Metamorphs

16/08/2026

I believe that suspended waffle slabs were around before the waffle pod slab & footing system.

With waffle slabs, a reuseable void former, creates a grid of beams tapered in their depth, between which a thin slab spans. This waffle slab is contrasted against the alternative of a thick slab, and the formation of the voids save concrete.

With a waffle pod slab/footing system, the comparison is with a stiffened raft on ground. If lift the stiffened raft system out off the ground and place on top of the ground. Thr first thing to notice is that the beams can no longer vary in depth, they all have to extend down to the ground to provide support. Next the space between beams is no longer infilled with dirt, so a void former is required to create this void in the concrete casting, and otherwise support and form the sides of the beams.

So its an issue of designing and making a mould, pattern or die as may otherwise be referred to in casting and moudling of other materials. The telephone companies have narrow trenching machines for layering cables. Using such trenching machines narrow beams can be made in the ground. However, 110mm is only just wide enough for the human hand to fit, and only just wide enough for the vibrator/compacter used to consolidate the concrete. Deep narrow beams are not practical to install reinforcement into. Also the deeper that go into the ground the more unstable the side walls of the trenches, so shoring becomes necessary. The other issue is that the trenching machine or mechanical shovel has to have somewhere to sit, and be able to reach each of the trenches which have to be dug. The weight of the machinery can collapse the walls of the trenches.

So there are issues to be considered when designing and constructing the mould in the ground or above the ground. (though probably no design takes place) It is to be noted that large metal castings are cast in the ground, and a foundry floor is likely to be dirt, so that moulds can be cut/dug into the ground. So concrete is not unique in being cast in the ground.

Another point to note is that increasing spacing of beams typically doesn't save material. Beams at greater centres need to be bigger to carry more load. Members spanning between the beams have to be bigger to span greater distances. Spanning greater distances will typically add material, whilst changing spacing will typically just redistrubute the material in the members being spaced.

So if double spacing of beams, then double load on the beams, and therefore resistance needs to double. Whilst for the uniformy distributed loads we normally consider, doubling the span, results in a need for 4 times the resistance. So typically want to keep spans low, which means the spacing of supporting members needs to be kept low. A slab on ground is supported by the ground, the slab in a waffle pod system is suspended and spanning between beams. (barring complications of unstable or expansive soils).

Irrespective of maximum spacing permitted for beams, in the NCC/BCA and residential slab and footing code (AS2870), beams need to be under load bearing walls. So starting point is typically laying out beams under the perimeter of the building, and other load bearing walls. If walls don't form a simple rectangle and are stepping in and out, then beams start coming closer together. Then if wish to use waffle pod system, need to fit the grid to the floor plan and get its narrow beams where needed. There is also an issue as to whether these narrow beams have adequate weight to provide hold down againt wind uplift, or otherwise the system has adequate resistance to activate a large area of slab and beams to provide hold down without cracking (to failure).

For a given project need to assess whether 110mmwide beams at 1200mm centres or 300mm wide beams at 4000mm centres is preferable. Whether it is preferable to put the beams in ground, or above ground. Also assess the viability of the construction process.

It is not an automatic given, that the waffle pod system is a lower cost option.

14/08/2026

Interesting though I was more expecting a detailed comparison providing evidence that the waffle pod system is cheaper.

I must be missing something, as I don't see how waffle pods can be lower cost than a stiffened raft. In a stiffened raft beams are typically at 4m centres, 300mm wide and have 2 bars in the top.

A waffle pod system has 110mm beams at 1.2m centres, with 1 bar in the top. So in a 4m width, there is at least 3 beams, creating a total width of 330mm. Each beam 1 bar so, total 3 bars. Whilst each beam has ligatures with 2 vertical legs. So 3 times the vertical legs. So more concrete and more reinforcement in the waffle pod system.

There maybe a saving of concrete in the slab, as it maybe thinner than the 100mm used in the stiffened raft.

The waffle pod system also requires additional labour and materials installing the waffle pods and accessories, then there is additional formwork installed around the edge of the waffle pods, which is taller than the 100mm for the stiffened slab.

The waffle pod system is also above ground, its not keyed into the ground, the beams and slab also provide less hold-down weight at wind tie-down points. May need to bring in soil if need to build up the ground around the waffle slab, to avoid steps and ramps.

Where waffle pods don't fit well into the floor plan, may end up with mass concrete infill.

So all up really need to design and cost both systems, to assess which is lowest cost for a specific project.

But rough guess would if don't need to bring soil in and build up site, then trenching and stiffened raft likely lower cost. Next issue would be checking how much need to raise floor above natural ground level, in which case a suspended slab using steel deck likely better than waffle pods.

That is steel deck like bondec, though preferable something better with a trapezoidal profile which reduces concrete usage. Posts, beams and suspended slab, likely less labour than installing many waffle pods.

Also depending on situation a simple thick slab, whilst using more concrete can involve significantly less labour. Especially small extensions, where floor levels have to match existing, and waffle pods mostly unsuitable.

Also note that a stiffened slab can also have beams at greater than 4m centres. (From memory 6m is possible in some of the standard designs)

Complete guide to waffle pod slab construction in Australia. Costs per m2, slab details, design considerations and when to use waffle pod vs raft slab. Written by a practising QS.

17/03/2026

I'd say the SA planning code is currently flawed and not compliant with the NCC/BCA.

Has I mentioned previously, we have a required to be on the boundary or 600mm away from the boundary, as a basic requirement. As a consequence of energy efficiency drive in the 1970's, 600mm eaves overhangs became popular to block the midday sun and solar gain through windows in summer. Poor designers and checkers resulted in gutters overhanging neighbouring properties. Council devlopment plans later typically had 1m side boundary offset, rear and front boundary offsets (setbacks) are typpically several metres. Now 1m is reasonable it fits with the NCC/BCA requirement of the first 1m of ground adjacent to the building having a fall away from the building.

The SA planning code typically sets at 900mm. Now whilst this would avoid the need for fire rated construction, it is not compliant with the storm water drainage requirements of the NCC/BCA.

The NCC/BCA does not say that the gound adjacent to the building has to have a 2.5% or 5% fall, it states the first metre has to have a 25mm or 50mm fall. If the remaining 100mm of ground is on the neighbours property and falling the opposite direction, it is defective. Not only is the water not draining far enough away, but forming a channel in which water can rise and get closer to the building.

The envelope of the building should be kept well clear off boundaries, to ensure proper access/egress and circulation around the building, as well as ventilation, and proper access to roof gutter and the building for maintenace without need to access neighbours property or lean down from the roof.

The water directed away from the house should also be directed to a proper retention/detention sump/pit/tank, not left ponding on the surface.

08/01/2025

When look at aerial photo's of Adelaide something doesn't look right. We have a planning code and previously development plans, with a fundamental requirement that a building is either on the boundary or 600mm from the boundary. The development plans typically set side boundary offset of 1m, whilst front and rear boundary offsets were much greater. The planning code typically sets 900mm set back, the NCC/BCA sets 900mm setback to avoid fore rated construction.

The problem is that these set backs tend to relate to walls, not the building. The purpose of the 600mm requirement is access to keep the space clean and free from litter, vermin and pests. But should really apply to the building not the wall. House gutters need to be cleaned, and preferably without working from the roof top and with out going into neighbours property. If both neighbours have walls at the minimum then neither can access the gutters, nor the fascia boards.

When both on the boundary there is always a narrow gap between the two walls, which is not capped, If away from boundary, still get a near continuous roof scape and no gap between the roof and the boundary.

The other issue is that there is meant to be minimum open space requirements and soft landscaping (eg. gardens).

Something seems at odds between the actual built environment and the planning requirements (both past and present). As blocks of land have been getting smaller whilst houses have been getting bigger, and open space in neighbourhoods getting less.

🏠 2025 is going to be a big year for housing in South Australia with many major projects underway or nearing completion.

We recently completed 12 new homes north of the city which were able to be occupied in time for Christmas. They’ve been allocated as public housing for those most in need. We also built a park across the street to give families a great outdoor space to get out and play!

Just down the road, dozens more homes are also nearing completion and will be a combination of public housing and affordable homes for purchase. We look forward to sharing more about them soon.

It’s all part of our Urban Renewal program to build new communities and get South Australians housed faster.

EDIT: Thanks everyone for the lively discussion. Comments on this post are now closed as a moderator is no longer available.

08/01/2025

Not sure I see what the residents problem is. In rural towns, people either have septic tanks and drainage fields, or they are connected to a common effluent system. Planning code minimum allotment area is 1200 sqm for use of a septic system. If smaller area then get connected to a common effluent system, still need septic tank as only gets rid of the liquids. Septic tanks only need emptying every few years.

As far as I can tell these people don't have septic tanks, their houses are designed to be connected to the sewers. The sewers aren't connected directly to the sewage treatment plant, and instead being collected in a local community tank. The tank is being emptied frequently (daily). That may be a problem if the tank isn't large enough and is backing up and not getting emptied fast enough.

Otherwise what is the problem? The tank and treatment works have to be some where. So could connect to existing by laying pipeline and expanding existing sewage treatment plan, which appears to be the proposal. The alternative would be a new sewage treatment plant say a lot closer to their homes, at some point it is going to be impractical to expand the existing further and a new facility will be required.

Lack of other services is understandable as edge of city is now encroaching on what were remote rural towns, and over the decades there has been to much emphasis on Adelaide being the centre of everything. It seems the idea of a satellite city failed, and so haven't put any effort into decentralising and creating more local community centres.

Australia is developing. The original migrants understood they were contributing to a developing country. Population growth is still largely due to migration, and still developing. People haven't been flowing in to fill empty houses and empty jobs. There was deliberate intent to increase population to keep building industry employed. Now housing shortage and shortage of skilled workers in building industry.

But average household occupancy less than 3 people per household, and had potential to drop to 2 people per household by 2015 if no population growth. But it didn't it's still around 2.6. So we've stretched the city beyond its limits and still need more land for more housing, and still pushing immigration.

We don't really need more land rezoned. We really need to use, the land which is already occupied, more efficiently. That is convert the common 3 bedroom family houses and allotments, into two dwellings suitable for 2 people each. So still have a maximum of 4 people per allotment, so no increase load on infrastructure and neighbourhood. But potentially double dwellings and average drops to 1.5 people per dwelling.

In short we shouldn't be expanding outwards, if anything need more 2 storey and 4 storey apartments near schools, shopping centres and hospitals: and property which is rent only. Why knock down old schools and build new schools elsewhere, when we can have people live in the right area at the right time?

Earlier this year the Federal Government announced it would pour billions into building new homes.But for residents in our newest suburbs basic infrastructur...

02/07/2024

The SA Planning Code, the National Construction Code (NCC) and the SA Minimum Housing Standards can be considered as an imposition or a benefit.

One the one hand they may impose a greater level of performance on your house than you desire or can afford, on the other hand they can be used to argue down the price of existing buildings on the basis that they do not comply.

For example the 7.5 sq.m minimum for a bedroom, is largely because houses are sold on the basis of the number of bedrooms. The minimum value allows you to argue that a dwelling, isn't a 3 bedroom house but 2 bedroom with a utility room or storage cupboard.

Or argue that a house lacks energy efficiency. The added verandahs rather than added value are a problem. They cut out sunlight in winter, and reduce solar gain through windows resulting in higher heating costs in winter. Whilst could argue reduces solar gain in summer and reduces cooling costs, in the main only need a 600mm eaves overhang to achieve that, not a 6000mm wide verandah.

There are a multitude of requirements in the NCC which can be used to identify that an older house is of lower performance than current codes require. Whilst there is no requirement to upgrade the house, that doesn't mean that the market has to accept the available rubbish littering the land.

Compared against the planning code can also identify issues such as doesn't have the required volume of storage space, that there is too little private open space, there is a lack of circulation around the building, that too much of the allotment is covered with building.

Treat established, existing buildings as raw material. Then how much time and effort is required to modify and adapt to make it suitable for purpose, compared to putting a bulldozer through it and starting from scratch. So ultimately demonstrate that not interested in the building, just want the land, and will put suitable building on that land.

Now if buildings are constructed from transportable modules, it becomes a lot easier to modify population density in an area. As can easily move modules and whole buildings in and out of an area. Can more easily convert a 3 bedroom house into 2 sole occupancy units, with their own or shared gardens.

29/06/2024

It seems I was partly wrong about not being any minimum dwelling sizes in South Australia. The planning code has performance outcomes (PO 22.1 / PO 31.1), which states:

"Dwellings are of a suitable size to accommodate a layout that is well organised and provides a high standard of amenity for occupants."

Then there are deemed-to-satisfy (DTS) criteria which indicates minimum dimensions for studio, one bedroom, two bedroom and three or more bedrooms. The dimensions being 35 sq.m, 50 sq.m, 65 sq.m, and 80 sq.m, with an additional 15 sq.m for every additional bedroom above 3.

From my previous post the minimum housing standards set minimum of 7.5 sqm for a room to be considered a bedroom. So it may seem unreasonable to be adding an extra 15 sq.m. However, basic functional rooms such as lounge, dining, bathroom, kitchen and laundry may require additional space for each person. So that 5 rooms, so an extra 7.5 sq.m to be distributed between the other rooms, is 1.5 sq.m per room. Assuming about 3m wide, then length of room increased by an extra 0.5m, so space for extra seating in lounge and dining room. Also at a certain point, need extra storage in kitchen, and laundry, and also may need extra bathrooms. So the whole 7.5 sq.m, or large portion of may be used for a ensuite to each additional bedroom.

These limits do mean that 25 sq.m sole occupancy dwelling is too small, as is a 36 sq.m dwelling. A shipping container at 2.4 x 6=14.4 sq.m would definitely be too small. Whilst a 16ft (4876mm) caravan, which can squeeze a bathroom and kitchen into and sleep 4, and assume 2m wide, would have area 9.75 sq.m, and also too small.

However, they are only too small concerning the deemed-to-satisfy criteria. The requirement of "high standard of amenity" is not explicitly defined. But minimum housing standards do set minimum facilities to be provided. Turning a dining area into a bedroom every day may be considered something of an inconvenience and a lack of amenity. As would be turning lounge into a bedroom. And whilst maybe tolerated and acceptable to one person, it may not be acceptable to others and therefore permanently connected to the land is not acceptable. The permanent dwelling needs to be acceptable to as many people as possible within its type.

I'd argue that 25 to 36 sq.m dwelling should be acceptable for a sole occupancy dwelling, if it has a bedroom, and a shared dining/lounge area. Rather than a shared lounge area with a sofa bed. I'd also argue that a dwelling suitable for one is also suitable for a couple.

Based on the 2.5m x 5m (12.5 sq.m) strip modules mentioned in earlier posts, then one additional strip module would improve lounge and dining area., pushing area up to 37.5 sq.m, would seem reasonable for a 1 to 2 person dwelling.

I previously indicated that an extra 2 bedrooms can be provided by adding one extra strip module. But 12.5/2=6.25 sq.m which doesn't meet the minimum size room to be counted as a bedroom. Increasing modules to 2.4x6=14.4 sq.m per module, and provides 7.2 sq.m per room. Whilst 3x6=18 sq.m modules, gives maximum of 9 sq.m per room thus extra for hallways. An increase to 2.7m wide modules, would increase area to 16.2 sq.m per module, and 8.1 sq.m per room.

So issue is to demonstrate that the additional area is waste space.

31/03/2024

Interesting aerial photographs of fringe dwellers, shanty towns and areas of poverty.

One thing is apparent and that is the poverty areas do not have the planning constraints that the other areas have. Part of the origin of modern building codes is a requirement for circulation. One issue was lack of circulation posing problems with fire fighting and spread of fire. The other issue was lack of adequate ventilation and fresh air into the streets and houses.

Building houses closer together reduces travel distances. But could these make shift buildings be spread further apart, placed on individual allotments, and provided with better circulation around the buildings and provide more private open space to the people.

That is grant licence to occupy and use the land, and subdivide the areas occupied into small allotments. Providing at least 1.2m corridor around each building. This would require more land than currently occupied, but would make the occupation less of a hazard for all.

One photographer's incredible drone images capture the stark reality of cities where rich and poor live side by side

31/03/2024

Rental Crisis in Australia and around the world. Shows comparison with Sydney, New York, London, Tokyo.

Rental costs are soaring, but not just in Australia. Our reporters are criss-crossing the globe to find out what’s going on. Armed with 30% of the median hou...

31/03/2024

Here's another perspective view on global fertility rates and potential declining population. That is the places currently with high fertility rates are expected that they will also eventually decline.

Starting in the 20th century, the fertility rates of the world went crashing down. In just one or two generations nations went from 7 or 8 babies per woman o...