So you've finally built your new home. Congratulations! Now let's make sure it stays standing for the long haul. Cracked walls, sloping floors and doors that won't close are the stuff of homeowner nightmares, and most of them start in the ground.
Your foundations carry the whole weight of the house, so any movement in the soil around them spells trouble. An aircon dripping onto the soil, a big tree planted too close or a garden bed built against the slab may seem harmless. Over time, they can make the soil swell, shrink and move in ways that seriously damage your home.
Here's how to spot the early signs of foundation damage and the common culprits that catch new homeowners by surprise. An ounce of prevention is worth a pound of cure.
C5 - Pre Pour Slab Inspection Checklist
$119.00 AUD
Last updated 28 Oct 2026 · Revision 4 · Free updates for life
Checklist Type: Major (Base Stage)
Form Factor: Fillable, print-ready PDF (A4, 30 pages)
When to use: Base stage: after the slab is prepped, before concrete is poured
A 95-point pre-pour slab checklist. Check setbacks, boxing, membrane, pipes and steel after the slab is prepped and before concrete is poured, while fixes are still simple.
What Is Soil Movement and How Can It Damage Foundations?
Soil movement refers to shifts in the foundation soil that supports your home. There are a few types you need to watch out for:
Heave
Heave occurs when excess moisture causes clay soil to swell, pushing up on foundations. During rainy seasons or if you have poor drainage, the area around your foundation may become saturated. As the clay absorbs water, it expands and lifts your foundation.
Shrinkage
The opposite of heave, shrinkage happens as clay soil dries out and contracts, pulling away from foundations. This often occurs in hot or arid weather. As the clay loses moisture, it shrinks and cracks, damaging foundations by removing vital support.
Slope failure
If your home is built on a slope or incline, the soil can become unstable over time. Erosion wears away at the slope, while the weight of the structure causes the foundation to tilt or shift downwards. This can lead to subsidence as the soil gives way.
To avoid costly damage:
- Install gutters and downpipes to carry rainwater away from the foundations.
- Install additional yard gullies in areas where water is ponding.
- Limit watering and avoid planting close to foundations. The roots can cause shrinkage and instability.
- Don't dig near the house without advice. Soil under your footings spreads the load outwards at an angle (engineers call it the angle of influence), so a trench too close can undermine them.
- Inspect foundations regularly for signs of movement like tilting, cracks or bowed walls. It’s best to address any issues early.
- Watch your water bill. If it jumps, especially after any digging near the house, you may have a leaking pipe or drainage connection wetting the soil and making it swell.
Keep a close eye on the ground your house is built on. It's the cheapest insurance you'll get.
The Hidden Threat: Aircon Overflow Pipes
The hidden threat you need to watch out for is your air conditioning overflow pipe.
Where is it and why should you care?
Your AC unit produces condensation which needs to drain somewhere. The overflow pipe directs the water away from the unit to avoid damage. The problem is these pipes often drain right next to the foundation of your home.
- Excess water from the overflow pipe can saturate the soil surrounding your foundation, causing the ground to swell and put pressure on the structure. This can lead to cracks in walls and floors, doors and windows sticking or not closing properly, and uneven or sloping floors.
- The overflow water also makes its way under the foundation, eroding the soil and compromising the support for your footings. This erosion can cause foundations to drop and tilt, damaging the building above.
To avoid this, have a plumber connect the condensate drain to the stormwater system. Re-grade the soil so it falls away from the house, and seal any cracks in the slab edge or walls.
Don't Plant Trees Too Close to Your Home's Foundations
One of the biggest mistakes homeowners make is planting trees too close to the house. Trees add street appeal, but their roots go looking for water, and the soil under your footings is often where they find it.
As roots grow towards foundations, they absorb moisture from the soil. This causes the soil to shrink, reducing support under the footings. The foundations are then at risk of subsiding, leading to cracks in walls and floors. Severe cases can undermine footings entirely.
The roots also exert an upward pressure on footings as they grow, which can lead to heaving and tilting of the foundation. This damage may not be noticeable for many years but will be expensive to repair. It's best to avoid it altogether by planting trees a safe distance from foundations.
On reactive clay sites, keep a single tree at least its mature height away from the house, and one and a half times its mature height for a group of trees. That's the CSIRO's guidance in BTF 18, Foundation Maintenance and Footing Performance. Ask your local nursery for non-invasive species that suit your area, and check how tall they'll grow.
If you have existing trees too close to your home, you may need to remove them to prevent damage, especially if you notice cracks appearing in walls and floors. Removal of established trees should only be done by a professional to avoid damage to property or injury. In some cases, root barriers can be installed to redirect roots away from foundations, but their effectiveness depends on the tree species and soil conditions.
Building Garden Beds Near Foundations - Do It Right
Building garden beds near the foundation of your home may seem like an innocent enough activity, but it needs to be done properly to avoid potential issues. The soil around foundations is sensitive, and making changes to it can lead to damage if you're not careful.
There are a few things to keep in mind when installing garden beds close to your foundation.
Provide adequate drainage
Make sure the garden bed allows for sufficient drainage and airflow. Standing water is one of the biggest threats to foundations. Provide a slope away from the house so water flows away, and consider installing drainage pipes if needed. Also, choose plants that do not require frequent or excessive watering.
Leave adequate space
Don't build garden beds against the slab. Leave at least 1 to 2 metres between the bed and the house so you can inspect and maintain the foundation, and so roots don't grow under it. Garden beds, mulch or paving built up against the slab edge can also cover the termite inspection zone and bridge your termite barrier, which can void the barrier warranty. Keep the slab edge exposed.
Choose plants wisely
Choose plants, trees and shrubs with non-invasive roots. Aggressive roots dry out the soil and damage foundations. Do your research before you plant, and avoid plants with dense, woody root masses.
Soil barriers
For additional protection, install a vertical barrier in the soil between the garden bed and the foundation. Materials like concrete, metal or PVC can block plant roots and also help prevent excess moisture from seeping into the foundation soil.
A garden bed near the house doesn't have to be risky. Good drainage, enough space, the right plants and a root barrier will protect your home.
Water Wisely - Avoid Overwatering Near Foundations
Water your garden and lawn wisely, especially the areas around the foundation of your home. Overwatering the soil surrounding foundations can lead to costly damage.
Watch for Signs of Movement
Keep an eye out for tilting, cracks in walls, doors or windows that stick or won’t close, or sloping floors which can indicate foundation movement from oversaturated soil. Foundation damage like this can be expensive to fix, so it’s best to prevent it.
Water Infrequently and Avoid Excessive Amounts
Only water when the top few centimetres of soil are dry (stick your finger in to check). When you do water, water less often but deeply, soaking the soil 15 to 20cm down. Let excess water drain away from the house, and never leave water standing against the slab.
Improve Drainage
Make sure downpipes are connected to the stormwater drainage lines and direct water away from the base of the foundation, ideally into yard gullies. Plant gardens, shrubs and trees at least 1 to 1.5 metres away from foundations. Their roots can absorb moisture from the soil and cause shrinkage next to the foundation.
Choose Drought-Resistant Plants
Select plants, shrubs, trees, and grass types that don’t require frequent or heavy watering, especially within 1 to 1.5 metres of foundations. Drought-resistant greenery will help ensure the soil in these areas does not become oversaturated.
The Bottom Line
Five things to keep an eye on:
1. Keep aircon condensate out of the soil next to the house.
2. Plant trees well away from the house: at least their mature height on reactive clay.
3. Keep garden beds and mulch off the slab edge.
4. Water wisely and keep water flowing away from the house.
5. Don't dig near your footings without advice.
If you notice cracks appearing, get a professional to inspect without delay.
