Site works and slab foundation are very often a grey area when budgeting for your house in difficult soil conditions, and when not done correctly can cost you thousands of dollars.

To get a better understanding of the soil conditions your site will need to be tested by a geotechnical engineer, who will take soil samples from the site, subject them to varying tests and then specify the correct site classification according to Australian Standard AS 2870/2011 - Residential slabs and footings. This rating indicates how reactive the soil is, and will help your structural engineer to determine what sort of footing system is suitable for your site.

Below is a list showing what those ratings represent

 Class A (0-10mm)        Stable, non-reactive. Most sand and rock sites. Little or no ground movement likely as a result of moisture changes.


Class S (10-20mm)      Slightly reactive clay sites. May experience slight ground movement as a result of moisture changes.


Class M / M-D (20-40mm) Moderately reactive clay or silt sites. May experience moderate ground movement as a result of soil conditions and moisture changes.

Class H1 / H1-D (40-60mm) Highly reactive clay sites. May experience a high amount of ground movement as a result of soil conditions and moisture changes.

Class H2 / H2-D (60-75mm) Highly reactive clay sites. May experience very high ground movement as a result of soil conditions and moisture changes.

Class E / E-D (75mm+)         Extremely reactive sites. May experience extreme amounts of ground movement as a result of soil conditions and moisture changes.

Class P (this is approximately 70% of building sites in Australia)         Problem sites. The ability of the soil to evenly bear a load is very poor. Sites may be classified as 'Class P' as a result of mine subsidence, landslip, collapse activity or coastal erosion (e.g. dunes), soft soils with a lack of suitable bearing, cut and/or filled sites, or creep areas. 


One of our most recent projects in Perth Hills came back as Soil class P due to preexisting loose fill on the site and reactive clay.

Recommendation from the geotech engineer was to remove the top soil to the cut base and prepare an 800mm deep sand pad as per the requirements for this type of site class. This seemed not very extraordinary at start but only when we started getting quotes we realized to get the sand pad done the fees ranged in areas of $20k which put the whole project at risk of going over budget.

Determination and our extensive research to find more affordable way of doing the slab construction has been very fruitful once we have found The CUPOLEX® system, which uses 100% recyclable plastic interlocking domes to create concrete foundations with exceptional strength, yet using less concrete, less steel and less labour.

The CUPOLEX® system  together with their THERMAL WRAP®, is specifically designed for the environmentally conscious and those with energy efficiency in mind.


What are the CUPOLEX® benefits and how have we managed to reduce the costs?

-The system can provide significant reductions in the volume of concrete, reinforcing steel and labor required to put the system down.

-It can be easily adapted to any soil classification

-One pallet of Cupolex replaces 3-4 trucks of gravel or fill

-The Cupolex system allows Volatile Organic Compounds (VOC’s), Radon Gas and humidity or moisture to be passively vented away from the slab

-There is an option to upgrade the thermal efficiency of slab with their THERMAL WRAP®

Oxley Home is a first home in Perth where we used the CUPOLEX® dome technology and THERMAL WRAP®, and we believe this product can present a great alternative and cost effective solution for sites with reactive site classification.

What else have we learned from this experience? Always take a second opinion! Finding a good Geotechnical and structural engineer is very important and should be treated as such. Ask your designer for recommendation and make sure they are open minded to new and innovative ideas.

For further information about the CUPOLEX® system and its benefits combined with modular panels please send us an email at‍

You can also view a video on how it was done here