HOW HIGH CAN WE GO?

Earlier this year, 461 Dean Street was completed in Brooklyn, New York. At 32 storeys, it was touted as the world’s tallest modular building. Other buildings have also made this claim, such as the UK’s Wolverhampton Building, a 25 storey student dormitory made up of 805 modules. In fact, a quick scan of the global design and construction blogosphere will furnish a reasonable fistful of ‘tallest modular’ firsts.

The speed with which ‘offsite high-rises’ are sprouting across the world can’t yet be described as a gallop, but it is gathering momentum and it is gaining attention. Little wonder, as cities continue to grow, driving demand for relatively cost-effective commercial or residential developments that must be built with increasingly costly resources and labour.

Many in the industry are viewing the growth of the prefab high rise category with cautious optimism, while also learning from these new, soaring schemes. As with any innovation, there are lessons to be gained, many of them specifically pertinent to the high-rise space. Key issues that come into play where prefab scales the heights include construction methods, wind loads, logistics and fire safety. There is also a compelling view that decisions to ‘go prefab’ should be made at the beginning of the design process to achieve the best outcome.

Phil Gardiner, Managing Director of engineering firm Irwinconsult offers an exemplar of one high-rise project where an off-site methodology supplied not only efficiencies and solutions but a steep learning curve.

At the time of its completion last year, the Soho Tower in Darwin achieved status as the world’s tallest volumetric modular pre-fab building. Totalling 29 levels, the tower was designed to incorporate a basement and eight floors built with conventional reinforced concrete, followed by 21 levels of volumetric modular apartments, 100 per cent manufactured in China.

Initially designed with a conventional construction methodology in mind, the choice to go modular was driven by a skilled labour shortage in Darwin that had caused labour costs to spike. Another driver was the foundation condition of the site, primarily underlain by soft rock, meaning the allowable peak bearing pressure on the site was 500 KPa. “This was a challenge for such a tall building that would typically require a full raft across and beyond the tower footprint, making the lighter construction methodologies of a modular build an advantage. Meanwhile, the severe cyclonic conditions in Darwin resulted in high wind loads, negating the use of self-braced modules. Instead a traditional core with an outrigger wall was considered the best structural solution.”

“Unlike many modular systems, a concrete floor was used with concrete columns poured on-site into formworks inside the modules,” says Gardiner. “Lateral stability was achieved through the central core using a modular precast concrete system. As the contracts of sale were in place for the apartments the developer opted to keep the concrete floors.”

Initially steel framed solutions had been mooted, however these were replaced for a variety of reasons (from the location of plumbing risers which would have necessitated penetrating multiple steel joists to connect plumbing elements, to the risk of the local tropical climate creating condensation on the steelwork between each module) and concrete was determined as the best material. “The concrete floor was designed as a slab with perimeter beams and cross beams located to intersect with the perimeter columns. Each slab contained a number of elements, including cast in steel fitments for the attachment of wall framing and mullions for glazing.”

While challenging, changing methodology from conventional to offsite also furnished opportunities, says Gardiner. “The real game changer was the fact that we didn’t need to rely on relatively small steel columns with fire rated cladding. The solution we arrived at of concrete columns and floors meant that essentially we could have gone as high as any other conventional build.”

Wood & Grieve Engineers now has considerable form in the pre-fab space, having worked on a variety of projects including, Tribe Hotel, The Schaller Studio and La Trobe Tower in Melbourne, a 44 level residential tower by developers Longriver Investments with design by architects Rothelowman.

Considered a landmark in the high-rise prefab space, the recently topped out La Trobe Tower development was initially conceived as a conventional build and transferred to a modular prefab solution due to the time, access and disruption constraints of its Melbourne CBD location.

It was ultimately delivered around 30 per cent faster than comparable projects, using Hickory Group’s innovative construction methodology and elements that included integrated structural prefabrication, a proprietary façade system and bathroom pods. John Lucchetti, Hydraulic & Fire Protection Section Manager at Wood & Grieve Engineers, cites the “key drivers” in pre-fab, which include the necessity to design up front and conceive each module as extensively as permissible prior to construction.

“This is necessitated by the repetition of each module as part of the building’s structure and also by the fact that, unlike a conventional build, these modules are being manufactured elsewhere at a factory.” “Another key factor in my experience is that you’ve got to have a very fine tuned understanding of how ‘complexing’ works; in other words, how each module interfaces and connects with other modules and with the building as a whole, which is different for every building.”

Pre-fab construction also requires a high level of clarity with contractors in terms of scope delineation. “You have to be very clear about which elements are going to be assembled on site and which are going to be essentially manufactured in a factory and how those elements slot together.”

This requires a radical re-think of the sequencing of the building and how and in what order the elements are conceived and installed. It’s perhaps no surprise that traditional working methods often need to be re-thought or overhauled, as Lucchetti, who is currently contributing to a group working on a new modular construction code of practice, confirms.

“Much of the traditional building code doesn’t cover many of the practices and approaches required by modular construction. Just as one example, you need to spend significant design hours working out the manufacture, transportation and logistics and lifting of modules.“

Lucchetti says he’s personally inspired by the pre-fab space. “My journey has spanned five or six years. I used to be in manufacturing, so a lot of the processes and systems involved make sense to me. It’s great to be able to apply lean manufacturing principles to building engineering, minimising waste and maximising efficiencies. We’re getting more and more enquiries about pre-fab or modular solutions from our clients.”

He adds that BIM software has proven a boon in modular construction. “BIM is great because of the fine grained level of precision it offers in terms of coordinating all the elements accurately. It allows you to convey a very clear picture to modular constructors of what’s required. The next evolution will be to use BIM at the manufacturing stage to create the key elements of the modules themselves. It’s already being used in some settings to set up dimensions and projections for jig-tools for example. I see an exciting future where BIM can be used for parametric modelling. So for example when you’re designing a module and something has to be altered dimensionally, BIM can be used to re-calibrate all the relevant dimensions across all modules.”

Given the recent success of the La Trobe Tower, Hickory Group is arguably leading innovation in the pre-fab high rise market with its solution, Hickory Building Systems (HBS). “Most of the prefab systems on the market are still geared towards housing our low-rise developments,” says Michael Argyrou, Hickory

Group Managing Director. “As high-rise builders in our conventional business, it made sense to bring our prefab capability in line with the rest of our business offering, so we began developing technology that would allow us to apply the same principles and benefits to larger, inner-city builds.”

“Hickory Building Systems’ key point of difference is that it’s not a one-size-fits all approach. We use interchangeable componentry that’s best for the project. That might involve bathroom pods, prefixed facades, precast slabs and structural steel frames, depending on the site and the construction approach.”

Another advantage of HBS is that it allows a more collaborative approach with architects and consultants in the planning stages, he says. “We can very quickly produce BIM models that show how the building will be broken up for manufacture, which helps resolve design issues, maps structure and consolidates spatials in order to achieve workable shop drawings and a bill of materials for manufacture.”

“We have also developed parametric, ‘smart’ BIM models that can be used by architects to map an entire building structure and facade for prefabrication using the Hickory Building System.”

Wind-loads and structural engineering considerations were a key focus in the development of the system and Hickory has an in-house structural engineering expert that works on all HBS projects.

Hickory Group’s innovative construction methodology was key to the La Trobe Tower in Melbourne.

Soho Apartments – the project set new boundaries for Irwinconsult (Image credit: Urban Safari).

The University of Tasmania (UTAS) has also utilised Interpod bathrooms.

“We find the real benefit to developers is the time saving; we can complete a high-rise project 30 – 50% faster, this could mean a 12 months faster ROI. As the quality is increased we also find there are fewer defect-rectification costs post completion.”
Michael Argyrou, Hickory Group

Argyrou also notes that other large builders are using Hickory Group’s Sync modular bathrooms, to gain quality and time efficiencies on the fit out cycle.

“There is definitely opportunity to look at what other elements of the build can be taken off-site to streamline the build process. An example of that is our Sync bathroom business developing separate laundry pods, which we’ll be providing alongside bathrooms for a large-scale project in NSW.”

While an abiding perception remains that prefab is cheaper, Argyrou says this isn’t always the case. “[It] may be true with some low-spec modular systems, but these are often are quite limited in application. As our system is high-spec and high quality we find the cost to be comparable with conventional construction.”

“We find the real benefit to developers is the time saving; we can complete a high-rise project 30 – 50% faster, this could mean a 12 months faster ROI. As the quality is increased we also find there are fewer defect-rectification costs post completion.”

With the world’s cities continuing to grow and spiking land prices driving demand, in terms of offsite constructed high rises, Argyrou indicates the sky’s the limit.

“Our systems have no theoretical height limitations. We’ve just erected Australia’s tallest prefab building – a 44-storey tower, and are now working on another 60 level project in Melbourne. In fact building with this type of system is more beneficial in projects over 30 levels, so you can get the economies of scale in manufacturing. “

HIGH RISE POD MARKET RIPE FOR GROWTH

High-rise builds are characterised by heavy and repetitious demand for certain room functions, such as bathrooms; service-heavy rooms traditionally requiring the input of numerous trades and therefore triggering unforeseen cost and schedule distortions.

Innovative companies are working to remove such ‘headaches’ by supplying fully fitted rooms or ‘pods’ for easy inclusion into pre-fab builds. One such company is NSW based Interpod Offsite.

Interpod Marketing & Communications Manager Eliza Hutchison says one industry sector that has embraced the benefits of prefab in the high rise market is student accommodation, fuelled by the growth of what is now one of Australia’s largest economic sectors – education services

“The growing number of students seeking homes in inner city locations means that the delivery of quality student accommodation facilities in a timely manner is paramount to educators,” she says. “In fact, Interpod has now delivered over 5000 bathroom pods in the student accommodation sector alone, with another 5000 plus in the pipeline.”

Interpod has worked with the University of Melbourne in housing 648 students in a soon to be completed Leicester Street development in partnership with Campus Living Villages and Watpac. Another student accommodation project in Brisbane will see 785 dwellings built across two 15 and 17 storey towers, with Interpod to provide an end-to-end bathroom solution.

Beyond the education sphere, she confirms the need for speed and quality in the services industry has seen Tune Hotels and Arrow International enlisted Interpod to provide nearly 300 bathrooms over eight floors in a tight timeframe.

“Bathrooms account for a significant amount of defects on large projects and yet only account for a very small part of the total budget. The bathroom is one of the smallest rooms in the entire dwelling, and yet it is also one of the most laboriously intensive to build, requiring input from nearly every building trade, moving in and out of a single room. Often over three months will be allocated to bathroom construction on a project schedule. By contrast, Interpod begins manufacturing bathrooms months in advance, or parallel to the construction schedule. This allows for their delivery and installation to coincide with the project schedule.”

The result is a high degree of project certainty for architects, developers and builders, she says. “When you consolidate the entire bathroom build to single supplier, you are left with a single cost, a single supplier and a single, defect-free guarantee for the bathrooms in your project.” ■