Site Drainage
Extremes of wetness or dryness should be prevented on sites classified as either E, H or M and it is essential that drainage or gradient away from the building line is in place and maintained for the economic life of the building, to prevent water ponding against or near the building line. This is a requirement under the National Construction Code and Australian Standard for stormwater related drainage (AS: 3500).
This has particular relevance to slab on ground structures, especially where brick or masonry walls are concealed into the ground onto a concrete footing. Ponding water occurs where there is inadequate catchment and run-off stormwater drainage. This moisture can cause changes in the soil around concrete footings and soil expansion following by shrinkage can result in movement due to the corresponding shift in weight from the wall/structure above. This movement may evidence itself by way or cracking, deviation or drop from a straight line and in the case of a wall, a widening separation gap, and rotation.
In all cases, all stormwater should be collected and diverted away into either Council approved drainage points or stormwater pits within the ground, provided they are constructed in a manner that is in compliance with the requirements of the Australian Standard. These are often referred to as a gravel soak hole, usually 1.5 meters cubed, strategically placed within the block and are used because it is not practical and possible to get the stormwater from the block to a Council stormwater drainage outlet – usually for houses that are lower than the Road frontage and/or Council drainage point. With older dwellings, it is not unusual to find downpipes discharging water directly onto the ground in which case the water normally gravitates to lower areas. Obviously this is not desirable and for modern construction not compliant, as there may be a non-wood flow to neighbouring properties causing some deterioration or inconvenience to them. To the best of our knowledge, there is no current statute requirement all or making a property owner upgrade if this is the case where downpipes do not connect continuously to a drainage point however obviously in the event of any legal action from a neighbouring property there may be an enforcement put on a property owner to address any stormwater issue the property may be causing a neighbour. It is always advisable that good stormwater drainage in place, not only to provide the best levels of protection for the property itself, but also for adjoining neighbours. We recommend you seek the qualified advice of a QBCC licensed plumber or drainlayer so you can receive the most optimum advice in relation to this area of the property and the Australian Standard for plumbing and drainage, should you choose to peruse it, is AS:500: 2015.
Local authorities provide details of known flooding relative to all properties in their municipality and this may/may not restrict any such formal development. In the cases you should seek the advice of the local Council authority in relation to your property and if it is subject to any flooding, either from Overland flow or flood/river waters. For any intended development of a block, a formal development application or building approval lodgement would normally have to be done, issued by a QBCC licensed building certifier and obviously any local authority restrictions/requirements would have to be complied with. There are often impediments and restrictions imposed on construction where there are known overland flows and blocks that are subject to water exposure during either storm water events or flooding.
Around 13 January 2011, following heavy rainfalls throughout Queensland, the Brisbane River rose to levels not experienced since the 1974 floods and this caused major devastation to many suburbs and thousands of homes and families were severely affected by river flooding. Again, we recommend you immediately seek specialised advice from all recognised authorities, including local and state governments, so that you can be truly and fully informed about all matters in relation to a property and any potential flooding issues or building restrictions that it may have attached on it as a result of being subject to water on occasions. Flood associated matters are excluded from our level of service when we carry out inspections and indeed the scope of the Australian Standard and you must seek further advice from a qualified professional in this area (hydraulic engineer).
South East Queensland can experience sudden storm conditions with concentrated bursts of rain and hail. For this reason, stormwater drainage in place should be capable of dealing with such extreme conditions and it is always better to be safe than sorry. In most cases, owners only discover that a water entry problem exists, during adverse wet weather conditions and should this be the case then rectification drainage will have to be installed. It is for this reason that you must be proactive and not reactive in relation to this area of construction, as poor or inadequate drainage can be absolutely devastating to materials.







All too often during our inspections we identify areas which are conducive to the collection of retained ground moisture near a structure. Elevated moisture levels are known to provide conditions favourable to Timber Pest activity, particularly termites, and it is vital that every effort be made to avoid these risks. The most common causes of retained ground moisture are inadequate surface water drainage, downpipes not connected to drainage outlets, no gutters in place for roofing areas, outlet pipes for air conditioners, relief and overflow valves for hot water cylinders, corroding and join leakages of gutters and downpipes, defective or incomplete flashing and plumbing for rainwater tanks leaking. These are all issues which can be, and should be rectified, if they are in existence at a property.







