“CLT with TLC”

– Extracts from a Sydney Morning Herald article first published 31 March 2025, written by Julie Power

Luigi Rosselli’s new homes often feature rammed earth: a sustainable material affordable only for those with the time to build them, deep pockets to cover the costs, or both.

Now the Sydney architect is experimenting with another highly sustainable material on a row of four terraces in Bondi Junction with walls that go up “like a Lego kit”.

Designed as a low-cost version of a terrace, the homes use prefabricated cross-laminated timber (CLT) made from layers of wood stuck together to shrink construction time from “one-and-a-half years [conventional build] to just six months.”

For Rosselli, the build-to-rent project called “CLT with TLC” is a carefully documented experiment to see what can be done with speed and economy to mitigate the housing crisis, increase density and reduce carbon associated with building projects. (He added that the homes would also provide him with retirement income – the project, which provides much needed stable rental accommodation, was conceived and entirely funded by Rosselli himself).

The [2025] federal budget included $54 million to accelerate uptake of modern construction methods that are faster and more efficient housing solutions which reduce carbon.

When Rosselli posted a time-lapse video on Instagram showing the 80-metre square terraces going up on the site of a single-storey home, more than 900 people responded. “Wonderful to see an architect who is usually associated with the highest end of bespoke residential architecture tackling a project like this,” one commenter said.

Using CLT allowed a plan to be rapidly duplicated, Rosselli said, making it ideal for rapid construction of low-to-medium-density housing.

The engineered wood was more expensive than traditional studwork, but it was faster and saved money elsewhere in the build.

“The building industry is slow, and it’s getting slower,” he said. “I’ve worked for 40 years in Australia, we used to build a house in nine-twelve months maximum. Then it was one year and a half. Now it’s two years.” This wasn’t the fault of workers, Rosselli said, but increasingly complex regulations, qualification requirements and management of risk and liabilities that often required one trade to finish before another could start.

Responding to comments on Instagram, Rosselli said “the big difference in time and accuracy. [It is] six months for the whole project including some traditional trades [such] as tilers and windows. This is more than 50-70 per cent of a standard building site duration. Therefore, substantial reduction of overheads [such] as foreman, insurance, scaffolding and other expensive overheads. Precision is also helping on ordering every out of site item in advance without risk [of] not fitting.”

It was the practice’s first time using CLT “And I must say, it won’t be the last. It’s a really wonderful material. It’s so precise the way they manufacture cross-laminated timber panels.” His practice was tracking costs and the project’s impact on the environment. The manufacturer, XLAM, estimates that the use of 173 cubic metres of CLT, made from pine grown in Australian plantations, would store 80.63 tonnes of CO2-eq (carbon) – the same environmental impact as taking sixty cars of the roads for a year.

Architect and sustainability expert Caroline Pidcock said it was “absolutely critical” that designers such as Rosselli led the way with beautiful and sustainable builds. “There is real responsibility because architects look up to them, the press does, and clients do too.”

Rosselli has spent his career trying to educate his clients, many at the upper end of wealth in Australia, on the benefits of using recycled materials.

“The impact that I can have with them is sometimes 10 or 12 times that of a small project,” he said.

“If a can convince a millionaire, a billionaire, to reuse an existing building… it has greater impact. We’ve been quite missionary in trying to convince clients to use rammed earth, which has a very low CO2 component.”

Monash University professor of practice Karl-Heinz Weiss introduced CLT to the UK market in early 2000 and has been involved in more than 150 projects.  Weiss said unlike concrete, which produces carbon, CLT is made from timber that stores carbon, and was the only sustainable and renewable building material that can be used as scale.  The longest panels were about 3.3 metres by 16 metres. “That gives you speed of assembly because you are not having a lot of little pieces” he said.

Australia had two factories producing CLT, and others manufacturing glue-laminated beams and components.

Weiss said CLT was typically most suitable for projects from four storeys upwards. Larger projects using CLT, such as the 180-metre Atlassian headquarters, needed concrete and steel for stability.

Sustainability Stats

Based on the use of 173 cubic metres of CLT, the project stores approximately 80.63 metric tonnes of CO2 that would otherwise be in the atmosphere.

Based on the growth rate of Australian plantations alone, it would take just 29 minutes to regrow the 173 cubic metre volume of CLT timber used in the project, providing a carbon reduction equivalent to taking 60 cars per year off the road.

Efficient floor plans result in just 2m² of circulation space per property.

Bricks recycled from the demolition of the house that previously occupied the site were used to construct the brise soleil screens to the front façade of the terraces, and for exterior paving.

The roofs are tiled with terracotta tiles, whose manufacturing process is lower in emissions than that of metal roofing.

Hot water is provided via heat pump hot water units, which are [up to] seven times more efficient than standard electric hot water units.

Four 3000 litre water retention tanks provide water recycling.

The earth wool insulation installed is made from 80% recycled materials.

The lime render finishes have a lower carbon footprint than standard paint or stain finishes.

Carpets are of natural wool, with an underlay made entirely from recycled materials.

Two sickly trees were removed to make way for the development, and replaced by five native Eumundi quandong trees, that will attract both nectar-feeding and seed-eating birds.

One glaring omission from this list of sustainable features is solar panels.  This was not an intentional decision made by Luigi Rosselli Architects, rather it was a condition of consent imposed by Council in their approval of the development application that the panels proposed were removed!  They were asked to reconsider this condition but, bafflingly, they refused!