According to the Housing Engineering Design & Research Association (HEDRA), it is the homeowner’s responsibility to maintain their garden, paving, drainage systems and foundations. The homeowner should also become familiar with the soil classification at the site and the type of footing system used. This ensures that the footings and dwelling achieve acceptable performance and safety during their design life. Foundation soil moisture should be monitored to minimise the influence of expansive soils.
Ensure a soil test has been undertaken on the site and that the footings are suitable for the soil type. An engineering consultant can be engaged at this stage to check the plans, and may find improvements that can be made to avoid costs down the road. It may be wise to hire a building inspector to inspect the footing construction. The building inspector will look for things like reinforcement positioning and grade, and can oversee the building process to ensure building code requirements are met.
Structures near the dwelling should all have guttering installed to correctly discharge water away from the buildings footings. This includes sheds and outdoor roofed areas. Plumbing should be run away from the dwelling where possible. Paths around the property should have a slope away from the dwelling and no water should be allowed to pool near the footings. In highly reactive clay soils, water should be collected with an appropriate drain and diverted to storm water plumbing. In sloping sites, the use of channel drains and agricultural pipe is strongly recommended.
After Taking Possession of an Existing House
When moving to an existing house, inspect plumbing and footing areas for any signs of leaks. Key places to inspect are stormwater junctions, guttering (for overflows/blockages), hot water relief valves, water tank overflows, air conditioner condensate outlets, and leaking taps. Ensure these water sources are repaired/diverted correctly. Even a slow leak can maintain soil moisture long enough to cause substantial damage.
Trees can cause damage throughout their lifespan and for months after removal. They tend to dry out the soil where they are planted and will chase and often block subsurface plumbing. If you plan on removing a tree close to the building, you should consult an engineer for advice, as this will likely change the local water table. Similarly, letting garden beds dry out or overwatering may cause unwanted shrink or swell behaviour.
If the building experiences differential footing movement due to a change made to soil moisture, the footings will take some time to settle. This period of ‘drying out’ can last from 6 to 36 months depending on the severity of the moisture change, and rate of drying. It is advised that this period elapse before aesthetic repair works are undertaken to avoid repairing cracks that are still moving. A structural engineer will be able to advise on any structural repair works that are necessary after footing movement.
What Not To Do?
Soil moisture levels change throughout the year quite predictably. In the winter months, the soil is generally moister than in summer. Additionally, the side of the property that receives more sun will typically have drier soil too. This means that some level of differential movement is normal throughout the year, and is considered a normal aspect of building construction on reactive soils. In winter, it is more common to observe ‘dishing’ of a structure (where the perimeter footings lift due to moisture), and ‘doming’ in summer (when the perimeter dries out faster than the middle footings).
Floor areas with isolated ‘bounce’ (where the floor is not engaged with the stumps due to shrink/swell), should not be packed at the gap between the bearers and stumps. The danger is that when the next swell cycle occurs, the packing will push the floor higher than normal, and may cause local failure of the soil due to increased loading.
Building garden beds adjacent to a dwelling may look good, but it has potential to hinder footing performance, resulting in costly damage to the dwelling. Garden beds require water- the mortal enemy of footings. Overwatering of garden beds and the use of irrigation systems are common causes of water migration to a subfloor area. The National Construction Code details that a subfloor level shall not be lower than the surrounding natural surface, and that pavements surrounding the dwelling should have a fall of 1 in 20 away from the dwelling. Paving around a dwelling without drainage or adequate slope can lead to unwanted water ingress.
At Rapid Consulting Engineers, we have much experience with footings and the maintenance required. Our consultants have inspected hundreds of dwellings with structural damage to them. Call us today for any queries.