Within days, owners and residents of Sydney’s Mascot Towers are expected to learn what went so wrong with the heavy mass concrete building which was evacuated almost four years ago and now faces demolition.
The 10-storey building at 1-5 Bourke Street, built at a cost of $42.5 million, is 12 years old with 131 units across two towers in a complex which includes ground-floor shops and restaurants.
The Owners Corporation Network has been told it will cost $38 million to fix the building, which would blow out to $64 million including interest over the course of a 15-year loan. But this won’t happen.
Mascot Towers Evacuation: Uncovering the Cause of Structural Failures
In June 2019, residents and tenants were evicted after cracks were discovered in the basement and carpark area. The problem was spotted during construction work nearby.
A building engineer who carried out an inspection of the cracks “raised concerns over the safety for residents in the building” and the building manager decided to evacuate.
In a notice from the apartment block’s strata on June 13, 2029, residents were told about the installation of temporary building props in the carpark.
“This is in response to an ongoing and persistent cracking and structural deformation observed within the primary support structure and the facade masonry,” the notice read.
Experienced structural engineers contacted by Wood Central understand the failures at Mascot Towers were discovered after excavation started on a next-door building along with a combination of ground water factors.
“We must realise that such mass concrete structures are three times heavier than a mass timber equivalent,” a Sydney engineer said.
“That’s a hell of a difference when designing foundations,” he said.
“So, it’s a no-brainer that timber greatly reduces the risk of a foundation failure; it’s much lighter than concrete.”
Mass Timber vs. Concrete: Comparing Foundation Risks and Weights
That said, however, mass timber producers must keep on top of potential water ingress problems. The reality is that sprinklers can and do fail as was the case at a condemned multi-level LVL building in London.
Also, mass timber’s fire resistance attributes should continue to be monitored regularly.
Timber Span Recommendations: Addressing Long-Term Creep Issues
Meantime, it is understood that Arup, the world’s largest promoter of mass timber design, is considering recommending smaller timber spans while Australian manufacturers press on with larger spans meeting the preference of modern timber design.
Timber spans at the Lend Lease Barangaroo project in Sydney were 6 m. Arup now is pushing for 4.8 m spans in mass timber construction.
Some industry observers say this might be linked to future thinking on “long-term creep issues” and Arup wants to get ahead of this. On occasion, long length beams, at times, can give the appearance of sagging.
Reducing Carbon Emissions: Early-Stage Design Decisions for Buildings
Meanwhile, the impact of multi-storey building design and construction considerations on embodied carbon emissions, cost and operational energy have been revealed for the first time by researchers at the Universities of Cambridge and Bath in England.
Published March 23, 2023, using a computer model, they estimate that up to six gigatonnes of carbon could be saved by 2050 if new multi-storey buildings follow certain recommendations during the design process.
All these recommendations, which could also save between 28 and 44% of annual heating and cooling costs, use technology that is currently available.
Construction and operation of buildings account for more than one-third of global emissions and energy use. While buildings are a large part of the current problem, they are also a significant lever for change, say the university researchers who explored the decisions architects, engineers and urban planners must negotiate.
For their study, the researchers looked at shape, size, layout, structural system, windows, insulation, ventilation, and use parameters for both residential and office buildings across different climates.
The researchers built a model that allowed them to estimate, for the first time, the relative importance of these early-stage design decisions in a whole building context.
The study found that increasing building compactness, using timber or steel instead of concrete frames, smaller windows with the optimal glazing for a given climate, and using mechanical ventilation with heat recovery, are the best way to decrease embodied emissions and operational energy.
The most significant effects on construction costs meanwhile were the choice of frame material and whether to install mechanical ventilation.
For both residential and office buildings, the choice of structural frame type has a large effect on both embodied carbon – the amount of carbon emitted by the construction of a building – and cost.
The researchers found that lower-cost frame types tend to be more carbon intensive and vice versa, pointing to a significant trade-off. In comparison, the lowest carbon solutions are cross-laminated timber floor slabs with laminated beams or steel frames.
Also, as the number of storeys increases, so do embodied carbon values.
The choice of cladding is also a significant factor.
Lead author Dr Hannes Gauch, research associate in embodied energy and emissions in construction at the department of engineering, University of Cambridge, said: “It was surprising to us that insulation thickness and thermal mass, which are usually given a lot of consideration by building designers and researchers, are minor factors in determining the efficiency of a building.
“Choosing lightweight cladding over brick, for example, has a much more significant impact,” he said.
“Our findings show that to design low-carbon buildings we need to focus on efficient shapes (boxy) and structural frames (shorter spans, more timber), limit window sizes, and employ ventilation with heat recovery.”
