Settlement Status
ACCEPTABLE
Within AS 2870 tolerances
Calculate allowable settlement and differential movement
Free Australian foundation settlement calculator. Assess total and differential settlement, determine structural risk, and estimate repair costs based on AS 2870 engineering standards for 2026.
Professional engineering assessment for residential and commercial foundation movement
Calculate total and differential foundation settlement based on soil conditions, building loads, and time factors. Our calculator applies Australian Standard AS 2870 criteria for residential slabs and footings, determining whether observed movement falls within acceptable tolerances or requires remedial action.
Assess structural damage risk from foundation settlement including wall cracking, door jamming, floor slopes, and roof distortion. Understand the relationship between differential settlement magnitude and building damage severity following Engineers Australia guidelines for foundation performance evaluation.
Estimate foundation repair costs for underpinning, reblocking, slab jacking, pier installation, and remediation works. Get 2026 Australian pricing for various repair methods based on settlement severity, soil type, and building characteristics to budget accurately for foundation restoration.
Enter foundation and settlement measurements
No Settlement
Uniform Support
Uneven Settlement
Structural Stress
Differential settlement causes building tilt and structural distress. Level foundations maintain uniform support while settled foundations create stress points leading to cracks, door jamming, and structural damage.
Foundation settlement occurs when soil beneath a building compresses or consolidates under structural loads, causing the foundation to move downward. All foundations experience some settlement immediately after construction as soil adjusts to new loads. This initial settlement is typically harmless if uniform across the structure. However, differential settlement—where one part of the foundation settles more than another—creates stress in the building frame causing cracks, floor slopes, and structural damage.
Australian Standard AS 2870 provides guidelines for acceptable foundation movement in residential construction. Total settlement up to 40mm is generally tolerable if uniform, but differential settlement exceeding 1:300 angular distortion (10mm over 3 metres) typically causes visible damage. Settlement severity depends on soil type, foundation design, building stiffness, and time since construction. For comprehensive foundation standards, consult the Australian Building Codes Board for residential construction requirements.
Essential Terms: Total settlement is maximum vertical movement at any foundation point. Differential settlement is the difference between highest and lowest points. Angular distortion (deflection ratio) is differential settlement divided by distance between points. AS 2870 limits angular distortion to 1:300 for acceptable residential performance, with 1:500 providing minimal visible damage.
Australian Standard AS 2870 establishes performance criteria for residential slabs and footings based on acceptable damage thresholds. These limits balance structural safety, aesthetic appearance, and repair economics. Buildings designed to AS 2870 should accommodate predicted soil movements without exceeding serviceability limits causing unacceptable damage or loss of function.
| Damage Category | Angular Distortion | Differential (6m span) | Visible Effects | Action Required |
|---|---|---|---|---|
| Negligible | 1:500 or less | Up to 12mm | No visible damage, hairline cracks possible | None - Monitor |
| Very Slight | 1:500 to 1:350 | 12-17mm | Fine cracks in walls, doors may stick slightly | Monitor Annually |
| Slight | 1:350 to 1:300 | 17-20mm | Noticeable cracks, minor door/window issues | Cosmetic Repair |
| Moderate | 1:300 to 1:150 | 20-40mm | Significant cracks, doors jam, floor slopes visible | Structural Assessment |
| Severe | Greater than 1:150 | Over 40mm | Major structural distress, safety concerns | Urgent Remediation |
AS 2870 classifies soils from Class A (stable, minimal movement) to Class E (extremely reactive, high movement potential). Reactive clay soils expand when wet and shrink when dry, causing significant seasonal foundation movement. Non-reactive soils like sand and rock remain dimensionally stable providing reliable foundation support with minimal settlement risk.
Soil Types: Sand, rock, non-reactive clay
Movement Potential: Very low (<20mm)
Characteristics: Minimal seasonal movement, excellent bearing capacity
Foundation: Simple slab or strip footings adequate, low settlement risk over building lifespan
Soil Types: Clay soils with moderate shrink-swell
Movement Potential: Moderate (20-40mm)
Characteristics: Seasonal movement, moisture-dependent
Foundation: Stiffened raft slab required, careful drainage design, anticipate moderate settlement potential
Soil Types: Highly plastic clay, black/grey clays
Movement Potential: High (40-70mm+)
Characteristics: Significant expansion/shrinkage cycles
Foundation: Deep waffle raft or pier systems, extensive ground preparation, high settlement and heave risks
Foundation settlement results from soil consolidation under building loads, moisture changes in reactive clay, erosion, tree root action, or defective construction. Understanding the cause is essential for effective remediation. Settlement may occur rapidly after construction or develop gradually over years as soil conditions change or building loads increase.
Identify Active Movement: New cracks appearing or existing cracks widening, doors/windows progressively harder to open, floor slopes increasing over time, gaps opening between walls and ceilings. Active settlement requires urgent investigation and monitoring to determine cause and appropriate remediation. Static old cracks without progression typically don't require repair beyond cosmetic patching.
Foundation repair options range from simple crack filling for minor cosmetic issues to extensive underpinning for severe structural settlement. Repair selection depends on settlement severity, ongoing movement activity, soil conditions, and building characteristics. Professional geotechnical and structural engineering assessment is essential for settlements exceeding AS 2870 limits before commencing remedial works.
Australian foundation repair costs in 2026 vary significantly based on method, access, soil conditions, and building configuration. Simple crack repairs cost $500-2,000 while major underpinning projects reach $30,000-100,000+ for extensive work. For related foundation issues, check our allowable bearing pressure calculator for soil capacity assessment requirements.
Cost: $500-3,000
Settlement: Negligible to very slight
Methods: Crack filling, patching, repainting
Suitability: Static cracks, no active movement, cosmetic damage only. Does not address underlying settlement causes.
Cost: $8,000-25,000
Settlement: Slight to moderate
Methods: Limited pier installation (4-8 piers), slab jacking, resin injection
Suitability: Localized settlement, single room or corner, accessible areas, stable soil at depth allowing effective pinning.
Cost: $25,000-100,000+
Settlement: Moderate to severe
Methods: Extensive pier systems (12-30+ piers), full perimeter underpinning
Suitability: Widespread settlement, reactive clay sites, multi-room damage, requires engineering design and certification.
Cost: $50,000-150,000+
Settlement: Severe or beyond repair
Methods: Complete slab removal and rebuilding, upgraded foundation system
Suitability: Catastrophic failure, extensive cracking throughout, waffle raft collapse, more economical than extensive underpinning in some cases.
Accurate settlement measurement requires leveling surveys comparing current elevations to original construction levels or baseline measurements. Professional surveyors use optical or laser levels achieving millimetre precision. DIY monitoring using spirit levels and string lines provides approximate indication but lacks accuracy for engineering assessment. Measure at multiple points across foundation perimeter and interior to identify differential settlement patterns.
Effective Tracking: Establish baseline measurements at multiple foundation points. Photograph and measure all cracks noting width, length, and location. Re-measure every 3-6 months initially, then annually if stable. Document drainage changes, tree growth, and water leaks. Monitor doors and windows for increasing binding. Professional surveys recommended for insurance claims or litigation providing legally defensible measurement records.
Preventing foundation settlement is more cost-effective than repair. Proper site preparation, appropriate foundation design for soil class, effective drainage, and careful vegetation management minimize settlement risk. New construction should follow AS 2870 requirements for soil investigation, foundation design, and construction supervision ensuring adequate protection against predicted soil movements.
AS 2870 allows up to 40mm total settlement for residential buildings if uniform. Differential settlement should not exceed 1:300 angular distortion (20mm over 6 metres) to avoid visible damage. Settlements under 1:500 angular distortion (12mm over 6m) typically cause negligible damage requiring no repair. Settlements exceeding 1:300 cause significant cracking, door jamming, and floor slopes requiring structural assessment and potential remediation.
Angular distortion = Differential Settlement ÷ Distance Between Points. Example: 20mm settlement over 6 metres = 20mm ÷ 6000mm = 1/300 or 1:300. Measure height difference between two foundation points and divide by horizontal distance between them. Lower ratios (1:500) indicate less distortion than higher ratios (1:150). AS 2870 uses 1:300 as the threshold for acceptable residential performance.
Differential settlement results from uneven soil conditions beneath foundations including variable soil types, non-uniform compaction, tree root moisture extraction on one side, localized water leaks, or inadequate footing depth in some areas. Reactive clay soils experiencing different moisture contents cause uneven foundation movement. Poor construction practices like inconsistent concrete placement or insufficient reinforcement contribute to differential settlement problems.
Foundation underpinning costs $8,000-25,000 for minor work (4-8 piers) or $25,000-100,000+ for extensive projects (12-30+ piers) in 2026. Factors affecting cost include number of piers required, soil conditions, access difficulties, building height, and pier depth needed to reach stable soil. Pier costs average $2,000-4,000 each installed. Slab jacking costs $3,000-12,000 for localized lifting. Always obtain multiple quotes from licensed foundation repair contractors.
Standard home insurance typically excludes gradual settlement, ground movement, and soil issues. Insurance may cover sudden settlement from specific events like burst pipes, storm damage, or earthquakes if you have appropriate coverage. Reactive soil movement, natural consolidation, tree root damage, and poor construction are generally not covered. Review your policy and consider obtaining geotechnical reports documenting settlement causes for insurance claims.
Purchase houses with settlement only after professional structural and geotechnical assessment. Obtain engineering reports quantifying settlement severity, cause, progression rate, and repair costs. Static settlement within AS 2870 limits (under 1:300 angular distortion) with no active movement may be acceptable with price adjustment. Active progressive settlement, severe differential movement (over 1:150), or unknown causes present high risk requiring either substantial price reduction or purchase avoidance. For assistance with foundation analysis, use our bearing pressure calculator for soil assessment.
Most foundation settlement occurs within first 1-2 years after construction as soil consolidates under building loads. Initial settlement typically completes within 3-5 years in stable soils. Reactive clay sites experience ongoing seasonal movement throughout building life with magnitude depending on moisture variations. Existing buildings on stable soils should show minimal new settlement unless triggering events occur (tree planting, drainage changes, major renovations). Settlement appearing years after construction indicates problems requiring investigation.