Measuring up: a base plan without paying a surveyor

Every drawing in Phase 5 and Phase 6 sits on one sheet of paper: a scaled base plan of your block with everything permanent marked on it. Get that sheet wrong and every number downstream is wrong with it — paving area, turf area, metres of retaining, litres per hour, the quote you build from.

On a flat suburban block with a house on it you do not need a surveyor. You need a long tape, two hours and a method. What you do need from someone else is the boundary geometry, and in Western Australia that comes from Landgate, not from your fence.

What a professional does at this stage

Someone who measures up for a living does three things, and the order is the point.

They get the plan before they get out of the car. Lot dimensions, area, easements and parcel shape come off the deposited plan, diagram or scheme plan held by Landgate. A tape gives you a length; the plan gives you the legal length. When the two disagree, that disagreement is itself a finding.

They measure the house, not the garden. It is the only object on site with reliably straight lines and near-right angles, so it becomes the frame everything else hangs off. Beginners start at the back fence and work inwards, which is how error accumulates until the last corner is out by 300 mm.

They close the survey before leaving site. Every critical figure is checked against a second measurement taken a different way. That discipline is most of the difference between a base plan you can build from and a sketch.

Start with the title, not the tape

Order two things from Landgate. A copy of the Certificate of Title gives you the lot and plan number, the registered proprietor, and any easements, covenants or notifications over the land. A copy of the survey plan — the deposited plan, diagram or survey-strata scheme plan referenced on that title — gives you the boundary dimensions and lot area. Both are $33.90, no GST, and arrive as PDFs by email.

If your block is a survey-strata lot or a battleaxe, which a great deal of Perth infill is, the scheme plan also shows common property, the driveway easement and any restricted-use areas. Those constrain a design far more than people expect.

The fence is not the boundary

Perth dividing fences built between the 1960s and the 1990s were routinely set out by eye, or to a peg that has since been knocked, and limestone block boundary walls are thick, heavy and frequently sit 100–200 mm off line. If your taped boundary comes up short of the plan dimension, do not correct the plan — record both numbers and note which one you drew.

That discrepancy stops being trivia the moment you propose retaining, a pool or a structure near the line, and only a licensed surveyor can resolve it. See dividing fences and the R-Codes and your council.

Kit

A 30 m open-reel tape does the work — fibreglass is forgiving, steel is more accurate but kinks. Add an 8 m pocket tape for detail, a screwdriver to anchor the far end if you are alone, and a clipboard with A3 paper and a pencil. A laser meter earns its keep indoors and in shade, but in direct Perth summer sun the dot washes out well before the back fence. Sketch the block roughly first, filling the page, and never try to draw to scale on site.

The method

Running dimensions along the house

Pin the tape at one corner of the house and run it along the wall. Read a cumulative value at every feature you pass — window reveal, window reveal, door jamb, door jamb, downpipe, tap, meter box — and finish with the overall length as the last reading. Measuring each gap separately means every reading carries its own error and they all add up; running dimensions accumulate nothing, and the final overall checks everything before it for free.

Triangulation for everything else

Pick two fixed points on the house at least 4 m apart that you can identify again later — two external corners are ideal. Call them A and B. For every object you want to locate, measure the distance from A and the distance from B. Two lengths fix one point absolutely, because a triangle with three known sides has only one possible shape.

On the drawing, set a compass to each distance, swing an arc from A and an arc from B, and the object sits where they cross. Keep the triangles fat: if the arcs meet at a shallow angle the intersection smears over several centimetres and the fix is worthless.

Triangulate every boundary corner, every tree trunk, the shed corners, the gate posts, the bore head, the soakwell lids and the meter.

Offsets for curves

Lay the tape between two already-known points as a baseline, then measure at right angles from it to the curve every metre or two. Enough offsets and the curve draws itself — the right tool for a curved bed edge, a meandering path or the drip line of a big tree.

Closing checks

Four checks before you pack the tape away.

1. Both diagonals of the house rectangle. If they differ, the house is not square, which is normal. Draw it as measured, not as assumed.
2. Both diagonals of the block, against what the Landgate plan dimensions would produce.
3. Every running-dimension chain sums to its own overall. If it does not, one reading in that chain is wrong.
4. A third measurement from a third point on anything important. If the third arc misses, one of the three is bad and you are still on site to find out which.

The Perth things people forget to record

Item	Why it matters later
Bore head, pump and pressure tank	Position and access drive the whole irrigation layout — see irrigation water source
Reticulation solenoid boxes and controller	Existing valves and wiring may be reusable, which is real money
Soakwell lids and downpipe discharge points	Perth stormwater is generally retained on site; confirm the requirement with your council
Water meter, gas meter, NBN pit, power point of attachment, aircon condenser	Immovable, and some cannot be built over
Eave overhang, measured separately from the wall line	Drives shade and where roof water lands
Crossover, kerb and verge trees	The verge is council land, not yours
Existing limestone or block retaining, with heights	Height decides whether new work needs approval
Gate and door swings	Kills more paving layouts than anything else

Surface evidence only at this stage. Finding what is buried is locating services; the plants and structures themselves get judged in auditing an existing garden and tree assessment.

Drawing it up

Work at 1:100 unless the block is large. An A3 sheet at 1:100 covers roughly 42 by 29.7 metres, which fits most Perth blocks with room for notes; drop to 1:200 for anything bigger. Draw the house first from your running dimensions, then swing your arcs off it.

Put four things on the sheet: scale, north point, date, and the source of your boundary dimensions — in two months you will not remember whether you drew the fence or the plan. Then go back outside and check two diagonals off the finished drawing against the ground. Last chance to catch a transposed number.

When a feature survey is worth paying for

A licensed surveyor’s feature and contour survey gives you spot levels tied to Australian Height Datum, contours, tree positions and a CAD file a designer can draw straight onto. Perth firms quote fixed prices and turn quotes around in a couple of days — get two, and do not accept an hourly rate. Pay for one when:

• The block falls more than roughly a metre overall, or the design depends on accurate falls for drainage
• You are building retaining, a pool, or any structure close to a setback
• You suspect an encroachment, or your taped boundaries disagree with the Landgate plan by more than about 50 mm
• The lot is survey-strata or battleaxe with a shared driveway
• You are in the Hills — Kalamunda, Roleystone, Darlington, Mundaring — where eyeballing levels is hopeless

Boundary determination in particular is not work you can do yourself. Under the Licensed Surveyors Act 1909 only a registered surveyor with a current practising certificate may carry out cadastral surveying in WA, and Landgate does not do it for you.

The next lesson, levels, falls and datum, takes this base plan and adds the third dimension — where the block falls, by how much, and what that does to your drainage and your retaining. Everything you have just drawn becomes the sheet those levels get written onto.