Sustainable Builders Yak

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What happens when you put hemp into a structural brick?
Will Stewart, director and co-owner of Natural Brick, joins us to unpack how his team is rethinking one of the most familiar building products around, from what goes into the mix to how it performs once it hits the wall.
Natural Brick’s current brick uses hemp grown in NSW, making up around 45–50% of the mix by volume. Rather than being kiln-fired, the bricks are naturally cured using solar heat over an eight-week process. The result is a load-bearing single-skin brick that has achieved an unconfined compressive strength of more than 11 MPa, with recent testing closer to 15 MPa, and an impressive 180/180/180 fire resistance result.
Will gets into the practical details builders and architects actually want to know: how the brick handles moisture, salt attack and weathering, why it needs to be laid dry, what the long curing time means for project planning, and where the current carbon assessments fall short.
We also get into the more experimental side of Natural Brick, from algae-based bricks and bricks made from construction waste to furniture made from recycled stone and even a bone terrazzo table.
And then there’s the custom work. Natural Brick has developed an in-house mould-making process that can bring a custom curved brick mould down from a typical five-figure setup to around $1,200, while allowing moulds to be reused across projects.
It’s a conversation about what happens when you take a conventional building product, question how it’s made, and start looking at waste, materials, manufacturing and performance differently.
EPISODE HIGHLIGHTS
How Natural Brick makes a structural brick using around 45–50% hemp by volume
Why Natural Brick uses solar curing instead of kiln firing or mechanical curing
The testing behind the product, including 11+ MPa compressive strength and a 180/180/180 fire resistance result
What builders need to know about moisture, durability, weathering and laying the bricks
How custom curved brick moulds can be made for around $1,200 rather than a typical five-figure setup
The reality of measuring embodied carbon, including the limitations of current assessment processes
What Natural Brick is experimenting with next, including algae and construction-waste bricks
Inside the furniture studio, where recycled stone, industrial by-products and even animal bone become new materials
CHAPTERS
0:00 - Meet Will Stewart and how Natural Brick began
1:58 - Building schools in Kenya, and what it taught him
6:10 - Back to bricks: why mud bricks didn't work
7:36 - The Lutyens brick and its long format
9:50 - How the brick is actually made
12:14 - Switching to hemp, and why it works better
13:49 - Solar curing instead of a kiln
14:29 - Inside the mix: hemp, sand, cement, fly ash, pigment
17:27 - The carbon numbers and the Think Brick study
20:10 - Where carbon assessment falls short
21:32 - Compressive strength and the 180/180/180 fire result
23:01 - Vapour permeability, moisture and laying dry
24:54 - Thermal performance and R-value
27:06 - R&D: the algae brick and construction-waste bricks
36:59 - A curved apartment project, and reusing moulds
42:19 - Weathering, sealing and cleaning without acid
46:38 - What's next, and the furniture side
54:39 - The biggest constraint, and getting to low carbon
56:05 - Quickfire
ABOUT THE GUEST
Will Stewart is director and co-owner of Natural Brick, a New South Wales maker of handmade, hemp-based masonry. He came to bricks after around six years building schools in Kenya and Uganda, then a stint in beverage sales, and now runs the business with two co-owners out of a solar-powered factory in Warragamba, at the foot of the Blue Mountains.
LEARN MORE
Natural Brick: https://naturalbrick.com.au
Sustainable Builders Alliance (SBA): https://www.thesba.com.au
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Most climate conversations in sport start with the elite game. Tom Campbell starts with the clubrooms: a grassroots footy club whose power bill dropped from $9,000 a year to $900, with the $8,000 difference going straight back into the club.
Brian and Simon are joined by Tom Campbell, co-founder of Footy for Climate, which he started while playing at North Melbourne, in the season the Black Summer bushfires filled the training track with smoke. Its Power Forward program puts solar and battery systems onto community footy clubs so the savings stay in the community game.
Most of the hour lands on the part builders will recognise: the clubrooms are owned by councils, the tenants pay the bills, and almost nobody is funded to fix them. Campbell is blunt that climate action has to save money before a club or council will touch it, which is the same case builders make for efficiency, insulation and retrofit every day. The conversation also gets into what the savings unlock, from concussion screening at community level to why a changing climate is already moving the fixture.
EPISODE HIGHLIGHTS
Power Forward, and what solar plus battery does to a community club's power bill
Why councils own the clubrooms, and why that is the hardest part to solve
Why solar on its own no longer stacks up, and what winter footy does to the numbers
What the savings unlock, including concussion screening at community level
The $20 million that would retrofit 220 Victorian clubs and save $3.5 million a year
CHAPTERS
0:00 - Meet Tom Campbell, and why Black Summer started Footy for Climate
4:07 - Offsetting player flights, and why that model stopped
7:10 - Power Forward, and a club power bill from $9,000 to $900
11:24 - The council owns the clubrooms, so how does a club get solar?
15:16 - Why solar alone no longer stacks up without a battery
18:48 - What the savings unlock, beyond the carbon
24:34 - Is the AFL on board, and does it fund the work?
26:49 - Mandatory reporting, and the clubs already moving
31:16 - Having a climate conversation inside a footy club
35:32 - An open chequebook, and the $20 million Victoria needs
39:17 - Concussion, and neuropsych screening at community level
41:22 - Five years out, and 500 clubs by 2030
43:25 - What players know, and the media training behind it
47:42 - Climate is already moving the fixture
50:15 - What keeps you going when progress is slow
53:05 - Quickfire
ABOUT TOM CAMPBELL
Tom Campbell is co-founder of Footy for Climate, which he started over five years ago while playing at the North Melbourne Football Club. He played 14 years of AFL across Melbourne, St Kilda, North Melbourne and the Western Bulldogs before retiring in 2026. Footy for Climate began by offsetting player flights and now runs Power Forward, a program putting solar and battery systems onto grassroots footy clubs so the savings can go back into the community game.
LEARN MORE
Footy for Climate: https://footyforclimate.org.au
Sustainable Builders Alliance (SBA): https://www.thesba.com.au
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Australia is the seventh most forested country on earth, yet it imports around $5 billion more timber than it sells, and the gap grows every year. Matt de Jongh, a forester of about 25 years and now with Responsible Wood, the body behind timber certification in Australia and New Zealand, explains how that happened. His blunt version: at home, we have run out of wood.
Most of the conversation digs into what "sustainably managed" actually means on the ground. Matt breaks down the difference between certified and uncertified timber, how the "no deforestation" rule works when trees are still being cut, and why independent third-party auditing, not a landholder's word, is what sits behind a Responsible Wood or PEFC label.
From there it turns political. Matt argues that ending native forest logging in Victoria and WA has pushed demand onto Tasmania and onto imports from countries with weaker rules, and he uses the Pilliga koala population as his example of what happens after active management stops. The episode also covers mass timber, the carbon locked inside a timber product, and why architects keep coming back to wood.
EPISODE HIGHLIGHTS
Why the seventh most forested country still imports about $5 billion more timber than it exports
What "no deforestation" actually means: permanent land-use change, not selective harvest and regrowth
Certified vs uncertified timber, and how independent auditing backs a Responsible Wood or PEFC label
The Pilliga koala argument, and what Matt says happened after a managed forest became a national park
Mass timber, stored carbon and the case for building in wood
CHAPTERS
0:00 - Meet Matt de Jongh, and the science of forestry
4:33 - What "sustainably managed" actually means
5:17 - Plantations, native forests and how thinning works
7:33 - "No deforestation" defined, and who checks it
13:22 - Forest certification, PEFC and Responsible Wood
18:25 - Certified vs uncertified timber, and the illegal logging laws
24:08 - Why timber is the ultimate renewable, and biogenic carbon
26:55 - The forests that aren't certified, and small landholders
30:25 - WA's gum plantations and the scheme that planted in the wrong place
35:05 - The $5 billion question: a forested country that still imports timber
39:12 - A shrinking forest estate and the housing crisis
43:24 - Engineered timber, mass timber and traceability
46:17 - Is there a fix, and why it is political
49:09 - Victoria, Tasmania and the media story
51:19 - The Pilliga, koalas and what happens when management stops
1:05:47 - The silver bullet: procurement and wood encouragement policies
1:11:15 - Quickfire
ABOUT THE GUEST
Matt de Jongh is a forester with around 25 years in the industry, from operational forestry across New South Wales to policy roles with the Australian government, and he is a director of Forestry Australia. He now works with Responsible Wood, the standards body that runs forest and chain-of-custody certification in Australia and New Zealand and represents PEFC locally.
LEARN MORE
Responsible Wood: https://www.responsiblewood.org.au
Sustainable Builders Alliance (SBA): https://www.thesba.com.au
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Australia's National Construction Code climate zones and NatHERS and PHPP models built on them, are calculated from climate averages that are no longer holding. When Brian raises this, Monash University climate scientist Ailie Gallant stops and admits it's a gap: she hadn't considered the building code angle, and says she'll take it back to her team to look into.

The bulk of the episode is a plain-language climate science primer, delivered without jargon by someone who does this for a living. Ailie explains the greenhouse effect as a window that different gases open and close, walks through carbon dioxide moving from 280 to 432 parts per million, and puts that in context: roughly a 55% increase in eighty to a hundred years, where comparable past shifts took millions. She also explains why the scientific consensus holds despite researchers actively trying to discredit each other's work.

For builders and designers, the practical content is in what comes next. Ailie sets out the regional picture: drier winters and more time in drought across southern Australia, hotter and more humid up north, fewer cyclones but more intense ones, and rainfall arriving in short violent bursts rather than steadily, which is a drainage problem before it's anything else. She's also cautiously optimistic: the worst emissions scenarios modelled a decade ago now look unrealistic, and the conversation lands on two to three degrees rather than five or six.

EPISODE HIGHLIGHTS
Whether NCC climate zones will shift and why a 100 year house in Melbourne might need to be built for central New South Wales
"This is not our new normal, this is our changing normal" why updating the code once won't be enough
Carbon dioxide from 280 to 432 parts per million: a 55% jump in a century, where past shifts took millions of years
Hotter and drier down south, hotter and more humid up north, and cyclones that come less often but hit harder
Rain arriving in short violent bursts instead of steadily: a drainage problem waiting to happen
LEARN MORE
Monash University: Ailie Gallant: https://www.linkedin.com/in/ailie-gallant-b36839a9/
ARC Centre of Excellence for Weather of the 21st Century: https://www.21centuryweather.org.au/
Sustainable Builders Alliance (SBA): https://www.thesba.com.au

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Andy Marlow's definition of efficiency in passive house and airtightness will annoy some people: it's doing the bare minimum required to clear the hurdle, which he says is much the same as being really bloody lazy. Andy is a director at Envirotecture, a long-time passive house advocate and former Australian Passive House Association board member — and he thinks the industry's obsession with beating its own numbers is costing builders money for no measurable gain.
The core of the conversation is where the point of diminishing returns actually sits for high performance. Once a building is genuinely airtight, the model becomes predictable (you can't model a sieve) and that predictability is what lets you cut back everything else. Andy walks through the UK apartment work presented at the Passive House Conference where parts of the building are deliberately built worse than code because the form factor absorbs it, the concrete footings nobody needs to perfect, and the one thing you can never compromise on: condensation risk.
Brian makes the same case from the other direction — that a decade of chasing certified air-tightness is what teaches you how much performance you can buy for far less. They get into the airtightness arms race between builders, the bloke who hit 0.06 and probably wasted his weekends doing it, achieving 2 ACH cheaply through the plasterboard line, and whether a tiered certification pathway would drag the volume market across the line. Andy also explains the relaunch of Passive House Design & Construct as pre-designed-only homes — the same logic applied to design fees.
EPISODE HIGHLIGHTS
An educated way to cut corners.
The airtightness arms race — 0.6 versus 0.5 versus the 0.06 warehouse, and where the ego takes over from the engineering
Condensation risk as the one thing you don't get to compromise, and Andy's caution on loosening airtightness
Low Energy Building as the sensible tier down, and why a 300mm-plus wall isn't always financially sane
Health, comfort and longevity as the real product — "no one cares about energy efficiency"
Applying the same logic to design: the relaunch of Passive House Design & Construct as pre-designed homes you can't modify
LEARN MORE
Envirotecture: https://www.envirotecture.com.au/
Passive House Design & Construct: https://passivhausdc.com.au/
Sustainable Builders Alliance (SBA): https://www.thesba.com.au
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Sustainable Builders Alliance (SBA): https://www.thesba.com.au