Construction systems

The combination of materials used to build the main elements of our homes — roof, walls, and floor — are referred to as construction systems. These materials are many and varied, and each has advantages and disadvantages depending on climate, distance from source of supply, budget, maintenance requirements and desired style or appearance.

Give careful consideration to your choice of construction system early in the project. Changing systems late in the design or construction process can be costly, particularly if the change requires structural alterations.

New homes in Australia are often built in standard ways. It is worthwhile thinking about how the construction system will suit your climate, and how much environmental impact it will have.

Types of systems

A building can either be constructed entirely on site, or constructed in modules off site and assembled on site.

On-site construction

An on-site built home is the traditional method of constructing new homes. The home is built on the site starting from the foundations and finishing with the roof. All the raw materials and supplies are brought to the site, unloaded and installed as they are needed.

On-site construction provides greater flexibility in design, but can be slower, especially if there are weather delays.

Modular construction systems

With modular construction, most of the work is completed off site in a factory environment. There are two different approaches to modular construction:

• ‘Flat pack’ or component modular construction – large components of the house are prefabricated to varying stages of completeness in a factory, and stacked for transport on a truck. The components are then assembled on site.
• ‘Big box’ or volumetric modular construction – whole and complete components are taken to site by truck, and joined up to make the whole building. This is the most common system and demands the least amount of time on site. Foundations are prepared, water and sewer connections made, and then the boxes are craned into position, with minor detailing to the joints carried out over a matter of days.

Source: Prebuilt. Photo: Michael Kai

Modular or prefabrication construction has several advantages over on-site construction. The building or components are fabricated in a controlled factory environment which is cleaner, faster, with no weather interruptions or damage, and results in less material wastage.

However, consideration is needed for site access and maximum module width. Most modular builders have detailed maps that allow them to quickly determine the maximum module size, and all design work must be based on this parameter. Crane access and overhead wires are the next major consideration.

Source: Prebuilt. Photography: Dan Hocking

Thermal performance of construction systems

One of the key differences between various construction systems is their mass content. High- and low-mass materials contribute differently to thermal performance depending on the climate zone they are used in and how they are designed to interact with or moderate the climate.

In temperate and cold climates, high-mass construction can contribute to thermal comfort by absorbing solar heat during the day and releasing it at night or on cloudy days. For this passive warming to happen, passive design principles must be used to ensure the mass is exposed internally and insulated externally. In hot and humid climates, low-mass construction works better to encourage passive cooling.

High-mass systems

Such systems:

• can reduce heating and cooling energy use
• are most appropriate in climates with high diurnal (day–night) temperature ranges
• can be a liability in tropical climates where energy is used only for cooling
• generally have higher embodied energy
• require more substantial footing systems and cause greater site impact and disturbance
• are often quarried and processed with high environmental impact
• require careful cost–benefit analysis on remote sites where transport needs are significant.

Lightweight systems

Such systems:

• respond rapidly to external temperature changes or heating and cooling input
• can provide significant benefits in temperate and hot climates by cooling rapidly at night
• may require more heating and cooling energy in high diurnal range climates
• generally have lower embodied energy
• are often preferable on remote sites with high materials transport cost
• can have thermal mass added through inclusion of water-filled containers or phase-change materials
• can have lower production impact if sustainably sourced.

Mixed mass systems

In most areas of Australia, a well-designed combination of low- and high-mass construction produces the best overall economic and environmental outcomes.

In temperate climates, the best overall outcome is most simply achieved with concrete slab-on-ground and lightweight walls. In hot humid climates, low-mass construction is preferable. In cool climates, high mass is desirable. In cold and hot arid climates, careful positioning of low and high mass throughout the building is required to achieve the best outcomes (refer to Design for climate).

Photo: Steve Wray and DSEWPaC

Construction system elements

Different construction options are available for all parts of your home.

Footing systems

Footings are the base of your home. They are the structures that transfer the weight of the home to the foundation material, most commonly soil.

Footing systems must be designed to suit the site’s soil conditions and provide adequate tie-down for the building structure under the site’s wind classification. A good system also minimises site disturbance and uses low quantities of materials that have high embodied energy, such as concrete and steel.

Footing system options include:

• Lightweight framed systems – These have the lowest site impact and embodied energy. A broad range of lightweight steel footing systems is available including screw piles, adjustable steel piers on a simple concrete pad or bored columns, and pole and space frame systems.
• Concrete slab integrated footings – These require substantial excavation on all but level sites, increasing impact. They can reduce construction costs where the slope is low. They can be an effective part of passive design where the climate allows for earth coupling.
• Waffle pod slabs – These can be a cost-effective solution on flat sites and they don’t require major excavation. Waffle pods reduce the overall cost of the slab because they create a ‘void’, which uses less concrete and reduces the cost of labour. This means they also reduce wastage and have lower embodied energy than a typical concrete slab.
• Detached strip footings – These, combined with loadbearing brickwork to floor level, can reduce excavation.
• Engineered steel pile systems – These can support masonry walls, reduce excavation and site impact, and make for faster construction. Cost varies with application but these systems are generally more expensive than strip footings.

Photo: Light House Architecture and Science

Floor systems

High-mass floors

High-mass floor system options include:

• Concrete slab-on-ground – This is the most common high-mass floor system. In cold climates, insulating under the slab will reduce heat loss to the ground; in permanently hot climates, insulating under the slab will prevent heat entering the home. If the slab is not insulated, the summer cooling benefit of earth coupling may or may not exceed the additional energy required in winter to compensate for the uninsulated slab on ground. Earth-coupled (uninsulated) slabs are effective where deep (>3m) earth temperatures remain constantly between 16°C and 19°C.
• Suspended slabs or precast concrete beams – These can be used with lightweight infill and concrete topping. To contribute positively to thermal performance, the underside of suspended floors, including subfloor spaces, must be insulated if externally exposed.
• Lightweight suspended concrete floor systems – (such as autoclaved aerated concrete (AAC) floor panels, or thin poured concrete slabs on permanent formwork, supported on floor joists). These may be competitive in cost with conventional timber- and steel-framed floors, and can reduce site impacts where a slab floor is preferable to a lightweight floor. The underside of thin concrete slabs must be insulated; AAC provides sufficient insulation on its own in many climate zones.
• Compacted earth, flagstone or rock – This is less common (for example, occurring in Coober Pedy in central Australia) but is effective when properly designed and built for climate and site (refer to Thermal mass). Such systems have either low or no embodied energy and minimal transport impact.

Low-mass floors

Low-mass floor system options include:

• Lightweight steel framing – This has higher embodied energy than timber but is highly recyclable. Steel framing has greater durability in termite-prone areas and often has lower transport costs than equivalent timber structures. It is subject to rust in corrosive environments; galvanising can eliminate this but adds to embodied energy. It is usually more expensive than timber once subsequent fixing costs are included. Steel framing must be appropriately insulated or it will act as a thermal bridge, increasing the risk of condensation.
• Lightweight timber framing – This has low embodied energy and is a carbon sink. Sustainably sourced plantation timber should be used. When designed and built for deconstruction (for example, screwed, not glued), this flooring has a high potential for reuse at the end of its life. Timber is subject to termite attack and, while termite proofing reduces this risk, nonphysical barriers rely on chemical treatments that have other environmental implications. It is relatively low cost.
• Cross-laminated timber (CLT) – This is built in a similar way to plywood: 15–25mm thick layers of timber are laid with alternate layers at 90° to each other, forming panels from 90mm to 300mm thick. These can be used for floors, walls and roof structure, but always require weather protection and waterproofing. They are more commonly used in medium-density and high-rise buildings. These thick softwood panels have a small but useful insulation value. They will still require additional insulation on external walls, roofs and floors in all climate zones.
• Engineered composite panel or structural insulated panel (SIP) – These systems are growing in popularity. Low-mass insulation materials are bonded to lightweight steel, plywood or oriented strand board (OSB) sheeting and usually achieve high levels of structural efficiency with high insulation levels. Cost ranges from medium to high, depending on the system.

Composite mass floors

Common examples of composite mass floors are:

• lightweight frames topped with concrete
• lightweight systems with water filled inserts to provide thermal mass
• autoclaved aerated concrete (AAC) floor systems
• phase-change materials embedded in low-mass materials to produce lightweight flooring with high thermal storage capacity.

Wall systems

High-mass walls

Common high-mass wall systems are masonry and include brick, concrete block and precast concrete. Other popular systems include rammed earth and mud brick.

Traditional masonry systems generally have high embodied energy while rammed earth and mud brick have significantly less. Rammed earth uses varying levels of cement depending on earth type and therefore has higher embodied energy than mud brick.

All high-mass wall systems must be insulated, and provide most thermal performance benefit when insulated externally and exposed internally.

High-mass wall system options include:

• Double brick – These have high thermal mass and high embodied energy. They require cavity insulation. They are low maintenance (if unpainted) and highly durable on stable soil types. At the end of their lifespan they can be reused if lime mortar (which cleans easily) has been used. Less ideal is the use of high-cement mortar, as the bricks after use can only be crushed and recycled as decorative gravel or road base. They are usually high cost.
• Reverse brick veneer – This wall system has high thermal mass and good thermal performance if coupled with effective external insulation. The embodied energy depends on the materials used: clay brick walls have higher embodied energy than concrete block walls. Clay brick walls are very durable and require little maintenance for the internal surface. The external maintenance depends on the cladding system selected, which can be fibre cement, plywood, sustainably sourced timber or corrugated steel sheets (for example, Colorbond). The cost varies from average to high, depending on mass type and cladding.

   

  Reverse recycled brick veneer with steel external cladding

  Photo: Warren Reed (© Beaumont Building Design)

• Insulated concrete (tilt-up or precast) – These have high embodied energy and high thermal mass, and high insulation values are possible. As with reverse brick veneer, they have low maintenance required for the internal surface, and the external maintenance depends on the cladding system selected; painted finishes will require higher maintenance, whereas off-form finishes are extremely low maintenance. Insulated concrete is extremely robust, and can be relocated and reused. Both types of insulated concrete have good acoustic performance. Insulated concrete walls have low construction times but are high cost.
  

  

  Precast concrete walls being lowered into excavation before waterproofing and earth-berm backfill.

   

• Earth-bermed – These wall systems have the highest thermal mass, and also have the additional benefits of earth coupling, resulting in significantly reduced energy requirements. Insulation is not required in locations where earth temperatures are favourable. They have high embodied energy (assuming precast concrete or reinforced block walls are used). Earth-bermed homes are extremely durable but need very good robust waterproofing. They have high site impact during construction. They are high cost.
• Rammed earth – These wall systems have high thermal mass and low to medium embodied energy, depending on cement content (if used). Insulation can be difficult to add unless lined externally or with insulation integrated within the rammed earth itself. The process has average to high site impact, depending on the footing system, but has minimal manufacturing impact and transport energy. Rammed earth homes are very durable but require periodic reapplication of external waterproofing. Their cost is high.

Photo: Justin O'Connor

Low-mass walls

The most common form of low-mass wall construction uses lightweight timber or steel framing as the structural support system for non-structural cladding and linings such as timber weatherboard, fibre cement, plywood and steel. Insulated lightweight walls reduce heat loss and can have minimal embodied energy, depending on the cladding material used.

Low-mass walls have low embodied energy and generally low environmental impact. They are very durable — although maintenance is required for any painted surface.

Low-mass wall system options include:

• Lightweight using timber weatherboard, fibre cement sheet, plywood and other sheet cladding systems have low thermal mass, but medium to high insulation values can be easily added. Lightweight cladding systems have low to medium embodied energy. They are high maintenance unless protected from weather and termites. They are suited to both off-site and on-site fabrication and have relatively low transport costs. They are low cost.
  
  Lightweight timber framing

  Photo: Hyne

• Cross-laminated timber (CLT) panels – Refer to Low-mass floors earlier on this page.
• Structural insulated panels (SIP) – These consist of an insulating layer of rigid insulation material, sandwiched between 2 structural skins of sheet metal, plywood, fibre cement, or engineered timber. These systems usually achieve high levels of structural efficiency with high insulation levels. Many people now use environmentally preferred materials and the range of SIP products is growing rapidly. Some Australian SIP systems use panels made from forestry waste through a carbon zero manufacturing process. SIP systems can be particularly effective in passive design homes, because they position the thermal mass where it is most useful. SIPs with cores made from non-damaging materials are preferred. There are some small-scale commercial providers using organic materials of various kinds, and others using XPS or PIR foams, both of which are preferable to EPS foam.
  
  This SIP uses panels made from forestry waste and a foam core

   

• Log walls – Low-mass systems include log wall construction. These may achieve good thermal performance with the addition of insulation, and have low environmental impact when logs are sustainably sourced. Construction detailing and timber stability are critical to retain airtightness and thermal performance. Single skin log walls are unsatisfactory.
• Cladding – Lightweight walls reduce heat loss when insulated and can have minimal embodied energy, depending on the cladding material used. Timber weatherboards, fibre cement sheet, and other cladding systems made from compressed forestry waste have low embodied energy and generally low environmental impact. They are very durable, although maintenance is required for any painted surface.

Composite (mixed) mass walls

These systems fit between high and low mass with either moderate density, such as AAC (see following) where high-mass concrete is used to trap tiny (no mass) air bubbles, or a combination of high and low mass, such as straw bale, where straw is low mass and the render finish is high mass.

• AAC (Autoclaved aerated concrete) panels – These panels have medium thermal mass and insulation, and low to medium embodied energy. The maintenance required depends on the finish. AAC panels have average durability (depending on finishes). These panels are also prone to damage if not handled with care on site. They have low processing impacts and moderate transport requirements.
  

  

  Autoclaved aerated concrete (AAC) contains closed air pockets that make it lightweight.

  Photo: Maxiwall (© Big River Group)

• Concrete block – These have good thermal mass when filled with concrete, but low insulation values (which is difficult to add unless lined externally). They have lower embodied energy than concrete or brick because they are hollow and contain less concrete per square metre. However, when filled with concrete they can equal or exceed the embodied energy of brick. Fly ash blocks further reduce embodied energy. They are not easily recycled because they have insufficient strength for reuse, but they can be crushed as gravel or fill. They are average cost.
  
  Concrete blocks have low insulation but good thermal mass.

  Photo: Getty Images

• Mud brick (adobe) – These have high thermal mass, but insulation is difficult to add unless the walls are constructed with a cavity, or are lined externally. They have the lowest embodied energy (if sourced locally) and no manufacturing impact. They also have low site impact and are suited to remote sites. Mud brick homes will require regular waterproofing in exposed locations. They are low cost if labour is not included (owner built).
  
  A mud brick is pressed using a mould.

  Photo: Getty Images

• Straw bale – These have low to medium thermal mass (depending on render thickness) and excellent thermal performance. They have low embodied energy (some additional embodied energy and materials in extra width footings and slabs). They have excellent breathability when rendered with earth- or lime-based renders. However, long-term durability will depend upon build quality – straw bales must be compressed well to minimise settlement and movement, and generous overhangs are the most reliable rain protection. Maintenance levels are variable depending on the finish. Cost varies from average to high.
• Panel systems – Sandwich panels have varying embodied energy depending on surface materials and insulation. Other lightweight panel systems, such as straw board and recycled paper products, have low thermal mass, high insulation levels and very low embodied energy. They respond rapidly to heating and cooling and are ideally used with a high-mass concrete slab floor. The recycled content of many commonly available systems is high. The reuse potential is good, waste rates are low and transport costs are low. Construction cost varies from high to average.
• Hemp lime composite (hempcrete) – This building material is composed of hemp, lime binder and water. It offers a range of ecological benefits and provides good insulation and excellent permeability to water vapour.

Roof systems

High-mass roof systems

Roof systems are usually low mass. This is because thermal mass cannot improve thermal performance unless it is exposed internally, and exposed roof mass is unusual except in multilevel homes or apartments.

Where high-mass systems are used, they are usually part of an overall building system. High-mass roof system options include:

• Earth-covered construction – When carefully designed, these systems can provide sufficient thermal lag to moderate seasonal cycles, so that summer earth temperatures reach the exposed ceiling mass in winter and vice versa. These homes require no maintenance for the roof and are very durable. Care must be taken to waterproof the home correctly. They have high site disturbance during construction, but minimal on completion. They have high embodied energy and are high cost. Earth-covered construction also eliminates roof area, so any rainwater collection is limited to out-buildings.
  
  Earth-covered construction can provide sufficient thermal lag to moderate seasonal cycles

  Photo: © Peter Hughes Photography

• Green roofs – Rather than earth, these use a lightweight manufactured material as a medium to grow plants. Thermal mass is generally inaccessible due to the structure, and insulation is medium to high and provided by conventional insulation rather than the covering. They have medium to high embodied energy, depending on support structures. Other environmental benefits include food production, increased ecological habitat and biodiversity, reduction of heat island over built-up areas, air quality improvement and on-site stormwater detention. They are low to medium maintenance, depending on the plants grown.

Low-mass roof systems

Low-mass roof system options include:

• Tiles – Concrete tiles have slightly lower embodied energy than terracotta. They require more structural support than lightweight materials and can add to heat gain unless well insulated, because they are external, uninsulated thermal mass. While recycling and reuse rates are improving, this is still lower than other materials. Some manufacturers claim up to 40% recycled content in concrete tiles. High transport costs make them inappropriate for remote sites.
• Metal sheeting – This has high embodied energy per kilogram, but because it is thin, the embodied energy is low per square metre. Metal roofs with high performance pre-bonded baked enamel coatings are very durable, easy to transport to remote sites, and available in light colours and reflective finishes to reduce heat gain in summer. Sheeting may have recycled content (check with the manufacturer) and end of life recycling or reuse rates are high.
• Structural insulated panels (SIPs) – These typically are made with 2 skins of pre-coated thin steel 0.42mm thick with the profile rolled for added rigidity. The metal is glued to a rigid foam core, preferably either XPS or PIR rather than EPS. The thickness can be varied to give very high insulation values. They are an efficient use of the embodied energy in steel as they have very high performance and longevity. The cost per square metre is higher to purchase, but the speed of construction dramatically reduces site labour costs.

Important factors influencing the selection of residential construction systems are:

• thermal performance
• durability and maintenance requirements
• source and environmental impact of all component materials and processes
• reuse or recycling potential
• distances and transport modes required for materials and labour.

There is no single best solution. Any combination of materials should be carefully assessed to arrive at the most appropriate choice for your climate and site.

Thermal mass

• Choose the right thermal mass and passive design for your climate.
• Pay attention to lifecycle energy consumption – a material’s environmental emissions and depletions from ‘cradle to grave’– for example; source, extraction, manufacture, operating performance and end of life disposal or reuse.
• Balance higher embodied energy with lower energy use as appropriate (for example, heavyweight construction may outweigh operational energy savings).

Durability and maintenance

• Make sure the materials you choose have a durability of at least the lifespan of the building.
• The durability of well-maintained lightweight systems is equivalent to heavyweight systems.
• Also make sure that you can perform the upkeep required to maintain any of the materials. Reliable maintenance regimes are a critical consideration when selecting external cladding systems.
• Painted surfaces will require more maintenance than unpainted surfaces.
• Poor maintenance can reduce life span by up to 50%, negating embodied energy savings and doubling materials consumption.

Source and reuse of materials

Choose materials that are:

• lifecycle certified by an accredited scheme (for example, Good Environmental Choice Australia, Global GreenTag, EcoSpecifier Global)
• renewable, in preference to those from finite resources
• low in embodied energy, unless that will be balanced by operating energy savings
• certified as not threatening to biodiversity
• low toxicity in both production and operation
• high in renewable or recycled content (for example, fibre cement cladding, sustainably managed forest timber frames or recycled plastic/sawdust decking), as long as the durability and performance are appropriate.

Design for:

• structural efficiency to minimise overall material use, waste, transport and processing
• deconstruction, recycling and reuse
• construction systems with known low wastage rates and environmentally sound production processes.

Transportation

• Use locally made products where possible to reduce transportation.
• In remote areas, avoid systems with a high on-site labour component to reduce travelling.

Site-specific considerations

Other considerations that may be relevant to your site include:

• specific site requirements such as slope, stormwater, sediment control, biodiversity impact, noise control and fire resistance
• regulatory and planning issues
• exposure to natural hazards such as fire, termites, storms, UV and humidity.

• Eco-comparison websites
  –    Australian National Life Cycle Inventory Database
  –    Building Products Information Rating
  –    Ecospecifier Global
  –    Environmental Product Declaration Australasia
  –    Global GreenTag
  –    Good Environmental Choice Australia
• Carre A (2011). A comparative life cycle assessment of alternative constructions of a typical Australian house design [PDF]. Report for Forest and Wood Products Australia prepared by RMIT Centre for Design, Melbourne.
• Crawford RH (2019). Embodied energy of common construction assemblies (Version 1.0). The University of Melbourne, Melbourne.
• Department of Industry, Science, Energy and Resources (2020). Residential energy baseline study: Australia 2000–2030. Australian Government, Canberra.  
• Lawson B (1996). Building materials, energy and the environment: towards ecologically sustainable development. Royal Australian Institute of Architects, Canberra.

Learn more

• Read Embodied energy to understand the energy used in your building materials
• Refer to Waste minimisation for more ideas on how to reduce the use of building materials
• Explore Design for climate to discover which designs will suit your climate

Authors

Original author: Chris Reardon

Contributing author: Paul Downton

Updated: Chris Reardon 2013, Dick Clarke and Andy Marlow 2020