Plateau - Unconventional building techniques.

Sydney area proposals

The conventional architect-designed techniques and sequences of construction are not necessarily either required or desired with Plateau development. Nor do all the normal environmental requirements and/or financial objections necessarily pertain. This is not conventional start-to-finished building development program. The plateau itself would be progressively constructed, and this may possibly be over many years.

It is important to realise that:

  1. Excavations: It is intended to excavate as little as possible of the ground surface before the deck is constructed. The aim is to avoid as much excavation as is possible.
    • Any unpredicted need for drainage and sewerage trenching can be done after the deck has been laid since it is still accessible under the plateau.
    • To help maintain the slow-steady development, the aim would be to keep the under-deck area operating as a car-park for general use for as long as necessary.
    • The most obvious predictable-need for excavations is that of perhaps promoting the construction of a multi-layer underground car park (say) on a railway easement adjacent to the railway station. This should be a State government development, and in Sydney's sandstone country, this is not a major problem or a major cost (underground car parks don't need walls, outside facades, interior finishes, etc.). In Sydney the railway car-park can earn revenue for the State transport authorities via the Opal card.

  2. The deck itself:
    • The suggestion is to construct the deck over the existing transport corridors by using Hollowcrete precast tension-reinforced concrete planking, which can be cut to size and craned into place during normal pauses in the road and rail traffic.
    • This deck above the potentially noisy transport corridors would be reserved for a central low-rise shopping/mall space for cafes, restaurants, small shops and professional service suites (Two floors only).
    • Such a business centre would be a highly desirable location for the local professionals and shop owners since their CBD custom is no longer bisected by traffic corridors and easily accessible to everyone (via some lifts from the car parks).
    • The main concrete deck for residential use, over the old 'commons' car park, would probably be conventional poured suspended concrete. This area would be reserved for small home construction (probably of modified Victorian terrace houses). This deck would not necessarily support the modified terrace house blocks itself, but it would abut and surround them. The house units themselves would be built in the conventional foundations, probably using concrete block walls and either timber or concrete floors (with almost flat corrugated gal-iron roofing and solar panels).

  3. The strength of Hollowcrete over traffic corridors:
    • Hollowcrete precast tension-reinforced concrete planking is a relatively new construction technique, with the prestressed panels being made by a couple of different companies. We only suggest this product because it solves the problem of decking over highways and railways in non-disruptive ways. Hollowcrete is strong enough to support the loads on warehouse floors and it can be supplied cut to size and craned into place during normal pauses in the road and rail traffic. [see the illustrations below.]


    From our experience; the initial knee-jerk reactions to the use of a concrete deck to create a new raised "ground level" with footpaths and small garden beds, raises many objections because of the unconventional approach. The main objections are:

    • Q. This must be an expensive way to build small houses.

      A. In fact, since it repurposes the air-space over transport corridors and parking areas, and the land title remaining with the local-councils and state transport departments, this creates the cheapest possible home-building area in the centre of the business district.
        [Note: Old homes in Lindfield at a distance of 1 kilometre from the CBD and transport hub are regularly being sold, demolished, and rebuilt. The land cost is currently $1,800 per sq.m, while the concrete slab costs is a fraction of this.]

    • Q. How small are the small homes?

      A. The plan is to create pillars under the deck with (generally) 4.2m separation, which gives space for two-cars to be parked, and provide a supporting module-size and a good, but economic room dimension (but this isn't a total requirement).
        We would suggest therefore that the ground floor unit for an elderly member or couple (and for the units above and below this), would require 1 module (4.2m) of width, with a living-room kitchenette length of 1 module; a corridor, bathroom and small visitor's bedroom sharing another module; and a third module (full length and width) for a large bedroom/sun-room space at the rear.
        Also each unit would occupy another module of space for a garden over the shared car-park, and have across the front a common 3-metre wide verandah used both for access and as a community casual area. This leaves space for a light-well if there is a basement flat.
        The top-level and basement flats can follow the same pattern which means that a single "terrace" unit with three separate residences, uses a deck-space of under 100 sq.m (21x4.2 - plus some footpath and turfed areas in front). Allowing for under-deck car parking, this is a household occupancy amplification of around 18x to 20x over normal suburban dwellings.

    • Q. How flat and level can the deck be, since the underlying land is not being contoured?

      A. The aim is not to create a billiard-table flat deck, but a contoured turfed/garden and footpath surface around the main elderly housing units. This "new ground surface" should have gentle slopes for rainfall run off, and provide:

      • moderate exercise for aged pedestrians,
      • easily sloping foot paths, navigable by gophers and electric wheelchairs
      • no need for road crossings.
      The rain should drain via the rock-rubble in the under-turf layer. Water can be harvested and stored at the lowest point, then solar-pumped for toilet flushing and garden use.

      If the deck has one side down a hill, we would use two under-deck levels, which can provide exercise and woodworking spaces, storage area, or (depending on window access) be used for a nursing home, etc.

    • Q. What about the energy being used in the manufacture of all that concrete?

      A. Environmentalists and climate activist have objected to the use of large concrete decks on the grounds that the manufacture is costly in terms of carbon dioxide generation. In fact, this construction technique provides the whole plateau area with very substantial daily energy savings, in both hot and cold weather:

        a. Energy consumption is offset by the sheer thermal mass ... the ability of concrete with a turf-cover to store and absorb heat and therefore maintain a relatively stable temperature.
        b) earth-coupling over a wide area. In effect, the large size of cavity compared to the outside wall area, brings the thermal mass of the earth into play to a very large degree (cave-like conditions).
        c) the use of natural insulation via soil and turf covering maintains temperature within the under-floor of the plateau, and allows simple turf-water sprays on the deck level to cut heat by evaporation.
        d) Heat in winter is exchanged between areas horizontally.
        e) reduced heat leaks (out and in) through exterior walls; the ratio of cavity size outside walls is extremely favourable.
        f) low future maintenance costs. You don't waste the energy which goes into the construction by the need to rebuild a decade or so later.
        g) the ability to treat the under-Plateau cavity as multiple "passive" divisions for requirements of both temperature and humidity without expensive air-conditioning systems. This ability to divide and seperate also has significance for virus control.
        h) The whole design is focussed on placing less dependence by the occupants on cars and fossil fuel.

        Note that this is an ideal housing development style for a reasonably large-scale solar-generation system and battery installation. The plateau could easily be self-sufficient in total energy terms.

    • Q. What about the potential dangers of an under-deck gas explosion?

      A. The potential dangers of a gas explosion in the under-deck space has been discussed following the Lebanon catastrophe. We believe that gas should therefore be prohibited as an energy source in the plateau area. It is probably unnecessary anyway.

    • Q. How would you plant gardens and maintain trees on a concrete decak?

      A. Nature lovers have pointed out the difficulties of maintaining and planting gardens (particularly large trees) on such a concrete decked site. They have also queried the aesthetics and the attractiveness of the area to wild-life.

      The elderly have problems maintaining conventional ground-level gardens, so the use of raised flower beds (using a few rows of wooden sleepers) will provide both seats and workable gardens space for the enthusiasts.

      With existing trees, the aim would be to leave most of them in place and deck around them (creating air & light atriums). This may only be a temporary measure, but the value of the plateau approach is that change can be progressive, and change can be easily managed. New trees can be planted in large concrete pipes which also serve as column supports for the deck.

    Plateau Group Convenor: Stewart Fist
    Click here to email


Some Hollowcore images: deck planks used for warehouses, (heavy duty) and made by many companies.

There has been some doubt thrown onto the ability to use these materials over the transport corridors. They are manufactured to specification, so they are not cheap, but they solve a problem and consequently the financial benefits are in cheap building and usage areas created. Note the span in the warehouse complex on the right (Scale - note figure of man)