VHR involves the raising of eligible houses to protect them from flooding. Single storey weatherboard or timber houses constructed on piers are typically best suited for house raising. House raising works involve lifting the house using a combination of beams and jacks, after which piers are installed and raised to the new floor level. Houses constructed with a concrete slab-on-ground are not able to be raised. Commercial properties are not eligible for raising.

Houses are raised to the Flood Planning Level, which is defined as the peak flood level during the 1% Annual Exceedance Probability (AEP) flood, or 1 in 100 years flood, plus a freeboard of 500mm. The area under the raised house is not to be used as a habitable living area, however this space can be used as a garage.

Examples of houses being raised are shown below:

The 2023 Floodplain Risk Management Plan identified several properties for further assessment and, if found to be appropriate, inclusion in a Voluntary House Raising Scheme.

Each house has been assessed against a range of eligibility criteria outlined by the NSW Government’s Floodplain Management Program. The criteria are outlined in the Guidelines for the Voluntary House Raising Scheme.

Eligible dwellings need to be:

• Located outside of High Flood Hazard areas (i.e., areas of high depth and flow velocity).
• Located outside of dedicated Floodway areas, which are required for conveying flows during a major flood.
• Constructed prior to 1986.

Several houses lie within high hazard and floodway areas during the Nepean River 1% AEP flood, which means often houses positioned lower in the floodplain are not eligible for house raising. Council may consider the investigation of alternative options to mitigate flood damages and risk for these properties, such as voluntary house purchase.

Approximately 20 dwellings located at the edge of the Nepean River floodplain meet the eligibility criteria for voluntary house raising. It was determined that the houses would need to be raised by between 0.7 and 2 metres.

A benefit-cost assessment has been completed for each house, considering the present value of the following over a 50-year life span of the dwelling:

• The reduction in flood damages (benefit) that is expected as a result of raising the house, accounting for the full range of potential flooding up to the 1% AEP flood and higher.
• The cost of the house raising works, which is based on cost rates per square metre according to building industry sources.

The assessment has shown that the house raising works are expected to have a Benefit-Cost Ratio (BCR) ranging between 0.3 and 0.5 for each property. The flood damages reduction benefit is not expected to outweigh the cost of the works. However, the works can still be worthwhile to manage flood risk and reduce flood damages.

The 20 properties will be recommended for inclusion in a Voluntary House Raising Scheme. Houses have been given a priority order according to the Benefit-Cost Ratio, which also typically reflects those houses currently under the most risk of flooding.

If included in the final Voluntary House Raising Scheme, the NSW Government would provide funding equivalent to two-thirds of the cost of house raising.

The property owner would be responsible for payment of one-third of the house raising cost. Funding from the NSW Government can only be used towards the cost of the house raising works. Any additional renovations or building works undertaken concurrently by the homeowner would need to be paid by the homeowner.

Landowners of dwellings identified for potential house raising were consulted in April 2024. A number of items were raised by the landowners that attended the consultation session, which are addressed as follows.

If there is support to make application, Council will need to apply to access the VHR scheme pool of funding offered by the NSW Government. If the application is approved, access to the funding pool is given for a three-year period.

Council will administrate the scheme which then proceeds based on the priority list, landowners are offered but not obligated to participate. When a landowner confirms they wish to go ahead with house raising, Council confirms that funds are available and a Work Plan is entered into based on 3 house raising quotes, which are to be sourced by the property owner from local builders.

At any stage of the process prior to contracting the builder, the landowner can choose to proceed or opt-out of the scheme. If they choose to not proceed with the works, Council will look to offer the funding to the next property on the priority list.