Rammed earth walls bring high thermal mass, fire resistance and raw beauty – but the cement that stabilises them carries a carbon cost. A complete guide to building with earth.
Rammed earth is one of the oldest walling techniques still in use, and one of the few that arrives on site as little more than graded dirt. Damp subsoil – a blend of gravel, sand, silt and clay – is compacted in layers inside temporary formwork until it sets into a solid, load-bearing wall. The clay binds the coarser particles; the compaction does the rest. The result is a monolithic wall with the banded, sedimentary look that gives the material its appeal, and a set of properties that are frequently misread.
The technique is ancient and widely distributed, from sections of the Great Wall of China to the tapial walls of the Alhambra and the pisé farmhouses of the Rhône valley. In contemporary Australian practice it has a particular stronghold, with builders working in the technique across Western Australia, Victoria, Queensland and beyond. Most of that contemporary work is stabilised – a small amount of cement added to the mix – and that single decision, more than any other, determines what the wall costs the climate.
Hero image:
Earth Ship by Luigi Rosselli
and Alwill Interiors,
photo by Prue Ruscoe.
What is rammed earth made of, and how is it built?
A rammed earth wall is built in place. Formwork is erected along a concrete footing or slab, and a damp mix of earth and water – usually with a stabiliser and sometimes a waterproofing admixture – is shovelled in and compacted in increments of roughly 150 millimetres using pneumatic tampers. Each layer is rammed before the next is added, which is what produces the horizontal striations across a finished wall. The formwork is typically stripped the following day to reveal an off-form face that needs no lining or plaster, only sealing.
The ideal mix is well graded, with enough clay to bind and not so much that the wall shrinks and cracks as it dries. Colour comes from the earth itself, or from oxide pigments and material drawn from different quarries, which is why rammed earth reads as belonging to its region even when the mix is engineered. Services – electrical conduit, plumbing – are set into the formwork and rammed in as the wall goes up, which means the trades have to be coordinated well before the wall exists. It’s an unforgiving sequence: rammed earth is difficult to modify after the fact, and a mistake set into a wall can be expensive to correct.
Walls are commonly built at 300 millimetres thick for a solid internal wall, and around 450 millimetres where an insulating core is introduced. External walls on exposed or rural sites are often thicker again – 400 to 600 millimetres is not unusual.
Stabilised or unstabilised: the cement question
This is the distinction that matters most, and the one most often skipped.
Unstabilised rammed earth is earth and water alone, compacted and left to cure. It’s about as low in embodied carbon – the emissions locked into a material before a building is even occupied – as a wall can be, and at the end of its life it can return to the ground. Its weakness is water: an unstabilised wall needs what earth builders call a good hat and good boots, a generous roof overhang and a damp-proof base, to keep driving rain and rising damp off the earth.
Stabilised rammed earth adds a binder, usually 5 to 10 per cent Portland cement by weight, sometimes lime. The cement improves compressive strength, weather resistance and durability, and it’s the norm in contemporary Australian construction – it’s what allows a wall to be sealed and left essentially maintenance-free. It also changes the environmental arithmetic. Cement is carbon-intensive, and every percentage point added to stabilise the mix raises the wall’s embodied carbon. Unstabilised, rammed earth is one of the lowest-impact walls available; heavily stabilised, it can approach the embodied carbon of the conventional masonry it was chosen to better. Published figures vary with cement content and mix, but the direction is consistent, and it’s the first thing worth interrogating in any claim that a rammed earth wall is a low-carbon choice. The label describes the earth; the binder describes the impact.
Unstabilised, rammed earth is one of the lowest-impact walls available. Heavily stabilised, it can approach the embodied carbon of the masonry it was chosen to better.
How does rammed earth perform thermally?
Rammed earth has high thermal mass and low insulation, and conflating the two is the most common error made about the material.
Thermal mass is the capacity to absorb, store and slowly release heat. A dense rammed earth wall does this well: it flattens the daily temperature swing, soaking up heat through the day and releasing it after dark, which keeps interiors steady without mechanical help. In climates with a wide gap between day and night temperatures – much of inland and temperate Australia – that behaviour is genuinely valuable, and it’s why passive solar designs pair rammed earth with north-facing glazing and shading.
Insulation is a different property: resistance to heat passing through the wall at all. Here rammed earth is weak. A solid 300-millimetre wall offers an R-value well below what the National Construction Code requires of an external wall, which means solid rammed earth on its own often can’t meet current energy provisions in cooler climates or where continuous heating or cooling is expected. The response, offered by most Australian rammed earth contractors, is insulated rammed earth: two rammed earth skins built around a central insulating core, commonly around 50 millimetres, which lifts the wall’s R-value while keeping the mass and the finish on both faces. It costs more and thickens the wall, but it’s what makes rammed earth viable across a wider range of climates.
Is rammed earth structural?
Yes, within limits – and this is a genuine point of difference from bio-based insulators like hempcrete or straw, which carry no load and need a separate frame. A stabilised rammed earth wall is load-bearing, generally testing somewhere between about 2 and 4 megapascals in compression, which is ample for single and double-storey construction. Rammed earth walls routinely form the primary structure of houses, and appear in larger public and commercial buildings where their mass and finish are wanted.
What rammed earth can’t do is span or cantilever, and it isn’t a material for slender walls or many storeys. Its structural logic is thickness and compression, which is part of why the walls are as substantial as they are.
How durable is it, and how does it handle fire and water?
A well-detailed rammed earth wall is very durable. Sealed stabilised walls shed weather and, built to an off-form finish, need little or no interior maintenance over their life. Water remains the material’s main adversary, managed through stabilisation, sealing and the hat-and-boots detailing that keeps sustained moisture off the earth.
On fire, rammed earth performs strongly. It’s non-combustible and, in thick sections, offers real bushfire resistance – one reason it recurs in rural and fire-prone Australian projects, where external walls are sometimes built to 600 millimetres specifically for that protection. The density that makes the walls fire-resistant also makes them acoustically dense, which is a quieter benefit that owners tend to notice after the fact.
What does rammed earth cost?
Rammed earth resists a simple number, and the cheap raw material is misleading. The cost sits in labour, formwork, specialist contractors and the coordination the technique demands, not in the earth. One long-established Western Australian builder puts the premium at around 3 per cent over conventional double brick for the wall component, which is at the optimistic end; other contractors describe rammed earth plainly as a high-end, labour-intensive method priced well above standard walling. Both can be true depending on the design – long, simple wall runs are efficient to form and ram, while complex geometry, thick insulated walls and difficult sites push the figure up.
The honest framing is that rammed earth is a considered, premium wall, chosen for its performance and its presence rather than for economy. Where it saves is over time, in reduced heating and cooling and in a wall that doesn’t need replacing, but it isn’t a budget shortcut.
Where does rammed earth work best?
Rammed earth is at its strongest where its properties are actually used. It suits climates with a real diurnal temperature swing, where the thermal mass can do its work, and passive solar designs that position and shade the walls deliberately. It rewards simple, generous wall runs over fussy detailing. And it fits projects where the material’s weight, texture and connection to site are part of the intent, not incidental.
It’s a weaker choice where insulation matters more than mass and the budget won’t stretch to an insulated system, on tight sites with complex geometry, or where the low-carbon case rests on heavy cement stabilisation that quietly undoes it. Naming those conditions is the point: rammed earth is the right answer for specific projects, not a default.
Key considerations for designers, builders and architects
Rammed earth repays early decisions. The mix and its cement content set both the wall’s performance and its carbon profile, so they belong in the conversation at concept stage, not on site. Thermal mass needs a passive solar design around it to pay off, and where insulation is required, an insulated wall system has to be specified early because it changes wall thickness, footings and cost. Services coordination is front-loaded. And because the walls are effectively permanent once rammed, the design has to be resolved before the formwork goes up.
Treated as a considered structural and thermal element – not as a low-carbon shortcut, and not as a decorative finish bolted onto a conventional building – rammed earth is one of the few materials that can be structure, insulation partner, thermal store, fire barrier and finished surface in a single wall. Whether that’s worth its cost and its carbon depends, as it always does, on the specifics of the project and the honesty of the mix.
- Standards Australia, HB 195: The Australian Earth Building Handbook – the primary local reference for earth wall design and construction.
- P. Walker et al., Rammed Earth: Design and Construction Guidelines (BRE) – widely used technical guidance on mixes, stabilisation and detailing.
- Standards New Zealand, NZS 4297 / 4298 / 4299 – engineering, materials and construction standards for earth buildings, referenced across Australasia.
- Australian Building Codes Board, National Construction Code – current thermal performance and R-value provisions for external walls.
- Earth Building Association of Australia (EBAA) – industry body and practitioner resource.
