Rammed Earth: Standards, Strength, Thermal Data and Carbon

Rammed earth is a wall of compacted soil built up in layers inside temporary formwork. It is specified for load-bearing and non-load-bearing walls, for prefabricated wall panels and, in cement-stabilised form, for exterior walls.^[10][11][3] The questions that matter are whether the mix is stabilised, which code the wall is designed under, and what the strength, thermal and moisture figures actually refer to.

This guide sets out what the documents we read say. For earth finishes see clay plaster, and for lime renders see lime plaster, rather than a repeat of them here.

What is rammed earth, and how do stabilised and unstabilised walls differ?

Soil mix and layering

A 2026 systematic review describes rammed earth as compacted moist soil (clay, silt, sand and a small share of gravel) in temporary formwork.^[15] The New Mexico code adds limits for the soil: no rock over 1½ inches, no clay lumps over ½ inch, free of organic matter, and no more than two percent soluble salts.^[3] An Australian specification for a proprietary stabilised-earth formwork system limits organic content to under 2 % and material finer than 0.075 mm to under 20 %.^[4]

Layer thicknesses differ by document. BauNetz Wissen, a German architecture information portal, describes earth-moist soil poured in layers 10–15 cm high into a pressure-resistant formwork and compacted with rammers; it adds that there is no setting time, so the formwork can be stripped at once, but loads should only be applied once the wall is fully dry.^[10] The Australian specification allows layers of at most 200 mm, compacted within two hours of blending, with forms left in place for 12 hours;^[4] the New Mexico code allows lifts of at most eight inches and requires cement-stabilised soil to be placed within 60 minutes of preparation.^[3] The architects of the Nk'Mip wall describe 150–200 mm lifts compressed with pneumatic tampers.^[13]

Stabilised versus unstabilised

The New Mexico code defines stabilised rammed earth as soil that passes the ASTM D1633-00 wet strength test or contains a minimum of six percent Portland cement by weight; unstabilised soil is the opposite, and its exterior must be protected with an approved stucco system or another method the building official accepts. It also lets fully stabilised walls be left unprotected from the elements.^[3] GreenSpec, a UK specification resource, says cement is the most common stabiliser and typically makes up 6 or 7 % of the mix by volume, and says that adding cement (high embodied energy) can compromise the material's environmental credentials.^[1] The Australian specification gives 6 % minimum to 10 % maximum cement by volume for gravels, laterite soils and soil blends, and at least 7 % for crushed limestone or sandstone, recycled rubble and reinforced walls, each fixed by a mix design and strength test.^[4] The bases differ (weight in one document, volume in the others) and we do not convert between them.

Durability is a central concern. The abstract of Arrigoni and co-authors (2019) states that poor resistance to weathering compromises the durability and acceptance of earthen buildings, and tests fly ash and calcium carbide residue as waste-based stabilisers.^[21] Windstorm and Schmidt's peer-reviewed report on contemporary North American practice (abstract read) describes modern stabilised rammed earth as adding steel reinforcement and rigid insulation, designed by licensed structural engineers under concrete or masonry codes.^[20]

What do building codes and standards say about rammed earth?

We opened catalogue pages and codes, not paid standards, so each entry below says what we read.

• New Zealand. The CodeHub page for NZS 4297:1998 (valid from 1/10/1998 as printed) gives a scope of unfired earthen wall materials defined as adobe, pressed brick, poured earth or rammed earth, with or without chemical stabilisation; materials must comply with NZS 4298 and construction may not exceed 6.5 m in height.^[5] The Earth Building Association of New Zealand lists revised 2024 editions of NZS 4297, 4298 and 4299, free to download from Standards New Zealand.^[6] We did not open the 2024 texts or NZS 4299.
• United States. New Mexico's Earthen Building Materials Code (14.7.4 NMAC, 2021 edition, amended 14 July 2023) defines rammed earth and sets, for example, a limit of two stories, a minimum of 18 inches for exterior walls (with an exception for solar mass walls), 300 psi minimum compressive strength for soil samples, and 200 psi after seven days for stabilised soil.^[3] ASTM's catalogue page for E2392/E2392M-10 (2016), titled as a standard guide for design of earthen wall building systems, is marked historical and lists E2392/E2392M-24 as the active version.^[7] We did not read either edition of the guide.
• Germany. A presentation by the Industrieverband Lehmbaustoffe (19 March 2025) lists DIN 18945 (earth bricks), 18946 (masonry mortar), 18947 (plaster) and 18948 (boards), and DIN 18940:2023-06 for load-bearing earth-brick masonry; for on-site rammed earth and straw clay it names the Lehmbau Regeln of the Dachverband Lehm.^[8] BauNetz Wissen lists the DIN 18945–18947 editions as 2018-12 where the presentation lists 2024; we show both and do not decide.^[9] Lücking's prefabricated-wall sheet states that design and production follow the Lehmbau Regeln as introduced by the building authorities.^[11] We did not open the DIN texts or the Lehmbau Regeln.
• Australia. We could not open the catalogue entry for the Australian Earth Building Handbook (HB 195). The Australian specification we read names AS 1289 soil tests, AS 1141.51-1996 for unconfined compressive strength and CSIRO Bulletin 5 for soil evaluation.^[4]
• United Kingdom. GreenSpec states that there are no UK codes of practice for rammed earth and that fitness under the Building Regulations is judged by sampling, laboratory testing or precedent.^[1] NBS's 2013 programme page says earth building is relatively rare in the UK and names walls at the Eden Project and the Centre for Alternative Technology.^[2] We did not find a Historic England document, and the link to the Bath review of rammed earth construction redirected to the university home page.

How strong is rammed earth?

Strength depends on the soil, the stabiliser and the test. Bilad and Ikharrazne's 2026 open-access systematic review of 52 publications reports compressive strength of 1 to 2.75 MPa for unstabilised and 1.2 to 9.40 MPa for stabilised rammed earth, tensile strength of 0.16 to 0.38 MPa for unstabilised, and shear strength of 7 to 10 % of compressive strength.^[15] GreenSpec gives a maximum of 1 MPa for unstabilised and about 10 MPa for stabilised.^[1] The two documents differ, and both are summaries, not test reports.

Specifications set minimums rather than typical values: 300 psi for soil samples in New Mexico, with 200 psi after seven days for stabilised soil,^[3] and a characteristic adjusted compressive strength of at least 2.5 MPa in the Australian specification.^[4] Lücking's prefabricated wall sheet states compressive strength class 3 without defining the class on the sheet; we have not read the class definition.^[11] Moisture also governs loading: in the Detmold research project, laboratory tests found that full loading of the earth walls should wait until they reach equilibrium moisture, and a drying simulation gave about 1.5 years on site to reach the 1.1 to 1.9 mass percent required.^[14]

How does rammed earth perform thermally, with moisture and in fire?

Thermal conductivity and thermal mass

The review's Table 11 collects values from other studies: unstabilised samples between 0.46 and 1.6 W/mK in its rows that give ranges (densities 1,700 to 2,400 kg/m³), further single unstabilised values from 0.48 to 1.48, one unstabilised soil at 0.64 and the same soil with 25 % fly ash at 0.52, and soil with 10 % cement at 0.80 and with 7.5 % rice husk ash added at 0.65 W/mK.^[15] It adds that conductivity depends on moisture content, grading, stabilisers and additives.^[15] A Romanian study of 12 compacted clay soils measured 0.523 to 1.209 W/mK at 1,490 to 2,150 kg/m³ and then modelled heat flow through simulated walls.^[16] The review credits rammed earth with high thermal mass,^[15] while GreenSpec says its thermal resistance is poor, so external walls need additional insulation, and that the extent of its thermal mass benefit is still being quantified.^[1]

Insulated assemblies are the response in several documents: the Nk'Mip wall uses two 250 mm earth leaves with 100 mm of polyisocyanurate between them, which its authors give as about R33,^[13] and Windstorm and Schmidt describe rigid insulation placed to form a dense inner layer thermally separated from the exterior.^[20]

Moisture, sound and fire

• The DBU research report on the Detmold museum measured µ of 9 and 13.3 on two batches of a ready-mixed rammed earth, partly within the guide values of 5 to 10 in the Lehmbau Regeln, and a sorption isotherm lower than the database values it compared with. Its room-climate simulations showed smaller humidity swings with rammed earth than with a concrete variant.^[14]
• Hall and Allinson's peer-reviewed study of three stabilised mixes (abstract read) found that higher porosity went with lower volumetric heat capacity and higher sorptivity and vapour permeance.^[17] A later peer-reviewed study is titled "Reduction of rammed earth's hygroscopic performance under stabilisation"; we read only its title.^[22]
• The same DBU report measured weighted sound absorption coefficients αw of 0.35 and 0.40 on specially built rammed earth walls with two ready mixes, in the reverberation room to DIN EN ISO 354, placing them in absorber class D.^[14]
• GreenSpec says rammed earth can be classed as non-combustible and that a 300 mm wall gives at least 90 minutes of fire resistance.^[1] The Industrieverband presentation states earth is generally A1 under DIN 4102-4 and shows a Detmold slide listing proof of REI 90 without saying which wall it refers to.^[8] We opened no test report.

How much carbon is in rammed earth?

We did not find an EPD for a rammed earth wall, so there is no declared A1–A3 figure to quote. The peer-reviewed literature gives comparisons.

• Arrigoni and co-authors (2017) write that traditional rammed earth is deemed environmentally friendly but its modern stabilised counterpart is not, that durability tests are far less common than strength tests, and that inflated strengths lead to excessive use of stabilisers. Using attributional and consequential LCA and cumulative energy demand on several mixes, they report that durable stabilised mixes are possible without the cost of using environmentally expensive stabilisers.^[18]
• Meek and co-authors (2021) assessed cradle-to-gate emissions for hypothetical building envelopes in Perth and Kalgoorlie, Western Australia. They report that mixes with recycled crushed brick and concrete plus slag, fly ash or silica fume cut emissions per vertical square metre of wall by 73 % against cavity brick and 57 % against brick veneer, whereas rammed earth with cement saved 15 % against brick veneer.^[19]
• GreenSpec says adding cement can compromise the material's environmental credentials, though this might be balanced out by the protection and maintenance that unstabilised walls need.^[1]

These are modelled results for specific mixes and regions, read from abstracts, and are not product declarations. The Detmold report's building-level life-cycle work covers the whole building, not a rammed earth product, so we do not quote it as a material figure.^[14]

Where is rammed earth used?

Rammed earth in use: two documented projects

Both projects are described in the sources named, and we state only what those sources say.

• Entrance and exhibition building, LWL Open-Air Museum, Detmold (Germany), ACMS Architekten. A trade-association slide lists about 600 m³ (1,200 m², about 1,200 t) of rammed earth, of which 820 m² are 0.60 m thick walls built in situ and 360 m² are 0.15 m thick prefabricated elements.^[8] The DBU research report, which lists ACMS Architekten as a project partner and refers to a 2018 design competition, describes 60 cm thick, up to eight metre high walls of mono-material rammed earth built both traditionally and as large prefabricated elements made on site; it says the earth came from a Detmold supplier, mainly from a construction pit in Blomberg.^[14] We did not read a source for the completion year.
• Nk'Mip Desert Cultural Centre, Osoyoos, British Columbia (Canada), Hotson Bakker Boniface Haden Architects + Urbanistes, built by Terra Firma Builders. According to the architects' article in Canadian Architect (1 March 2007), the wall is about 80 m long and 5.5 m high, with a total assembly 600 mm thick: two 250 mm rammed earth leaves around 100 mm of polyisocyanurate insulation, heavily reinforced, in forms 600 mm wide. The mix is a sand and soil blend with Portland cement and 5–10 % water, with concrete colourants; the article does not state the cement percentage or the construction year.^[13]

Suppliers whose documents we read

Frequently asked questions about rammed earth

The bottom line on rammed earth

Rammed earth is a family of mixes, not one material: whether it is stabilised, which code applies, and how the wall is insulated change the figures that matter. Codes and project specifications hold the minimum strength and cement requirements, peer-reviewed papers hold the comparative carbon and hygrothermal findings, and a manufacturer's sheet holds only that product's values. We found no EPD and no independent emissions or fire report for a rammed earth wall.

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