The Bones of Modular Construction: Benefits and Challenges of 3 ...

Wood, steel, and concrete: Each has been used in various forms of traditional construction for centuries (with steel being the most recent addition), and each provides specific benefits and challenges to consider. In a nutshell, wood is light and moderately strong, ideal for small and medium-sized buildings. Steel is heavier but stronger and perfect for taller, more complex frameworks. Concrete is the heaviest and is best suited for foundations and reinforced structures.

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Each of these materials has its use in modular construction, as well. The modular construction process, however, allows for a slightly different set of benefits and challenges, and the design of the modular project can determine which materials need to be used during construction.

Below, we break open the nutshell and explore each material’s use in modular construction.

Modular Construction with Wood

According to Allison Arieff & Bryan Burkhart, the authors of the book “Prefab”, use of wood in modular construction is the most common practice since the seventeenth century. Using wood in modular construction is very beneficial due to its properties as a construction material. Wood is easy to manipulate by hand or with machinery, has low toxicity, is biodegradable, is easy to reuse and recycle, and is affordable. Wood is a combustible material that has an important thermal property in that it does not expand against heat. In fact, it gains strength when it dries out with more heat. Wood is also a good insulator against electricity (helps to minimize electrical shocks) and energy loss.

Common structural members used include 2X individual pieces used in roof trusses, floor trusses, walls; wood I-joists, engineered glue-laminated beams, plywood, oriented strand board (OSB) and composite panels. Wood is being used in the modular fabrication shop to create exterior wall panels that include additional layers for waterproofing, insulation, vapor barrier, drywall and siding.

Prefabrication in a factory allows the wood to stay dry and at a constant temperature while being precisely cut and fitted to exacting tolerances. Prefabrication minimizes waste, saves resources, and simplifies recycling of waste. Factory-produced components or modules can be transported to the site and assembled with extremely tight tolerances. With its ability to be manipulated, laminated and reused, wood will continue to be a sustainable material source for modular construction.

Modular Construction with Steel/Aluminum

Metals can be described as ductile, hard, conductive, precise, and strong. They are classified as ferrous and non-ferrous metals. Ferrous metals are primarily used in structural applications because they are strong, ductile and durable due to their high iron content. They can be treated with coatings such as galvanizing to prevent corrosion when exposed to weather and manipulated easily to create a variety of shapes and sizes. Non-ferrous are used in roofing and cladding applications and are natural corrosion-resistant metals.

Although steel is an expensive material when compared to wood and concrete, steel is the more economical choice if building long-span structures, high-rise structures and unique geometric designs because of its strength and speed of construction. Steel is inorganic and non-combustible material, therefore it has an advantage against fire. Another advantage of steel structures is that they are very strong and can survive even in the most critical weather conditions. It can be used for a long time due to its strength and durability. It can be transported easily and can be reused by unbolting its components.

Aluminum is a non-ferrous alloy that is ductile and well-known for its corrosion-resistance. It can be recycled repeatedly with little energy or loss of its material properties. Because aluminum is light and durable, it can be easily assembled into panels and modules, shipped and erected quickly and accurately.

Light-gauge steel components (which have a higher strength-to weight ratio) can be used in place of 2X lumber or in tandem with wood framing. For studs and rafters, members are formed into C-shaped sections. For top and bottom wall plates and joist headers, channel sections are used. Holes are placed in them every two feet to accommodate wiring and plumbing.

Modular Construction with Concrete

Traditional onsite construction involves concrete that is mixed from Portland cement, sand, aggregate (small gravel of various sizes) and water in a process called hydration which hardens (cures) the concrete to its specified strength (i.e., psi). Concrete relies on fiber and steel reinforcing for its tensile strength. The material is labor intensive because formwork must be erected, concrete placed (poured into the formwork), and then finished (troweled and smoothed).

Modular construction with concrete typically consists of buildings such as restrooms, concession buildings, shower facilities, shelters, utility buildings, etc. in which the walls are fabricated with high strength precast concrete or concrete masonry units (CMUs) and the roof can be constructed of lightweight precast concrete panels, metal panels, concrete tiles, or traditional architectural shingles. The buildings are designed and constructed to meet all local building codes. They can have a variety of color and texture options such as brick, stone, stucco, split-face block, board and bat siding, or horizontal lap siding. The buildings are prefabricated and delivered complete and ready-to-use, including plumbing and electrical where applicable. Modular concrete buildings can also be constructed on permanent, poured-in-place reinforced concrete foundations. These buildings are permanently anchored to a massive foundation with a deep footing designed for heavy seismic loads to ensure stability and integrity of the entire structure.

 1. Greater Efficiency

Using steel for modular construction saves time and money.

Manufacturers can order steel construction components from suppliers to the exact size and specifications in the CAD drawings. This results in a streamlined installation process.

Depending on the size and complexity of the building, the subframe can be put together in a matter of days. Plates and gussets are customised to the precise length required, including holes for connections. By lifting a steel subframe from the top of the structure, you can reduce installation time and improve site safety.

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Light gauge steel wall frames are supplied in pre-rolled sections. The frames arrive braced and perfectly straight, meaning that walls can be installed with minimal fuss. Unlike timber frames, no additional preparation is required before plastering.

The average time it takes complete a basic frame for 5 modules is a week. Shorter construction and installation times mean there are lower holding costs on site and greater rental yields.

There are whole of life cost savings too. Steel is inherently more durable, has greater corrosion resistance in harsh environments and is impervious to termites and wood rot. Steel also has the advantage of being easy to alter should the building need to be extended or renovated during its lifetime. Steel framed modular buildings that are over 30 years old can be stripped back to the steel frame and refurbished with modern building materials and technology to give it a fresh lease on life.

2. Design

One of the common criticisms of early modular construction is that the buildings look like boxes. Steel’s durability, strength and malleability helps designers to challenge this preconception. Designers using a steel frame can create effects like cantilevered modules, curved features and pitched roofs. These features generate more visual interest and can disguise the building’s modular construction method.

The strength of steel enables designers to use larger open spans that have a more contemporary, open design across building modules. Not just appealing to look at, these spaces are particularly important in the education sector, where open plan learning is greatly valued.

The strength of steel means that it can be used on difficult sites with steep gradients. It can also support modern multi-storey modular buildings. In Croydon, Greystar is building the world’s tallest modular building, 101 Georges Street. This residential tower will be 135 metres high, and 44 storeys.

3. Safety

For building occupants, steel is a safer option compared to traditional timber. Steel has a much higher level of fire resistance and is integrated into a building design as a fully engineered system that can be easily verified. Welded connections are inherently stronger than timber connections and welded joins can be easily inspected and verified using non-destructive testing. At the end of the day, clients can expect a building with true structural integrity.

4. Quality

There can be no doubt that using steel ensures a quality result.

All steel is manufactured to a high tolerance of straightness and a high level of dimensional accuracy. These features are traceable and certified by most reputable manufacturers and suppliers.

The durability of steel ensures that all components used in the manufacture of modular buildings will not fail during the transit and installation phase of construction.

Steel is inherently resistant to corrosion. Its performance in both internal and external construction environments is both predictable and assured. This removes any uncertainty about the building’s performance throughout its life. In highly corrosive environments, steel can be protected by hot-dip galvanizing or the application of other suitable coatings.

Welded steel connections are not only stronger than other materials, but they are also very easily tested for verification to the engineered designs and specifications. Bolted connects used in steel fabrications are designed to guarantee their strength and suitability for any application in modular construction. Bolts and fasteners purchased from reputable suppliers will have quality assurance systems that support their manufacture and certify their performance when used as specified.

5. Sustainability

Steel is not just great for the industry, it’s a practical choice for the environment too. Modular buildings constructed from steel are manufactured with a high level of accuracy. As a result, there is very little wasted material during the construction phase and landfill is greatly reduced.

Steel is also 100% recyclable. At the end of the building’s life, all steel components can be removed and recycled for use in other steel constructions or fabrications.

Impact to the environment is minimal. Given the pre-fabricated nature of steel in modular buildings, there are no risks to local areas from dust, spills, pollution, excessive noise or disturbance.

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