Are Rammed-Earth Walls the Next Big Thing?
Rammed earth has natural warmth and beauty, plus the benefits of sustainability, durability and fire-resistance
Rammed earth is a construction technique that has been around for thousands of years and makes up long stretches of the Great Wall of China, the magnificent Kasbahs of Morocco and the enchanting Alhambra in Spain. It is also increasingly seen in contemporary architecture, revived as a sustainable building material for residential housing. The renewed interest in rammed earth walls is due to its thermal mass, strength, durability and visual impressiveness. Rammed-earth houses also have natural warmth and beauty that help tie them to the land and natural environment. Here, we lay the groundwork in this guide to rammed-earth walls in residential architecture.
Stabilised rammed-earth walls
Most modern rammed-earth walls in Australia are stabilised rammed earth. This means a small amount of cement is added to the traditional mixture for increased strength and durability. They are also usually coated with an air-permeable sealer to increase longevity. Stabilised rammed-earth walls are typically 300 millimetres thick for external walls and 200 or 300 millimetres thick for internal walls.
Most modern rammed-earth walls in Australia are stabilised rammed earth. This means a small amount of cement is added to the traditional mixture for increased strength and durability. They are also usually coated with an air-permeable sealer to increase longevity. Stabilised rammed-earth walls are typically 300 millimetres thick for external walls and 200 or 300 millimetres thick for internal walls.
This house on the Mornington Peninsula in Victoria has 300-millimetre-thick stabilised rammed-earth walls, with no finish. The wall acts as a spine in the house, providing a strong visual element and thermal mass, which helps maintain a comfortable stable internal temperature throughout the year.
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Insulated stabilised earth
Rammed earth has limited thermal insulating qualities. However, insulated rammed-earth walls – 400-millimetres-plus thick with a 50-millimetre styrofoam insert – can achieve higher R-value levels and are used more commonly for external walls. R-value is a material’s resistance to conductive heat flow and is measured in terms of its thermal resistance. The higher the R-value, the greater the insulating effectiveness.
Rammed earth has limited thermal insulating qualities. However, insulated rammed-earth walls – 400-millimetres-plus thick with a 50-millimetre styrofoam insert – can achieve higher R-value levels and are used more commonly for external walls. R-value is a material’s resistance to conductive heat flow and is measured in terms of its thermal resistance. The higher the R-value, the greater the insulating effectiveness.
Appearance of rammed-earth walls
The natural materials used in the mixture will determine the colour of rammed-earth walls. Materials are often sourced locally to help buildings blend into their local environments, particularly in rural settings. Rammed-earth walls are typically cream, sand-coloured, peach, light tan or grey through to deep red.
The natural materials used in the mixture will determine the colour of rammed-earth walls. Materials are often sourced locally to help buildings blend into their local environments, particularly in rural settings. Rammed-earth walls are typically cream, sand-coloured, peach, light tan or grey through to deep red.
These 12 rammed-earth apartments have been dug into a sand hill in Western Australia, and the 230-metre-long rammed-earth wall is made from local soil and gravel. The iron-rich and sandy soil was extracted from local clay pans, along with pebbles and gravel quarried from the river bed. The result is a colour palette that blends seamlessly into the landscape.
The ramming process, done layer by layer, can introduce the effect of horizontal or stratified lines that can be used as a feature or removed altogether. Additionally, natural iron-oxide pigments can be introduced to influence the desired colour, and stones can be exposed or incorporated as features or for special effect. The texture and shaping of the formwork will also affect the final result.
Browse more contemporary living rooms here
Browse more contemporary living rooms here
Benefits of rammed-earth walls
- Excellent thermal mass: Rammed-earth walls collect heat from the sun during the day and release that warmth at night. The thickness and density of the material also means the heat or cold penetration of the wall is very slow and the internal temperature of the building remains comparatively stable.
- Fire resistance: Rammed-earth walls are fire resistant as they contain no flammable components. CSIRO tests have demonstrated that a 250-millimetre rammed-earth wall achieves a four-hour fire-resistance rating. This home in Victoria is designed with rammed-earth walls for practical protection in a highly bushfire-prone area.
- Low maintenance: Rammed-earth walls are extremely easy to care for. Once sealed, they shouldn’t need maintaining for at least 10 to 20 years, after which a second coat of sealer may be applied to exposed walls.
Eco Design Principles From the Ground Up
- Natural appeal: The beauty of rammed-earth walls is in its natural qualities, but they can be plastered, rendered or painted over should a change be desired.
- Breathability: Rammed-earth walls are porous by nature. They are non-toxic, non-polluting and ‘breathe’, which can regulate interior humidity and improve indoor air quality, making them suitable for people with respiratory problems.
- Sound insulating: Rammed-earth walls provide excellent sound insulation due to the materials and massing, and the dimming of external noise provides a quieter ambience.
- Moisture-resistance: In general, rammed-earth walls have moderate to good moisture resistance and do not require waterproofing. New water-repellent additives can be added for exposed external walls, but they may inhibit the breathability of the material.
- Durability: Rammed earth is very strong in compression. Their load-bearing abilities usually exceed that of most timber-framed houses, and research in New Zealand indicates that rammed-earth walls perform better under earthquake conditions than brick walls.
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Rammed-earth walls are constructed by ramming an aggregate mixture, including gravel, sand, silt and clay, between flat panels, frames or moulds (otherwise known as formwork). It is an on-site construction method, and removing the formwork reveals the rammed-earth wall.
Traditionally, a wooden pole was used to ram and compress the earth mixture. Today, a mechanical ram is used. Plumbing and electrical points are positioned internally as the walls are constructed.