Top 6 Infrastructure Risks For Infill Property Development

Now that you’ve identified a development site and you’re working through your initial feasibility, are you scratching your head on what the civil costs and implications might be?

It’s frustrating depending on who you speak to and no one seems to want to give you a straight answer and opinions vary wildly.

The following is a checklist of the main issues we regularly encounter that need to be considered as some of them are definitely going to form part of your development and some might also arise which could affect your design and scheme considerably.

1. Stormwater Discharge

You will need to design an appropriate solution for stormwater discharge. If you are creating a higher degree of density than what is currently there, typically council will require some form of stormwater management solution such as detention or retention from your development so this does not place an extra unacceptable burden on the stormwater network.

2. Connections

If you are increasing the number of dwellings on a particular site, you will be responsible for providing new connections for each lot (or dwelling). A charge is payable and depending on the number of units proposed, a suitable design solution will need to be provided.

Capacity assessment will be conducted on the network and this is assessed based on the number of units you are proposing and the age of the network and the impact you will be having on it. It may involve additional costs to assist with the upgrade of the system as you are placing extra load on the network.

Furthermore, in order to make a new connection to an existing network, it's important to find the most suitable location. It could be on public council land or on a neighbouring privately owned property.

If it’s the latter, then the responsibility for obtaining consent from the neighbouring owner falls on the developer and is a civil matter for. If this proves unsuccessful, there is a provision in the Local Govt Act to obtain a right of entry but this not encouraged as it is both costly and slow.

3. Pipelines

If you find a pipeline like a stormwater or wastewater main running through your property, you need to know where they are, how big they are and what impact if any they have on your site. If these are public mains which you can identify

Another good source of locating any is to obtain a copy of your property file from council which should provide drainage plans of your property.

If the pipes cross along your property and underneath where you intend to build, then you will need to submit a works over application and an appropriate bridging solution to ensure the network is not damaged as a result of your development.

It is a costly exercise to divert installed pipelines, but in order to make some developments work, it could be the only solution whether Watercare would approve it.

4. Flood Risk

If your property is in an area that is prone to flooding you will need to get a flood assessment done on your property, which can be carried out by a civil engineer. They will assess the impact of a major rain event and the impact this has on your property.

Typically they are looking for the expected water level and to ensure any new building construction would be sufficiently clear of this level. If your site has an overland flowpath (which is the watercource created in heavy rain), you will not be able to change the path of this on the entry or exit points of your boundary.

5. Existing Publicly Owned Assets On Site – Manholes etc

Any publicly owned manholes, cesspits or chambers on your property can not be built over. There needs to be a minimum 1m clearance away from any of these assets. Furthermore, you need to be 5m vertically clear of it. Depending on the asset and the network it is connected to, in some instances it is possible to have these relocated but this would be at your cost and there’s no guarantee that they would support this.

6. Sloping Sites / Excavations / Cuts / Retaining / Retaining Walls

Depending on the complexity of the site itself, an element of excavation, cut and filling may well be required and potentially the need for retaining walls. Council are very keen to understand the impact this might have on the site and the surrounding properties. They will insist that the neighbouring properties (particularly roads etc) are not adversely affected by any future development taking place.

They will want to see a construction methodology and sediment control plan to ensure that the necessary thinking and design has been considered. Getting the levels to ‘work’ can be a complex modelling process if the site is steep and getting access and house levels to comply with council requirements. Gone are the days when steep driveways, single access with reverse manoeuvring are simple to get through consenting phase.

So there you have it! These are the top issues we encounter when assessing sites and it pays to have a good civil engineer on board to help work through these issues.

If you find any of these issues a challenge on your particular opportunity, you’re not alone and they can be worked through with good design. But its always preferable to know about these issues before you are fully committed to a development as any one of these can significantly impact the profitability of your project.

Graeme Fan