, with a title block, revision and date, and it should be checked against the architectural and civil drawings so that the levels and dimensions agree. The aim is to give the council a single, consistent document that demonstrates the development can be built and drained without unreasonable impact on the neighbour or the tree.