Coastal Hazard and Flood Overlays on the Sunshine Coast

If your block sits inside a coastal hazard or flood overlay, you can usually still build on it. What the overlay changes is how you build: your finished floor level, how far back from the beach your walls and pool can sit, what materials you can use below the flood line, and whether a private certifier can sign the job off or it goes to council as a development application first. On the Sunshine Coast those layers sit in the Sunshine Coast Planning Scheme 2014; in Noosa Shire, The Noosa Plan 2020. Underneath both are State lines — the erosion prone area and the coastal building line — that councils map but do not draw.

Who draws the lines, and who applies them

The erosion prone area is a State declaration. Under section 70(1) of the Coastal Protection and Management Act 1995, the chief executive may declare an area within the coastal zone to be an erosion prone area “if satisfied the area may be subject to erosion or tidal inundation”. Coastal building lines are fixed under section 66 of the same Act, which provides that a regulation or a notice declaring a coastal management district “may fix a coastal building line for a coastal management district” for assessing assessable building work. Councils then map those State lines and add their own modelling on top: Sunshine Coast Council states that “Part 8 contains the overlay codes for 13 overlays mapped in schedule 2 (mapping)”, among them coastal protection (8.2.5), flood hazard (8.2.7), acid sulfate soils (8.2.1) and landslide hazard and steep land (8.2.10).

Overlay-by-overlay implications table

The coastal protection overlay in practice

The code’s stated purpose is to protect people and property from coastal hazards, to protect coastal landforms and vegetation and allow for natural fluctuations of the coast “to the greatest extent practicable”, to take account of the predicted effects of climate change including sea level rise, and to maintain or enhance public access to the coast. Outside the erosion prone area you design normally. Inside it, the first acceptable outcome is not to be there.

Where redevelopment of an existing urban site is unavoidable, the code contemplates a layout that minimises the footprint within the erosion prone area, locates permanent structures as far landward as possible, and designs and constructs buildings to withstand coastal erosion impacts. What the code treats as straightforwardly acceptable inside the area is much narrower: temporary, relocatable or expendable structures, which its note describes as including portable or demountable towers, equipment sheds, lookouts, shelter sheds, decks and pergolas that are unattached, non-permanent, and “capable of being easily and quickly removed when threatened by erosion”.

The trap for renovators is the definition of a permanent structure: the code’s note is explicit that swimming pools and retaining walls count. A pool pushed seaward of the line is the difference between accepted development and a development application. Settle it before you commit to a scheme — see renovate or knock down and rebuild.

Flood hazard on the Sunshine Coast: two maps, not one

Sunshine Coast Council runs two flood layers. The first is the planning scheme’s flood hazard overlay, used for development assessment. The second is a flood hazard area designated for building regulation purposes, which council resolved on 21 September 2023 (resolution OM23/99) under the Building Act 1975 and Building Regulation 2021. Council explains that the building map includes “additional buffer areas that are relevant to building works, and account for overland flow paths, drainage and freeboard”. So a property can be clear on one map and caught on the other, and council warns that “the absence of flood mapping does not imply that a property is not subject to localised stormwater flooding or drainage issues”.

Design around one detail early. The scheme’s acceptable outcome for materials is that building materials and surface treatments used below the defined flood event or defined storm tide event are resilient to water damage and do not include wall cavities that may be susceptible to the intrusion of water and sediment. That rules out ordinary stud-and-plasterboard at the lower level, and it must be settled before the frame is ordered — the same discipline we apply on new home builds across the Sunshine Coast.

Noosa runs a different system

Noosa treats the two hazards very differently from each other. Council’s fact sheet states that all development proposed within the Coastal Protection and Scenic Amenity Overlay is assessable development, to be assessed against both the overlay code and the State Planning Policy coastal hazards benchmarks — that state interest is not yet fully integrated into The Noosa Plan 2020, so under the Planning Regulation 2017 the SPP benchmarks apply. A Coastal Hazard Assessment prepared by a suitably qualified person must come with the application, and council engages a third party consultant to peer review it at the cost to the applicant, per its fees and charges schedule. Council is completing a Coastal Hazards Adaptation Plan, and says future amendments to The Noosa Plan 2020 will follow.

At the flood edge the pathway is looser for a house. Council’s mapping of the erosion prone area accounts for long term erosion, short term erosion from a 1% AEP wave height and 1% AEP storm tide level, slumping of the eroded dune, recession of the beach under sea level rise and a 40% factor of safety, across four planning periods: present day, 2040, 2070 and 2100. Council calls that mapping “indicative only” and says it should not be relied on for detailed design decisions at the individual lot scale, which is why the site-specific assessment exists. On flooding, a dwelling house is expressly excluded from assessment against the Flood Hazard Overlay Code, with the minimum floor level requirement sitting in the Low Density Housing Code instead. Our work at Redwood Avenue, Marcus Beach sits in Noosa Shire, under these rules.

Storm tide is not flood, and MP 3.5 does not cover it

Queensland Development Code MP 3.5 applies to building work carried out wholly or partly within a flood hazard area where a defined flood level is declared by a local government, but it expressly does not apply to a building located, or proposed to be located, on a lot subject to storm surge. Storm tide is handled through the planning scheme, not that part of the building code, and that catches people out.

MP 3.5 is also narrower than most owners assume. It catches construction of a new class 1 building and “additions to a class 1 building where the additions constitute 50% or more of the floor area of the existing building”. It does not catch alterations that are not additions to floor area, repairs to an existing building, building work directly related to raising an existing building, or adding an extra storey above an existing part. Its acceptable solution A1(a) applies only on a lot, or part of a lot, in an area with a maximum flow velocity not greater than 1.5 metres per second, or in an inactive flow or backwater area. Outside that, you are into an alternative solution and a competent person.

Sunshine Coast Council endorsed an updated storm tide study on 24 October 2024, with planning levels based on a planning horizon of the year 2100. Council states that in locations adjacent to small coastal creeks, an additional 400mm allowance is to be added to new floor levels to provide extra protection from waves. That 400mm can decide slab-on-ground versus a suspended floor.

What overlays do to a budget and a program

No honest builder quotes a flat overlay surcharge, because the cost driver is not the overlay, it is what the overlay forces into the design. The recurring drivers are:

• Assessment path. Work that would have been accepted development becomes a development application, adding a council stage before building approval — see building approvals on the Sunshine Coast and Noosa.
• Specialist reports. Coastal hazard assessments, flood searches, geotechnical work and acid sulfate soils investigations, plus the peer review in Noosa.
• Ground conditions. The acid sulfate soils overlay maps Area 1 as land at or below 5 metres AHD, so low coastal land caught by flood mapping is often caught by that overlay too. Where disturbance is unavoidable the code’s acceptable outcome is an investigation conforming to the Queensland sampling guidelines, with soil analysis to the laboratory methods guidelines or Australian Standard 4969, and acidity neutralised and managed.
• Structure and materials. Raised or suspended floors, deeper footings, framing that resists hydrostatic and hydrodynamic action, and water-resilient construction below the flood level.
• Earthworks limits. For an accepted dwelling house, the flood overlay’s acceptable outcome is that filling outside the plan area of all buildings and driveway areas does not exceed 50 square metres and does not result in net filling on the site, so you cannot simply raise the land out of trouble.

Headland and hillside blocks stack the landslide hazard and steep land overlay on top of this, covered in building on a sloping block in Queensland.

How to check a block before you commit

Order the searches before contract, not after. On the Sunshine Coast, start with council’s Development.i site report: council states that for simple situations where a property flood information search can be automated, the information relevant to MP 3.5 is provided there, tabulated under the flood hazard area for building regulation purposes map. For more complex situations the search cannot be automated and a manually created flood information search is required, which council describes as a paid service; fees apply to searches requested through its online services. Where the works are accepted development for a new dwelling, council notes the search is normally requested by your building certifier.

In Noosa, confirm the overlays on council’s interactive mapping and buy a flood search certificate, which returns a flood level for the property, the minimum building height new habitable rooms are required to build to, modelled flood levels, historical flood levels, and flood velocity where available. Then have a builder and designer read those numbers together, because a floor level and a coastal setback both eat into what you can build. Roebuck Concepts works out of Coolum Beach across the Sunshine Coast and Noosa Shire.