Slab Heave, Reactive Soil and Poor Drainage: Who Is Responsible When a New Home Starts to Move?

Building or buying a new home should provide peace of mind. The last thing an owner expects is to see cracked walls, jammed doors, uneven floors, movement in the slab, or signs that the foundations of the home may be reacting to water in the soil.

Unfortunately, slab heave and foundation movement are common issues in domestic building disputes across Victoria, particularly in areas with reactive clay soils.

These disputes are often complex because builders, engineers and insurers may point to “owner maintenance” as the cause of movement. However, in many cases, the real issue may be whether the home was properly designed and constructed to deal with foreseeable soil and drainage conditions from the beginning.

At Boutique Lawyers, we regularly see domestic building disputes where the cause of slab movement cannot be understood by looking at the slab alone. The better question is often:

Was the site properly designed to manage water?

What is slab heave?

Slab heave occurs when the ground beneath or around a concrete slab moves, causing the slab to lift, fall, twist or distort.

In many cases, this movement is caused by changes in moisture content in reactive soil. When reactive clay becomes wetter, it can expand. When it dries, it can shrink. If that movement is uneven, it can place stress on the slab and the building above it.

Common signs of slab heave and foundation movement include:

• cracking to internal or external walls;
• doors and windows sticking or no longer closing properly;
• uneven or sloping floors;
• cracking to tiles, cornices or plasterboard;
• gaps around skirtings, architraves or window frames;
• plumbing or drainage issues;
• visible movement around the edge of the slab.

The issue can be financially and emotionally draining for owners, particularly where the home is new or recently built.

Why drainage matters

Slab heave is often treated as a structural footing issue. That is only part of the story.

A slab sits on soil. Soil is affected by water. If the drainage around a home is not properly designed, installed and maintained, changes in soil moisture may cause movement.

This is why drainage should not be treated as an afterthought.

AS 2870 deals with residential slabs and footings, including site classification and footing design for single dwelling houses. However, stormwater and subsoil drainage are dealt with separately. AS/NZS 3500.3 deals with stormwater drainage, including roof drainage, surface drainage and subsoil drainage systems.

That distinction matters in a building dispute.

A builder or engineer may say that the slab was designed to AS 2870. But that does not necessarily answer whether the overall site was properly designed to manage surface water, stormwater or subsoil water.

The missing issue in many domestic building disputes

In many new home contracts, owners are given general documents about foundation maintenance after completion.

There is nothing wrong with educating owners about maintaining drainage and landscaping. Owners do have responsibilities after they take possession of a home.

However, there is an important legal difference between:

1. maintaining a properly designed and constructed home; and
2. being expected to install or retrofit drainage measures that should arguably have been included before handover.

If the site was reactive, drainage-sensitive or vulnerable to moisture variation, then the builder and design team may need to explain what was done during design and construction to manage that risk.

It should not automatically be assumed that movement is the owner’s fault simply because a maintenance document was provided.

AS 2870 is not the whole answer

In slab heave disputes, builders and engineers often rely heavily on AS 2870.

AS 2870 is clearly important. It is the Australian Standard commonly used for residential slab and footing design. But it is not a complete answer to every water, drainage or soil moisture issue.

Where a home is affected by slab heave, the relevant investigation should usually include:

• the soil report;
• the footing/slab engineering design;
• the site classification;
• the stormwater design;
• any surface drainage plan;
• any subsoil drainage design;
• plumbing compliance certificates;
• site levels and falls;
• landscaping and paving works;
• evidence of leaks, ponding or concentrated discharge;
• whether water was directed away from or toward the slab;
• whether drainage was properly connected to a lawful point of discharge.

In Victoria, stormwater drainage work must comply with the relevant plumbing and drainage standards unless a performance solution is used. This is why the drainage documents should be reviewed carefully in any slab heave or foundation movement dispute.

Why this matters legally

Slab heave cases are rarely simple.

The builder may blame the owner. The engineer may blame maintenance. The plumber may say the stormwater was connected. The geotechnical engineer may point to reactive soil. The owner may be left with a cracking home and no clear answer.

This is where legal strategy and expert evidence become critical.

A proper building defect claim should not only ask whether the slab moved. It should ask why the slab moved, whether the movement was foreseeable, and whether the builder, engineer or other consultant failed to properly address the risk.

In Victoria, these issues may raise questions about statutory warranties under the Domestic Building Contracts Act 1995 (Vic), including whether the works were carried out:

• in a proper and workmanlike manner;
• with reasonable care and skill;
• in accordance with the plans and specifications;
• in accordance with the law;
• using materials that were good and suitable;
• so that the home was reasonably fit for its intended purpose.

Where slab heave is caused or contributed to by poor design, poor drainage, defective construction, inadequate site preparation or non-compliant stormwater works, the owner may have a claim against the builder, engineer, plumber, building surveyor or other responsible party, depending on the evidence.

The problem with blaming trees and landscaping too quickly

Trees, gardens, paving and landscaping can affect soil moisture.

However, in our view, these issues should not be used as a blanket excuse to avoid proper investigation of the original design and construction.

Before an owner is blamed, the following questions should be asked:

• Was the site properly assessed before construction?
• Was the soil classification correct?
• Was the drainage design adequate for the site?
• Were surface water and subsoil water properly considered?
• Was water being concentrated near the slab edge?
• Were stormwater drains properly designed and installed?
• Was there any leaking plumbing or defective drainage?
• Did the builder leave the owner with a site that was vulnerable to movement?
• Were the owner’s alleged maintenance obligations clearly explained and practically capable of being performed?

These questions are particularly important in growth corridors and suburbs where reactive clay soil is common.

What homeowners should do if they suspect slab heave

If you suspect slab heave, do not wait until the damage becomes severe.

Owners should consider taking the following steps:

3. photograph all cracking and movement;
4. keep a timeline of when the damage first appeared;
5. obtain the contract, plans, specifications and engineering drawings;
6. request the soil report and footing design;
7. obtain plumbing and drainage compliance documents;
8. check whether there is a site drainage plan;
9. avoid carrying out major rectification works before obtaining advice;
10. obtain legal advice before communicating extensively with the builder, insurer or engineer;
11. obtain independent expert evidence from the right expert.

The correct expert will depend on the facts. In some cases, an owner may need a structural engineer. In others, the more important expert may be a geotechnical engineer, drainage expert, plumber, civil engineer or building consultant.

What builders should learn from slab heave disputes

For builders, the lesson is clear.

Do not assume that providing a homeowner maintenance guide will protect you from liability if the home was not properly designed or constructed for the site conditions.

Builders should ensure that:

• the soil report is properly obtained and understood;
• the footing design is appropriate for the site classification;
• stormwater and surface drainage are properly designed;
• subsoil drainage is considered where required;
• site levels and falls are properly documented;
• drainage works are compliant and certified;
• owners are clearly informed about any genuine maintenance requirements;
• any departures from the design are properly approved in writing.

A slab heave dispute can be extremely costly. Early legal and expert advice can make a significant difference.

Why expert evidence is critical

Slab heave and foundation movement disputes are technical cases.

It is usually not enough for an owner to say, “My house is cracking.” It is also not enough for a builder to say, “The owner failed to maintain the property.”

The successful party will usually be the party with the clearer expert evidence.

Good expert evidence should address:

• the likely cause of movement;
• whether the movement is ongoing;
• whether the slab and footing design was adequate;
• whether the drainage design was adequate;
• whether the stormwater system was compliant;
• whether the owner’s conduct contributed to the damage;
• what rectification works are required;
• whether the proposed rectification is reasonable and proportionate;
• the cost of repair.

In VCAT building defect proceedings, expert evidence is often the difference between a strong claim and a weak claim.

The bigger question: was the home fit for purpose?

The real issue in many slab heave cases is not whether the owner could have maintained the property better after handover.

The bigger question is whether the builder delivered a home that was reasonably fit for its intended purpose in the first place.

A new home should not require an owner to immediately carry out major drainage upgrades, civil works or expensive moisture-control measures to prevent movement.

If those works were necessary because of the site conditions, then there is a serious question as to why they were not included in the design and construction before completion.

Conclusion

Slab heave should not be treated as just a footing issue, just a maintenance issue or just an owner problem.

In many domestic building disputes, slab movement may involve a combination of reactive soil, poor drainage, inadequate design, defective construction, plumbing issues and insufficient expert investigation.

For homeowners, the key is to obtain the right advice early and preserve the evidence.

For builders and consultants, the key is to ensure that soil conditions, drainage and slab design are properly considered before the home is built.

For lawyers, the key is to frame the dispute properly. The strongest cases will often be those that connect the technical evidence to the legal obligations: soil conditions, drainage design, slab performance, statutory warranties and the real impact on the owner.

In slab heave disputes, the question is not only whether the house has moved. The question is why it moved — and whether it should have been prevented.

Need advice about slab heave or a building defect dispute?

Boutique Lawyers are specialist building and construction lawyers in Melbourne. We act for homeowners, builders, developers and industry professionals in complex domestic building disputes, building defect claims, VCAT proceedings, negligence claims and construction litigation.

If your home is affected by slab heave, cracking, drainage issues, foundation movement or defective building work, contact Boutique Lawyers for advice about your rights and options.

Call 1300 556 140 or contact Boutique Lawyers to speak with a building and construction lawyer in Melbourne.

Disclaimer

This article is general information only and is not legal advice. Slab heave and building defect disputes are highly fact-specific. You should obtain legal advice about your particular circumstances.