The Australian Standard has Changed

AS 2870-2011 (Residential Slabs & Footings) was published in February 2011. It is critical for all relevant parties to be aware that the BCA (Building Code of Australia) will take up the new AS 2870 from early-mid next year.

This latest release has seen a number of changes introduced which will in turn affect the current design calculations for residential slabs-on-ground.

Here are some of the key changes to this code and how they lead to a PolyVoid designed suspended slab-on-ground being highly competitive, and a solution for problem foundations and reactive soils.

Changes to Building Site Classifications

The following is the most recent soil classification table, based on the Australian Standard for Residential Slabs & Footings (AS2870-2011):


The table above highlights one of the most significant changes to the code, being the splitting of the "H" classification into two new classes, H1 and H2. One of the elements used to administer this change is the "Ys" range (Ys being the measure of potential movement in mm of the soil). A soil's Ys rating is its indication of movement potential. It is measured in millimetres and suggests the value of which the soil might move due to changes in moisture.

Steel Reinforcing Calculations

Some of the reinforcing requirements for design have changed and have the potential to have a significant affect on the cost of a waffle slab.

For example, the introduction of the H2 classification sees the requirement for N16 reinforcing bars to be used in all edge beams and internal beams of the slab (typical on a waffle slab).

There has also been a revision of the mesh requirements for 'slab length'. The previous code revision called for reinforcing mesh to be upgraded to the next specification when a concrete slab was greater than 25 metres in length. The upgrade requirement is now for any slab greater than 20 metres in length. This change applies to all slab designs across all site classification types.

Tree Effect and Cut & Fill

There have also been changes made to the method by which engineers need to calculate "tree effect" and site "cut & fill". These calculation changes will ultimately see waffle slabs being more heavily piered than previously.

These changes will also see the cost of a "conventional" waffle go up as more piers will be specified in order to satisfy the new requirements of the code.

More Code Information

To understand more about how the changes to AS 2870 may affect your slab designs and consequently, slab costs, contact your engineer.

For more information about AS 2870-2011, click here: