Site coverage and hard surface: residential limits, stormwater triggers

TL;DR

Most suburban residential lots operate under two separate area controls: site coverage (roofed footprint as a percentage of site area, typically 50-60% maximum) and hard surface or impervious area (everything that sheds water, typically 60-80% maximum). They are not the same number and they are not the same control. The hard surface limit is the one that quietly bites builders late in a DA when the pool deck pushes you over the threshold and council comes back requiring an on-site detention (OSD) tank you haven’t budgeted for. Identify both controls on day one. Check your council’s DCP before you commit to a slab size.

What this article is for

Site coverage and hard surface controls are among the most commonly misunderstood planning limits on a residential lot. Many builders treat them as interchangeable. They are not. A dwelling can sit inside its site coverage limit and still breach its hard surface limit because of the driveway, pool surrounds, and paved entertaining area that were added without running the numbers.

This article explains:

How the two controls are defined and calculated.
What typically counts in each (and what doesn’t).
How hard surface thresholds interact with OSD requirements.
The permeable paving credit available in some jurisdictions.
A worked example on a 500m² lot.
How the controls vary across NSW, VIC, QLD, WA, and SA.
The builder gotchas that generate late-DA surprises.

The two definitions

These are distinct controls. Both must be satisfied independently.

Control	Definition	Typical maximum
Site coverage	Area of the site covered by roofed structures (dwelling, garage, carport, verandah, sheds) divided by site area	50-60%
Hard surface (also: impervious area, impervious surface, non-permeable area)	Area of the site covered by any surface that sheds water (site coverage + driveways + paths + paving + pool surrounds + decks) divided by site area	60-80%

What counts in site coverage

Dwelling footprint at ground level (including any ground-floor projection under an upper storey)
Roofed garage or carport (even if the sides are open)
Roofed verandah, covered outdoor entertaining area
Garden sheds and any other roofed outbuilding
Upper storeys that overhang the ground-floor footprint

What does NOT count in site coverage

Open-sided pergola with a shade sail or battens but no sheet roof
Unroofed deck or patio
Driveway, paths, paving
Eaves (in most jurisdictions, or up to a set width)
Swimming pool water surface
Underground basement (if fully below finished ground level)

These exclusions are the source of most confusion. A flat-roof steel carport with no walls counts. A timber pergola with a poly-carbonate sheet roof counts. A timber pergola with a shadecloth sail does not, in most states. Always check the definition in the applicable DCP or code rather than assuming.

What counts in hard surface (impervious area)

Everything in site coverage, plus:

Driveway (concrete, asphalt, pavers laid on mortar)
Paths and footpaths within the lot
Paved entertaining areas
Pool coping and surrounds
Concrete or paved pool decks
Tennis courts

Standard timber or composite decks on stumps are treated differently by jurisdiction. Some councils treat them as permeable (water drains through the gaps), others treat them as impervious. Check your DCP.

The stormwater detention trigger

When hard surface exceeds the council’s threshold, the additional runoff has to go somewhere. Council’s answer is usually an OSD system: an underground tank or in-ground retention area that captures the post-development peak flow and releases it slowly into the stormwater network.

Typical trigger: hard surface exceeds 60-70% of the lot, or increases impervious area by more than 100m² compared to pre-development (some councils use 40-60m² for additions). The trigger varies by council and by catchment. Some catchments have stricter controls because they are already over-capacity.

The OSD requirement shows up as a condition on your DA. If you did not budget for it, you are now looking at an underground tank (typically 5,000 to 25,000 litres for a suburban lot, depending on lot size and impervious coverage), a stormwater engineer’s design, and installation cost that can run to several thousand dollars. OSD is not optional once triggered. The building certifier will not issue an Occupation Certificate without evidence the system is installed and compliant.

Worked example: 500m² lot

Lot area: 500m² Site coverage limit: 50% (from council DCP) Hard surface limit: 70%

Element	Area (m²)
Dwelling footprint	180
Roofed garage	36
Roofed verandah	20
Site coverage total	236 (47.2% of 500m²)
Driveway (concrete)	42
Paved patio (unroofed)	25
Pool surround/coping	22
Paths	10
Hard surface total	335 (67% of 500m²)

This example sits inside both controls. But add a pool deck of 30m² and the hard surface hits 365m², which is 73% of the lot, breaching the 70% limit and triggering OSD.

The site coverage figure never moved. That is the point. Site coverage alone does not tell you whether you have a stormwater problem.

Permeable paving credit

Some councils credit permeable or porous paving at a reduced impervious rate for OSD calculation purposes, typically treating permeable paving as 50% impervious rather than 100%. This lets you add a driveway or entertaining area in permeable pavers and count it at half its area when calculating whether you exceed the OSD trigger.

The credit is not universal. It exists in some NSW councils and is emerging in other states as WSUD (Water Sensitive Urban Design) policy matures. To use it:

The product must be genuinely permeable, rated and installed to allow water infiltration to substrate. Poorly specified or clogged permeable paving does not qualify.
Your council’s DCP or stormwater engineering guideline must explicitly recognise the credit. Don’t assume it applies.
A hydraulic engineer’s report may still be required to confirm the substitution is valid for your specific catchment.

Even where the credit applies, it usually only reduces the OSD volume requirement rather than eliminating it entirely. Check with a civil or hydraulic engineer before specifying permeable paving as the sole OSD strategy.

State variance

The two controls exist in every Australian residential planning regime, but the percentages, definitions, and framing differ.

State	Site coverage control	Typical maximum	Hard surface / open space control	Notes
NSW	DCP-level, varies by council	50-60% (council-set)	DCP-level, varies by council; OSD typically triggered at >60-70% impervious or >100m² increase	No state standard; entirely council-by-council. Check your specific DCP chapter.
VIC	ResCode Standard A5 (single dwellings) and B8 (two or more dwellings), VPP Clauses 54.03/55.03	60% default (A5); 50% where lot exceeds 500m² under some interpretations; council schedule can reduce	ResCode addresses site coverage separately from permeability. “Permeability” standard requires a minimum permeable area (unroofed, unpaved). No universal hard surface maximum as a percentage; OSD via engineering overlay	Zone schedule can override the 60% ResCode default downward. Always check the zone schedule.
QLD	Planning scheme code, varies by LGA. QDC MP 1.1 (lots <450m²) and MP 1.2 (lots >=450m²) set siting rules	50-60% typical, scheme-code specific	Planning scheme codes set open space or permeability requirements. OSD via hydraulics report required on larger or sensitive lots.	Brisbane, Gold Coast, Sunshine Coast each have their own scheme codes with different numbers.
WA	R-Codes (SPP 7.3 Vol 1) frame the control as minimum open space, not maximum site coverage. Inverse of eastern states framing	R20: min 50% open space; R30: min 45% open space (effectively 50% and 55% maximum coverage respectively)	Open space = what is not covered. Driveways, parking, and roofed structures excluded from open space. Hydraulic drainage rules apply separately via council engineering standards	WA’s “open space” is the inverse metric: minimum proportion of lot that must be unbuilt. The effect is the same as a site coverage maximum but the DTS table reads as “minimum open space %“
SA	Planning and Design Code, zone-specific	Typically 60% in General Neighbourhood, Suburban Neighbourhood zones	Combination of site coverage, setbacks, and open space provisions in the Code. OSD via council stormwater requirements.	SA collapsed all 72 council Development Plans into the single P&D Code in 2021. Controls are now state-wide by zone, but hydraulic engineering requirements still vary by local stormwater catchment.

What can go wrong

Pool decks that quietly push you over. A pool is often designed as a late addition or priced as a variation. Add 20-30m² of pool coping and surrounds to a site that was already sitting at 65% hard surface and you have a breach plus an OSD trigger. The place to catch this is at design stage, not after the DA is lodged.

The surprise OSD condition. DA lodged, months pass, then council issues a condition: “prior to the issue of a Construction Certificate, the applicant shall provide a stormwater management plan incorporating an OSD system designed by a suitably qualified hydraulic engineer.” If OSD wasn’t in the preliminary estimate, the client’s budget takes a hit and the programme slips while you chase the hydraulic engineer. The fix: run the hard surface calculation at concept stage and flag OSD risk to the client before DA lodgement.

Council-by-council variance in what “hard surface” includes. Decks, permeable paving, compacted gravel, and artificial turf are all treated differently across councils and states. Do not assume what applied on the last job applies on this one. Read the DCP definition and, if unclear, get a pre-DA response in writing.

LEP vs DCP. In NSW the site coverage percentage is usually in the DCP, not the LEP. Some councils set a maximum in the LEP and allow the DCP to tighten it further. Read both documents. The more restrictive number applies.

Existing paving you inherit. On a knock-down-rebuild, the existing driveway and paths count toward the post-development hard surface total if you keep them. Do not assume the existing site is compliant, especially on older lots where historical paving was done without a DA.

DCPs: how to read them for a residential project explains how to navigate the specific chapter of your council DCP where the site coverage and hard surface numbers live.
NSW planning scheme structure and VIC planning scheme structure explain where the relevant instruments sit in the planning hierarchy for each state.
Landscaped area and deep soil requirements sit alongside site coverage and hard surface controls in most DCPs: see landscaped area and deep soil for how the open/soft area controls interact.
Floor space ratio is the third major site-level bulk control alongside site coverage. All three must be satisfied simultaneously.

References

Victoria Planning Provisions, Clauses 54.03-1 (Standard A5) and 55.03-3 (Standard B8), via planning.vic.gov.au (verified 2026-05-23).
SQM Architects, “ResCode Site Coverage Limits and Calculations”, via sqmarchitects.com.au (verified 2026-05-23).
State Planning Policy 7.3, Residential Design Codes Volume 1 (WA), via wa.gov.au (verified 2026-05-23).
Wollongong City Council, “On-site stormwater detention (OSD)”, via wollongong.nsw.gov.au (verified 2026-05-23).
Plans in Motion, “What is the difference between Garden Area, Site Coverage and Permeability?”, via plansinmotion.com.au (verified 2026-05-23).
Blacktown City Council, “On-site Stormwater Detention” fact sheet, via blacktown.nsw.gov.au (verified 2026-05-23).