You drive past another property for sale, claiming the site is perfect for a multi-unit townhouse development, STCA.
STCA means "subject to council approval" and it also means the site doesn’t have a planning permit, so good luck with the townhouses.
A planning permit is the end result of a process concerned with the use of land and design of the urban environment. It is a process that addresses both technical and political considerations, making it a fertile arena for a plethora of stakeholders, both real and confected.
In fact, arguments over town planning decisions date back to the 5th century BC, with Aristotle’s critique and apparent ridicule of Hippodamus (regarded as the first town planner) being perhaps the first known example of a criticism of urban planning.
Planning covers a very broad range of issues, but is essentially about the decisions that change the environment and affect everyday life. Planning also has economic significance as a site with a town planning permit in place is often sold for significantly more than the same site without.
The selling of a site with a town planning permit offers certain benefits. For instance, a town planning application does not require engineering documentation – these are required for the building permit.
It doesn’t take us long to identify which projects have had engineering input to validate and prove the design submitted for Town Planning, and those that don’t.
Here is a list of things that should be looked at and understood before the town planning submission.
- Establish the location of existing authority services around the site and through the site. Relocating authority services is a time consuming exercise, not to mention an expensive one. Authority services relocation is always a below the line item of any preliminary cost estimate and is not included in square metre rates used for construction costs.
- Establish the capacity of the existing authority services. Once again, if an electrical substation is required, not only will it have a cost impact, but the spatial requirements can be significant, and non-negotiable access requirements can really mess with planning layouts if not initially allowed for.
- If the project involves any significant basement excavation, allow an absolute minimum of 675 millimetres for the permanent/temporary retention structure. This provides for a 600-millimetre diameter bored pier and for the (Australian Standard permitted) 75 millimetre out of position of a pile to occur, without the pile, at least theoretically extending outside the property boundary. Be wary of anyone who says 450-millimetre piles will work (they are very inefficient) and if mechanical ventilation of the basement is required additional allowance for a plenum along the retention system (between 600 millimetres and 1,000 millimetres) should be made.
- Get a copy of Australian Standard AS/NZS 2890.1, and use it to set out your car parking spaces, aisles and turnouts. It also provides areas where obstructions are prohibited so that car doors can be opened, so use this to set out your column layout.
- If the development is commercial in nature, try to run the basement column grid throughout the building. The aim is to create a structural framing system that doesn’t need transfer structures. Transfer structures are perfectly acceptable structural solutions, but they tend to make basements deeper if they are needed below ground level, or make buildings taller if required above ground. Either way, transfer structures have cost and construction program implications.
- If the development is residential, it is likely that the carpark column grid will not be compatible with a grid established using load bearing walls between discreet residences. If this is the case, allow for the increased depth of the transfer plate. Typical floor plates without transfers are generally between 200 and 250 millimetres thick. Transfer structures can vary from 500 to 1,000 millimetres deep or more. If you have pushed your building envelope to the height limit allowed, and haven’t made provision for this extra depth, the client is going to be very unhappy! The compromise solution invariably means less rentable or saleable area.
- Try to keep vertical elements such as walls and columns aligned. This is generally an issue when the apartment mix of successive floors changes, resulting in load bearing walls over and under that do not align. That’s another transfer level.
- Consider the services required for the building, and how they will be reticulated. Whilst building service engineers are known for asking for large service risers, this is often in response to often being forced to squeeze services into unusable or inaccessible locations. These are the building components that traditionally provide the most problems during the working life of a building, so take a long-term view about maintenance access and ease of replacement.
- Stacking services so that reticulation is vertical rather than horizontal is much more efficient, particularly for services that rely on gravity.
- Having coordination workshops before the town planning submission, involving the architect, the structural engineer and the building services engineer will always result in a better solution.
- A preliminary lateral stability analysis will provide advice as to the required thicknesses of corewalls and stair shaft walls. Whilst the probability of earthquakes in Australia is low, the Australian Standard still requires most structures to be designed for a one in 500 year event
The town planning process doesn’t require the submission of engineering documentation, so many developers do not engage engineers for the town planning submission. If you are one of these, at least consider the points above so that whoever has to document the project has a fighting chance of the end result aligning with original submission.
At the very least, don’t go to marketing and sell apartment spaces until some engineering is done. I am aware of one instance where an apartment purchaser was told a column was required in his living area. He said “No, not in the apartment I bought!” Lawyers love this stuff.
Adequate engineering input into the town planning process isn’t expensive, and will always produce a more holistic design. Better outcomes will be achieved when a design is moderated and refined by a professional and comprehensive consulting team.