Site Set Out & Foundations: A Practical Owner Builder Guide (Australia)
Getting the site set out and foundations right is one of the most important parts of any owner‑builder project. Everything that follows (floors, walls, roof, doors, windows) relies on your foundations being square, level, and in the correct position.
This guide is based on our real‑world experience setting out and building pier foundations for an owner‑built home in Australia.
We’re not builders, instead we learned by doing, made mistakes, and worked closely with engineers and inspectors. If you’re planning a DIY build, this article can hopefully help you avoid costly errors and approach your foundations with confidence.
Step 1: Understanding Site Set Out
Site set out transfers your approved plans from paper to the ground.
It involves:
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Marking the exact house location on the block
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Establishing square corners
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Setting correct dimensions for the house and decks
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Creating durable reference points for the entire build
If wrong, it can cause:
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Incorrect pier placement
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Setback breaches (potential fines)
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Later issues with framing, flooring, and roofing
Tip:
Never rush this stage. Spending a full day perfecting corners is time well spent.
Step 2: Start with Boundaries and One Perfect Corner
Safest approach:
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Run taut string lines along boundary pegs.
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Measure setbacks from plans to locate the first house corner.
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Secure it firmly (e.g., with a star picket).
Everything flows from this corner if it's off, subsequent measurements compound errors.
Extra Tip:
If pegs are missing or unclear, hire a licensed surveyor for re-pegging.
Step 3: Squaring the Building – The 3-4-5 Method
Perfect 90° corners are essential for accurate site set out and pier foundations in Australian owner-builder projects.
How it works:
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Mark 3 metres along one wall string line.
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Mark 4 metres along the adjacent wall string line.
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Measure the diagonal – it must be exactly 5 metres for a true right angle.
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If not, adjust the strings until it is.
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Repeat for all four corners.
For larger accuracy:
Scale up the ratio (e.g., 6m - 8m - 10m or 9m - 12m - 15m) to minimise measurement errors on bigger layouts.
Why it matters:
This Pythagoras-based technique guarantees right angles, critical for compliant foundations. A square set out ensures proper pier alignment, even load distribution, and avoids structural issues.
Tips:
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Use a high-quality steel tape measure (avoid fibreglass tapes, as they can stretch and compromise accuracy).
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Check both full building diagonals for overall squareness.
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Re-check after disturbances.
Step 4: Batter Boards & String Lines
Batter boards (also called profiles) are temporary stakes with horizontal timbers set 1-2m outside the building footprint. They support string lines for marking external walls, internal lines, and pier centres, creating a fixed reference system that withstands excavation.
Tips:
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Set boards at a consistent height (e.g., 100-200mm above ground) for easier levelling integration later.
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Use two parallel strings per wall to account for wall thickness or pier offsets.
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Label each board clearly (e.g., "North Wall Corner") to prevent mix-ups during multi-day work.
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Opt for treated timber or metal stakes for durability in wet conditions.
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Fix screws or nails at string intersections for easy removal and exact reinstallation during digging.
Caveats:
Wind or animals can loosen strings check tension daily. On reactive soils (common in Australia), boards may shift slightly; re-verify against boundaries if needed.
Step 5: Marking Pier Locations Accurately
Once strings are set, use a plumb bob suspended from intersections to mark exact centres on the ground. Spray paint oversized circles (e.g., 600mm for 450mm piers) and drive temporary stakes for visibility.
More Info:
This ensures piers align with bearers and joists, complying with engineering for load paths in pier-and-beam systems.
Tips:
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Use fluorescent spray for high visibility on dark soil.
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Double-plumb from two angles to confirm vertical accuracy.
Caveats:
Ground markings can erode in rain cover with plastic or re-mark if delayed. Always cross-reference with engineering plans to avoid missing offset piers (e.g., for decks).
Step 6: Check Engineering Plans Thoroughly
One near-mistake:
Assuming uniform pier spacings. Always cross-check locations, spacings, and depths against engineering drawings (not just floor plans). Variations occur (e.g., closer spacing under load-bearing walls, deeper near septic or trees).
Tips:
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Print large-scale drawings and highlight piers.
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Use a checklist: location, depth, diameter, reinforcement.
Caveats:
Plans may update post-approval confirm with your certifier. Misreading can lead to re-drilling, costing thousands.
Step 7: Drilling Pier Holes - What to Expect
Pier drilling involves using an auger on an excavator to bore holes. It seems simple but faces challenges like rock layers, tree roots deflecting the auger, or loose soil at the base.
Tips:
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Drill test holes to assess soil/rock adjust auger size if needed.
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Have a spotter guide the operator for plumb alignment (use a spirit level on the auger).
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Drill in stages, pausing to clear spoil and check depth with a tape.
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Let the auger do the work as you drill, dirt will pile up around the rim of the hole (the "spoil pile"). Instead of shovelling this away manually, simply push or kick this loose dirt back into the hole between passes. The auger will pick it up on the next plunge and lift it out for you.
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Re-run strings after each few holes to detect drift.
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Lodge an enquiry with Before You Dig Australia (BYDA) at www.byda.com.au or call 1100
Caveats:
Wet soil can cause hole collapse pump/bucket out water if needed. Rock may require a rock auger or breaker, adding time/cost. Off-centre holes? Widen slightly (e.g., to 500mm) and realign rather than abandon.
Step 8: Depth and Compliance
Our piers:
Mostly 1.5m, 2.0m near septic. For 1.5m raised floors, extra reinforcement was required. Depths vary by state, soil class (e.g., deeper in Class H/E reactive clays), and site conditions.
More Info:
AS 2870 Appendix G specifies minimum depths based on soil tests aim for bearing capacity.
Tips:
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Measure depth from finished ground level, accounting for benching.
Caveats:
Over-drilling wastes concrete; under-drilling fails inspection. Always get engineer sign-off before proceeding.
Step 9: Reinforcement Cages: DIY vs Prefab
Prefab cages weren't available, so we DIY-ed with spiral ties and N12 vertical bars several hours for 20 piers. Mark spacings first to speed up. Budget $500–$700 for a raised system. Engineer inspects before pour.
More Info: Reinforcement depends on footing type: Required for bored piers in most residential cases under AS 2870 (e.g., >1m depth, reactive soils, or to handle shear/bending). Not always needed for shallow, mass concrete piers in stable Class A/S soils. Cages provide tensile strength, preventing cracking under loads.
Tips:
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Assemble on flat ground; use wire ties at every intersection.
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Leave cages 50-100mm short for easy lowering—suspend with rebar chairs.
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Prefab if possible for speed and consistency.
Caveats:
DIY risks non-uniform spacing, failing inspection. Only use if engineer approves—over-reinforcing wastes money, under-reinforcing risks failure.
Step 10: Setting Formwork for Pier Tops
For uniform tops:
Use 500x500mm timber boxes (or sonotubes for round piers), staked firmly, and centred via string marks on edges.
More Info:
Formwork creates a square/round pad for stump brackets, ensuring level connection to bearers.
Tips:
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Brace forms against wind/movement.
Caveats:
Poor staking leads to blowouts during pour. In wet areas, use waterproof forms to prevent slump. Comply with AS 3610 for formwork standards.
Step 11: Levelling: Laser vs Spirit Levels
String bubble levels lack precision for foundations opt for a rotary or line laser with staff for consistent readings across piers.
More Info:
Lasers project a level plane, essential for elevated floors under BCA requirements.
Tips:
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Set up on a stable tripod; calibrate daily.
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Use a receiver for outdoor/sunlight accuracy.
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Mark heights on forms before pouring.
Caveats:
Cheap lasers drift—invest in quality (e.g., self-levelling). Battery failure mid-job delays; have spares.
Step 12: Safety & Site Management
Open pier holes pose fall risks (depth/wall collapse).
What we did:
Temporary barricades, covers for rain, marked zones for trades.
More Info:
Per WorkSafe Australia, secure all voids immediately fences or covers capable of supporting 150kg.
Tips:
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Use high-vis mesh fencing with signs ("Danger: Open Hole").
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Cover with plywood/steel plates secured against movement.
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Never leave unattended; backfill unused holes.
Caveats:
Kids/animals on site amplify risks full perimeter fencing if public access. Rain can cause erosion/collapse; inspect post-storm.
Common Mistakes to Avoid
❌ Assuming uniform pier spacing/depth varies by load/soil.
❌ Tape stretch in heat use steel, measure cool.
❌ No post-drill square checks re-verify strings.
❌ Skipping laser levelling leads to uneven floors.
❌ Pouring without engineer sign-off risks rejection.
❌ Forgetting utilities check hits pipes/cables.
❌ Ignoring soil collapse in wet holes pump/delay.
Recommended Gear for Owner Builders
Basics:
Multiple string lines, star pickets, steel tapes (30m+), spray paint, plumb bob.
Accuracy:
Rotary laser kit (laser, tripod, staff, receiver), long spirit level.
Drilling/Concrete:
Mini-excavator + auger (450mm+ bits, extensions), concrete mixer/vibrator, wheelbarrow, shovels/rakes.
Safety:
Gloves, eye/ear protection, barricade mesh/signs, high-vis vests, hard hats, first-aid kit.
Tips:
Hire heavy gear; buy reusable tools. Check for warranties on lasers.
Caveats:
Cheap augers break in rock rent quality.
Final Thoughts
Foundations demand no shortcuts patience, accuracy, and plan adherence pay off. Get set out and piers right, and the rest of your build flows smoothly.
We're documenting our full owner-builder journey (mistakes included) to help others in Australia save time, money, and stress.
Take it slow, consult your engineer, ask questions, and enjoy the process! Check out our YouTube channel @MyOwnerBuild for video updates and tutorials on our affordable home build.
Beau & Chris