Levels and grading plan: falls, steps and cut-and-fill balance

Where every finished surface sits relative to your datum, which way each falls, and whether the earth you cut out matches the earth you need to fill. Moving sand you did not need to move is the most common waste in a build.

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The layout plan says where things go. The levels plan says how high they are, and it is the drawing that decides whether the garden works or quietly wrecks the house.

Perth makes this easy to get wrong. The ground is sand and water disappears into it, so for a while levels seem not to matter. Then you compact a base, lay 60 square metres of paving, and you have built a shallow dish with a fall you never chose. The first serious winter front finds where that dish drains to. If the answer is “at the house” or “at the neighbour”, that is a repair bill and possibly a legal problem, not a puddle.

Renovating makes it harder, not easier. On bare sand you pick your levels. On an established block you inherit them: a slab poured in 1998, a crossover the council built, a fence line where the neighbour’s soil sits 200 mm higher than yours. Most of a grading plan is not a choice. It is arithmetic between fixed points.

What a professional does at this stage

First, list the levels that cannot move. House slab and door thresholds. Alfresco and garage floors. The crossover at the property boundary, which is set by the council’s crossover specification, not by you. Top of kerb. The invert of any existing soakwell or pit. Soil level at each boundary. And the ground level around any tree that is staying, because sand piled over a root plate kills the tree slowly enough that nobody connects the two events. Each of those gets a level relative to your site datum before a single new level is proposed.

Then work outwards until the numbers meet. Falls are set to the minimum that drains reliably, not the maximum the site allows, because every extra millimetre of fall is extra cut or fill at the far end. Where two fixed points cannot be reconciled by falls alone you get a step or a wall — decided on the drawing, not on site with a bobcat idling.

The amateur version is to level by eye and deal with drainage afterwards. Afterwards is when it costs five figures.

If you have not set a site datum, do levels, falls and datum first. Everything below assumes each level is an offset from one fixed reference point.

Falls: the numbers to design to

Fall is a ratio or millimetres per metre — the same thing. 1:100 is 10 mm/m, 1:50 is 20 mm/m.

Surface	Design fall	Note
Ground within 1 m of the house	50 mm over the first metre (25 mm only in low rainfall areas with an impermeable surface)	Clause 3.3.3(a), ABCB Housing Provisions. Not negotiable
Paving, concrete, liquid limestone	1:100 minimum, 1:80 preferred	1:100 is the working trade minimum; textured or large-format units need more, because laying tolerance eats the fall
Lawn that must shed water	1:100 minimum, 1:50 where it takes runoff	On deep sand lawn water goes down, not across — but not over a builder’s compacted pad
Path used daily	crossfall no more than about 1:40	Beyond that it feels wrong underfoot and drags a wheeled bin sideways
Anything that must stay dry	fall to a defined point, not “away”	A grated drain, a spoon drain, a bed with real capacity

Three rules go with that table.

One fall direction per surface. A terrace falling two ways has a ridge down the middle you did not draw and cannot see until it rains.

A surface with no stated fall has no fall. Write the arrow and the ratio on every one. Paving laid “roughly level” ends up a birdbath.

Draw the build-up, not just the finished level. A paved terrace is typically 40 to 50 mm of paver, 25 to 30 mm of bedding sand and at least 100 mm of compacted crushed limestone — about 175 mm. Your plan works to finished levels; your excavator works to subgrade, 175 mm lower. Forgetting that is the most common reason a cut-and-fill number is wrong by a truckload. Carry it into base preparation.

Where the water is allowed to go

Not at the house. A slab-on-ground must sit at least 150 mm above finished ground level, or 100 mm on sandy well-drained ground, or 50 mm above paving that slopes away. Raising a bed or a terrace until it swallows that clearance bridges the damp-proof course and covers the inspection zone termite management depends on. If your existing paving already sits hard against the brickwork, that is a defect to fix here, not a level to match.

Not at a boundary. Performance Requirement H2P1 requires surface water collected or concentrated by a building or sitework to be disposed of without likelihood of damage or nuisance to any other property. Perth councils put it more bluntly: the City of Joondalup requires all stormwater falling within the lot boundaries to be contained on site, citing the common law and Local Government Act 1995 obligation not to let water run from your land onto anyone else’s. Grading a terrace so it sheds next door is not a neighbourly disagreement. It is a liability you built on purpose.

Every arrow must terminate somewhere legal — a soakwell, a soakage bed, a swale, a planted area with real capacity, or an approved connection. “Towards the fence” is not a destination. Size the receiving device in the drainage plan, and check what water on site said about your watertable before planning to soak anything away in winter.

Steps

Riser consistency is a safety issue, not an aesthetic one. People climb by feel after the second tread, and a riser 20 mm out of pattern is a fall.

Design to the Housing Provisions numbers: riser 115 to 190 mm, going 240 to 355 mm, 2R+G between 550 and 700 mm, adjacent risers differing by no more than 5 mm and the largest and smallest in a flight by no more than 10 mm. A flight must have at least two risers — the code’s way of saying the single garden step everyone builds is a trip hazard.

Set them out by arithmetic:

Total rise = upper finished level − lower finished level. Say 640 mm.
Divide by a target riser: 640 ÷ 150 = 4.27, so use 4 risers.
Actual riser = 640 ÷ 4 = 160 mm, every one. Not three at 165 and a last one at 145 because that is what was left.
Check 2R+G. With an outdoor going of 350 mm: (2 × 160) + 350 = 670 mm, inside range.

Garden steps feel best at the low-riser, deep-going end. If the rise will not divide neatly, shift the top or bottom landing by 20 or 30 mm and absorb it in the adjoining falls. That is what a grading plan is for.

Cut and fill

The aim is balance: the sand you dig out roughly equals the sand you need to build up, so nothing leaves site and nothing arrives. Cartage in both directions is pure waste.

Use the grid method. Overlay a 2 m or 3 m grid on the plan, and at each intersection write the existing level and the proposed finished level and subtract. Positive is cut, negative is fill. Average across each square, multiply by its area, add them up.

Worked example: a terrace 6 m by 4 m, ground falling 300 mm along its length, finished level set at the midpoint. Over the upper 3 m you cut, averaging 75 mm — 3 × 4 × 0.075 = 0.9 m³. Over the lower 3 m you fill the same 0.9 m³. Balanced. Then deduct the 175 mm pavement build-up across all 24 m², which is another 4.2 m³ of spoil with nowhere to go.

Two adjustments before booking anything. Sand bulks — a cubic metre in the ground is more than a cubic metre in the bin, so ask your carter what factor they use. Fill compacts — placed in layers of not more than 150 mm and mechanically compacted, as clause 3.2.1 requires, delivered fill occupies less than the volume you bought.

Then check you have not accidentally designed a retaining wall. Un-retained cut is limited to 2 m deep and fill to 2 m high, both inside your own boundary, and the maximum un-retained batter in sand is 1:2 — one vertical to two horizontal. A 600 mm level change therefore eats 1.2 m of horizontal space as a slope, which on a typical Perth lot is where a wall becomes cheaper than the batter. A wall brings approval and engineering obligations: check retaining walls approval and the R-Codes and your council before committing.

Safety, plainly

Excavation is the dangerous part of this phase, and the grading plan is where the depth gets decided — on paper, while it is still free to change.

Do not cut up to a boundary. Excavating beside a dividing fence or under a neighbour’s footing can undermine both. Joondalup’s soakwell rule of thumb — set back at least the depth of the excavation from buildings and boundaries — is a sound test for any hole in sand.
Sand collapses without warning, dry or saturated. Never enter an unsupported excavation deeper than about a metre, and never alone.
Know what is buried before setting a cut level. A 400 mm cut across an old service run finds the service: locating services.
Cutting pavers, limestone or concrete to make falls work releases respirable crystalline silica. Wet cutting and respiratory protection, every time.
Check what you will hit. If your soil test found limestone at 400 mm, a 500 mm cut is a rock-breaker hire, not a shovel.

What happens to this next

Every finished level on this plan feeds the sections in hardscape details — the next lesson, which takes each surface and draws what sits under it, how the edge is restrained and how the level change is held. The cut and fill volumes go into quantity take-offs as cubic metres of excavation, cartage and imported fill, and the levels themselves become pegs and string lines in earthworks and setting out.

Do this on your own block

Field journal entry

Levels and grading plan

Mark the finished level of every surface, the fall direction and gradient of each, all step locations and riser heights, and calculate your cut-and-fill volumes. Confirm every surface drains somewhere legal.

Checklist

Every paved surface has a stated fall and direction
No water is directed at the house or a boundary
Steps have consistent riser heights
Cut and fill volumes are calculated and roughly balanced

Where to go deeper

Every link below was fetched and checked before it shipped. Nothing here is a guess.

Freegovernment20 minAustralian
ABCB Housing Provisions Part 3.3 — Drainage
Australian Building Codes Board
Why this oneThe two numbers that govern every level you set near the house, free and from the source. Clause 3.3.3(a) requires the external finished surface around a slab to fall away from the building by at least 50 mm over the first 1 m (25 mm only in low rainfall areas with an impermeable surface), and 3.3.3(b) sets the minimum height of the slab above what you build against it — 150 mm in the general case, 100 mm on sandy well-drained ground, and only 50 mm above paving or concrete that slopes away. Read 3.3.5 as well: the position and manner of stormwater discharge must satisfy the appropriate authority, which in Perth is your local government.
Change this for Perth
Western Australia adopted NCC 2025 on 1 May 2026 with a 12-month transition, so work permitted during the transition may be assessed against either NCC 2022 or NCC 2025. The 3.3.3 figures quoted here are identical in both editions, so the numbers do not change; the clause numbering does not either.
Link checked 2 Aug 2026
Freegovernment15 minAustralian
ABCB Housing Provisions Part 3.2 — Earthworks
Australian Building Codes Board
Why this oneThis is the clause that tells you when your grading plan has quietly become a retaining wall project. Un-retained cuts must stay within the allotment and go no deeper than 2 m below natural ground level, un-retained fill no more than 2 m above it, and fill must be placed and mechanically compacted in layers not more than 150 mm. Table 3.2.1 gives the maximum un-retained batter slope by soil type — for sand it is 1:2, one vertical to two horizontal — and Note 2 states that a retaining wall must be installed where the embankment is steeper than that.
Change this for Perth
The 1:2 sand figure is the batter you can hold without a wall, which on a Perth block means a 600 mm level change eats 1.2 m of horizontal space. On a typical 400 to 500 square metre lot that is usually the moment terracing with a wall becomes cheaper than battering. Your council may also require a building permit or engineering for the wall itself — see the approvals phase.
Link checked 2 Aug 2026
Freegovernment20 minAustralian
ABCB Housing Provisions Part 11.2 — Stairway and ramp construction
Australian Building Codes Board
Why this oneThe dimensional rules for steps, which is where amateur landscape drawings fail most often. Table 11.2.2a sets risers between 115 mm and 190 mm, goings between 240 mm and 355 mm, and the slope relationship 2R+G between 550 mm and 700 mm. Clause 11.2.2 adds the consistency rules that matter outdoors: adjacent risers or goings may differ by no more than 5 mm, the largest and smallest in a flight by no more than 10 mm, and a flight must have not more than 18 and not less than 2 risers.
Change this for Perth
These provisions bind stairways that form part of a building. A freestanding garden step in the middle of a lawn is not automatically caught, but the dimensions are the safe-movement benchmark a court, an insurer and a building surveyor will all reach for. Design to them anyway. Where your steps are part of the path to the dwelling entrance, they are caught.
Link checked 2 Aug 2026
Freegovernment15 minAustralian
NCC 2025 Volume Two, Part H2 — Damp and weatherproofing
Australian Building Codes Board
Why this onePerformance Requirement H2P1 is the legal sentence behind the whole lesson: surface water from a storm with a 5% annual exceedance probability, collected or concentrated by a building or sitework, must be disposed of in a way that avoids the likelihood of damage or nuisance to any other property, and water from a 1% AEP storm must not enter the building. Note the words 'or sitework' — your paving, your terrace and your regraded lawn are sitework. H2D2 then points at AS/NZS 3500.3 or Part 3.3 of the Housing Provisions as the compliant path.
Link checked 2 Aug 2026
Freegovernment10 minPerth / WA
On Site Drainage Requirements (FACT105)
City of Joondalup
Why this oneA two-page Perth council fact sheet that states the rule plainly: the City requires all stormwater falling within the lot boundaries to be contained on site, through soakwells, drainage cells, sumps or other approved methods, and property owners have a statutory obligation under common law precedents and the Local Government Act 1995 to prevent water running from their land onto any other land. It gives the small-residential design criterion as the 20 year, 5 minute storm event, requires an above-ground overflow path so an overloaded system does not flood the house, and sets soakwell setbacks from buildings and boundaries at least equal to the depth of the soakwell so the excavation does not undermine fences, retaining walls or footings.
Change this for Perth
Joondalup's own sheet, last updated July 2016, and the containment rule is common across Perth councils rather than unique to Joondalup. The design storm, the soakwell sizing chart and the setbacks vary between local governments — confirm the current figures with yours before you size anything.
Link checked 2 Aug 2026
Freegovernment1 h+ for the relevant chaptersPerth / WA
Stormwater Management Manual for Western Australia
Department of Water and Environmental Regulation
Why this oneThe state's own manual, free by chapter, and the reference your council's engineers are working from. Chapter 9 on structural controls is the useful one for a residential block — infiltration basins, soakwells, swales and bioretention, with the design logic for each. It is the document to read if your grading plan needs to put water somewhere other than a soakwell, for example into a planted soakage bed or a swale along a fence line.
Change this for Perth
Written for catchment and subdivision scale, not for one garden, and chapters 3 and 4 have been superseded by other planning documents. Take the principles and the device design from Chapter 9 and ignore the planning-process material.
Link checked 2 Aug 2026
Freestandard45 minAustralian
ABCB Livable Housing Design Standard
Australian Building Codes Board
Why this oneFree PDF download, and the document NCC Volume Two Part H8 calls up for new Class 1a dwellings. It contains the technical provisions for a step-free path of travel to the dwelling entrance and a step-free entrance door, which is exactly the constraint that decides whether your front path can have steps at all. If anyone in the household may need level access now or later, set your finished levels to these provisions rather than discovering them after the paving is down.
Change this for Perth
It is called up by the NCC for new dwellings. On a renovation to an existing house it is not being enforced against your garden, but it is the only free, national, dimensioned reference for step-free access and it costs nothing to design to.
Link checked 2 Aug 2026
Freegovernment10 minPerth / WA
Crossovers
City of Stirling
Why this oneA worked example of the constraint most people forget: the crossover between your boundary and the kerb belongs to the council, not to you. Stirling requires prior approval for all crossover works, publishes separate specifications for residential concrete, brick-paved and non-residential crossovers, sets minimum setbacks from street trees of 1 to 4 metres depending on trunk size, and offers a contribution towards a first crossover built to its requirements. Your driveway level at the boundary is fixed by that specification, so it is a fixed point on your grading plan.
Change this for Perth
City of Stirling only. Every Perth local government has its own crossover specification, setbacks and subsidy — read your own council's before you set a driveway level.
Link checked 2 Aug 2026

The rules, with sources

WA regulation changes. Each point below names its primary source and the date it was last checked — always confirm with your own council before you build.

Surface water from a storm with a 5% annual exceedance probability that is collected or concentrated by a building or sitework must be disposed of in a way that avoids the likelihood of damage or nuisance to any other property. Surface water from a 1% annual exceedance probability storm must not enter the building.
NCC 2025 Volume Two, Performance Requirement H2P1, Australian Building Codes Board ↗ · checked 2 Aug 2026
The external finished surface surrounding a slab must be drained to move surface water away from the building and graded to give a slope of not less than 50 mm over the first 1 m from the building, or 25 mm over the first 1 m in low rainfall intensity areas where the surface is impermeable or is an accessible path.
ABCB Housing Provisions, clause 3.3.3(a) ↗ · checked 2 Aug 2026
A slab-on-ground must be not less than 150 mm above the finished ground level, reduced to 100 mm in low rainfall intensity areas or in sandy, well-drained areas, and 50 mm above impermeable (paved or concrete) areas that slope away from the building.
ABCB Housing Provisions, clause 3.3.3(b) ↗ · checked 2 Aug 2026
Un-retained site cuts must be within the allotment and not deeper than 2 m from natural ground level; un-retained fill must be placed within the allotment, mechanically compacted in layers not more than 150 mm, and not more than 2 m in height from natural ground level. The maximum un-retained embankment slope in sand is 1:2, vertical to horizontal, for both site cut and compacted fill, and a retaining wall must be installed where the slope is steeper.
ABCB Housing Provisions, clause 3.2.1 and Table 3.2.1 ↗ · checked 2 Aug 2026
Stair risers must be not less than 115 mm and not more than 190 mm, goings not less than 240 mm and not more than 355 mm, and 2R+G must be between 550 mm and 700 mm. Adjacent risers or goings may differ by not more than 5 mm, the largest and smallest riser or going in a flight by not more than 10 mm, and a flight must contain not more than 18 and not less than 2 risers.
ABCB Housing Provisions, clause 11.2.2 and Table 11.2.2a ↗ · checked 2 Aug 2026
The City of Joondalup requires all stormwater falling within the lot boundaries to be contained on site, and states that property owners have a statutory obligation under common law precedents and the Local Government Act 1995 to prevent water from running from their land onto any other land. For small residential development the design criterion used is the 20 year, 5 minute storm event.
City of Joondalup, On Site Drainage Requirements (FACT105) ↗ · checked 2 Aug 2026
Western Australia adopted NCC 2025 on 1 May 2026, with a 12-month transition period during which either NCC 2022 or NCC 2025 may apply.
Australian Building Codes Board, NCC 2025 state and territory adoption information ↗ · checked 2 Aug 2026