Bega hempcrete block house

Supplied by: Respirabuilt
Builder: Owner-builder

Chris Hopkins is an owner-builder in the Bega Valley, and like many people drawn to hempcrete, his interest was anything but casual. He had been thinking about building with hempcrete for a long time, reading, researching, and gradually working out how he wanted his house to come together.

The original plan was ambitious but clear. A full cast-in-situ hempcrete build, done by Chris himself. No shortcuts, no compromises, just a commitment to doing the job properly. 

The Challenge

On the northern side of the house, wall heights reached around four metres. The house also required 33 tonnes of hempcrete, a substantial load to wet-mix on-site for cast-in-place hempcrete.

At that scale, casting hempcrete becomes a very different exercise. 

• Formwork needs to run the full height on both sides of the wall

• External formwork is harder to set externally on bare earth on scaffolding, particularly in the heat.

The Approach

Having this in mind, we presented the Cast & Block method, which ultimately changed the direction of the build. 

Cast & Block is a hybrid hempcrete system that combines pre-formed hempcrete blocks with targeted in-situ casting, requiring only formwork on the internal side of the hempcrete wall

The strategy shifted to a hybrid approach. 

• Hempcrete blocks were introduced on the external face

• Casting was limited to the internal side. This made it possible to run up the external wall cleanly past the rafters and meet the ceiling wrap without the need for complex formwork between each rafter bay at height.

What would have been a complex, labour-heavy process became far more manageable, without compromising the continuity or integrity of the thermal envelope. This wasn’t a step back from performance. It was a refinement of the strategy, shaped by the realities of the site, the scale of the walls, and the fact that this was an owner-builder project aiming for a very high standard.

Work at Scale

With the build involving around 328 square metres or 33 tonnes of hempcrete, efficiencies add up quickly.

Using blocks on the external face significantly reduced the amount of formwork required. Internally, casting could be carried out with a tighter crew and a more predictable rhythm. 

Full Cast in situ requires a team of

• One mixer person

• Three people are placing hemp

• Two skilled Carpenters / formworkers

Cast & Block requires a team of

• One mixer person

• Three people are placing hemp

• One person managing formwork.

Fewer moving parts, fewer people working at height, and fewer moments where things could drift off course.

There was also a material benefit. A conventional full cast hempcrete wall sits at around 300 millimetres thick. By combining external blocks with internal casting, the total volume of hemp mixed on site dropped to roughly two-thirds of what a full cast system would have required. That reduction allowed more time and attention to be directed toward the internal feature walls, where finish quality and consistency were always going to be visible.

The blockwork also helped the project reach lock-up sooner, allowing external rendering to follow without long delays. It kept momentum on site without rushing decisions.

Cost and Efficiency 

From a cost and efficiency perspective, the Cast & Block approach delivered clear advantages without pushing the project into specialist territory. Labour demands were kept under control despite the scale of the walls. Work progressed in a steady, predictable sequence rather than in physically demanding peaks. Casting is also simply more physically demanding, so keeping that process to a shorter timeframe avoids exhaustion from marathon-length jobs

Project Snapshot

• Total hempcrete area: ~328m²

• Wall height (north elevation): ~4 metres

• Construction method: Cast & Block (external blocks, internal casting)

• Crew setup: 1 mixer, 3 placing hemp, 1 managing formwork

• Outcome: Earlier lock-up and smoother transition to external rendering

Importantly, these efficiencies were achieved without compromising performance. By using blocks on the external layer, the wall delivered around a 40% improvement in thermal performance compared to cast hemp at the same thickness, while remaining continuous, robust, well resolved, and achievable within a high-quality owner-builder budget.

The Result

The finished house reflects the level of attention Chris brought to the build from the beginning. As an owner-builder, he approached the project with patience and intent, and the result shows it. The work is precise, well resolved, and sits comfortably alongside projects delivered by experienced professional builders.

More importantly, the house performs as it should. The thermal envelope is continuous, and key junctions are resolved cleanly.

Rather than simplifying the project's ambition, the Cast & Block approach made it achievable. It allowed the build to respond to its constraints while maintaining a clear focus on quality, performance, and finish.

Trusted by Clients

This project shows how method selection matters when working at scale. In this case, a deliberately selected hybrid system kept the build under control while delivering the required performance.

For owner-builders, it demonstrates that complex projects don’t require an all-or-nothing approach. For builders and designers, it shows how hempcrete blocks can be applied selectively to suit site conditions, wall heights, and sequencing, rather than forcing a single method across the entire build.

Respirabuilt supported the project by guiding technical decisions, advising on sequencing and interfaces, and ensuring the system was used where it made the most sense. We supplied the mixer, hemp, and lime binder for the cast component, and provided on-site support during installation. Respirabuilt also provided a solid bank of knowledge and expertise for all of the pre-construction phase, up until completion.

We also had an in-depth interview with the owner builder to discuss his experience of working with you Cast&Block system which you can check out HERE

If you’re working through a build with challenging wall heights or complex conditions, we’re always happy to talk it through. Get in touch to discuss how Cast & Block might support your project.