building
project intro 
Building with Earth. A highly informative book on rammed earth. (click for larger image)  the foundation design (click for detailed image) |
Preface: I want to express my thanks to Scott Hinds and Eric Berger from the Chemical Lime Co. They have both been incredibly generous with their time, knowledge and direct assistance during my research into lime plaster and lime-stabilisation.
The building will be supported by a rubble trench foundation capped with a lime-stabilised rammed earth stem wall. This system dramatically reduces the amount of energy required to construct the foundations and eliminates the use of cement.
The building will be supported by a rubble trench foundation capped with a lime-stabilised rammed earth stem wall. This system dramatically reduces the amount of energy required to construct the foundations and eliminates the use of cement.
Ethnic foundations: the wood pilings supporting houses in the old 'water village' in Bandar Seri Bagawan, Brunei. The posts are replaced every seven years on average.
The Rubble Trench...
As the name implies, a trench is dug down to undisturbed earth or rock and is filled to grade with rubble (see diagram on left).
This system combines two essential functions. It provides solid but resilient support for the building - capable of distributing loads evenly while also absorbing any settling and seismic movement. Simultaneously it acts as a drain, channeling water away from the foundation and eliminating the risk of frost heave that can be a destructive force in cold climates.
The trench will be slightly wider than the width of the walls above thus providing a 'french drain' to catch any water that might otherwise collect at the base of the walls. The rubble typically is crushed jagged rock ranging in size from 1 - 4 inches but can be made up of recycled concrete or other aggregates. Jagged rock is best as the rough edges tend to bond better when compessed, making it more stable. The bed of the trench is sloped slightly with perforated drain pipe installed in the bottom to channel water away from the building.
The houses of Parliament in London are founded on a rubble trench, and the architect Frank Lloyd Wright used them in many of his iconic buildings, such as the Johnson Wax Administration Building in Racine, Wisconsin, and his own home, Taliesin, in Spring Green, Wisconsin.
The Stem Wall...
On top of the rubble trench will be a stem wall that rises between 10 to 24 inches above grade and on which rests the supporting structure and walls. The rubble trench protects the stem wall from contact with ground water while the stem wall lifts the building off the ground and isolates it from rain splash.
Consequently there is very little chance of moisture penetrating the walls due to capillary action. This eliminates the need for a vapour barrier at the bottom of the walls. Low evergreen shrubs or grasses planted around the building can further protect the walls from splashing.
The stem wall will be constructed using two techniques - lime stabilisation and rammed earth - that have been used for - and lasted - thousands of years.
For example: sections of the great wall of China were constructed with rammed earth over 2000 years ago; the Romans perfected the use of lime to create waterproof aquaducts that are 4000 years old and still hold water; and modern road construction relies heavily on lime stabilised soil to create the necessary strength and resilience to support heavy traffic loads.
Lime Stabilisation...
The addition of quicklime or hydrated lime to soil in specific ratios causes a chemical reaction which dries, strengthens and stabilises the soil. This is particularly useful with soils that are clay-rich and therefore prone to expansion when they get wet. The lime neutralises this expansion.
In the chemical reaction the aluminum and magnesium sulphates in the clay, as well as silicates (natural pozzolans) are broken down and combine with calcium in the lime to create a very stable, strong bond.
Most soils contain enough clay to benefit from lime stabilisation, however it should be tested to ensure the right amount of lime is added to create the optimum strength. (see 'Soil testing' below)
Rammed Earth...
In many parts of the world rammed earth walls are made without stabilisation and perform very effectively. However, in a wet and cold environment the addition of lime (or cement) provides a valuable degree of strength and durability.
Rammed earth stabilised with cement is being used extensively in Australia and other countries to build the walls of houses. However, my research leads me to believe that using lime may well be better than cement. Although it may not have the same maximum strength and does not set as quickly, it does become very strong yet retains a degree of flexibility that cement lacks. The lime also reabsorbs CO2 as it sets, reversing some of its greenhouse gas emissions.
Rammed earth has excellent 'thermal mass' (the ability to store and slowly release heat) but does not have a high r-value (insulation). Consequently, we also will be experimenting with ways to use natural materials such as Pumice and Perlite to increase its insulative properties.
Furthermore, based on extensive research done in Germany, samples will be tested for durability with additive such as Linseed oil and cow manure which have both been shown to have a pronounced benefit.
Rammed earth walls are created by erecting panels - or 'forms' - to create the shape of the wall. Between these forms a layer - or 'lift' - of soil is poured. Each lifts is usual about 6 - 8 inches thick. The soil is lightly tamped and then left to 'mellow' for a period of about 24 hours during which the lime begins to react with the soil. It is then compressed - or 'rammed' - down by the use of either pneumatic or manual tampers until it is reduced to about half its original thickness.
Once a layer has been compressed, the next lift is poured, mellowed and rammed until the wall reaches the desired height. Depending on the final height of the walls, the forms may need to be raised periodically as the wall grows.
Although metal rebar has recently been shown to work quite effectively in rammed earth I hope to avoid using it for various reasons: the production of steel is a major contributor to GHG emissions; and, as has been shown in conventional concrete construction, rebar is subject to rusting which can eventually cause serious damages to the structure. To increase tensile strength we probably will be using horse hair (of which we have an abundant local supply).
An added benefit of using rammed earth is that, in many cases, the soil from the site can be used to build with. This not only eliminates a significant cost of materials, but also the carbon footprint of transportation!
Soil testing...
An important part of using these materials and techniques will be to conduct a series of different tests.
The first of these will be a soil test to ASTM 6276 specifications (the Eades and Grim pH test). Different percentages of lime are added to the soil in order to determine the point at which the pH level of the sample levels out - typically pH12. This establishes the optimum amount of lime required to ensure that the necessary chemical reaction takes place completely. Unless the soil is particularly acidic, this is usually between four and six percent lime by dry weight.
Testing of my soil by Eric Berger at the Chemical Lime Co in Texas has shown that I will need 4% lime for effective stabilisation.
The second is the 'Proctor Curve' test which establishes the optimum moisture content of the soil for a given level of compaction. Although I cannot claim to fully understand the significance of this test, I can understand that too much water will make it harder to compress the soil, and too little may slow down the chemical reaction. For lime-stabilised rammed earth construction, the best ratio of moisture is about 3 - 10% above the 'optimum' level as determined by the Proctor Curve test.
The third test is to make samples of rammed earth for compression testing. This will establish the strength of the stabilised soil to ensure that it will bear the weight of the walls and roof. Because pumice and perlite are not as solid as conventional aggregates they will reduce the strength of the samples. Consequently, numerous samples will be tested to determine the best balance between compressive strength and level of insulation.
The minimum strength required will be determined by my structural engineer.
As the name implies, a trench is dug down to undisturbed earth or rock and is filled to grade with rubble (see diagram on left).
This system combines two essential functions. It provides solid but resilient support for the building - capable of distributing loads evenly while also absorbing any settling and seismic movement. Simultaneously it acts as a drain, channeling water away from the foundation and eliminating the risk of frost heave that can be a destructive force in cold climates.
The trench will be slightly wider than the width of the walls above thus providing a 'french drain' to catch any water that might otherwise collect at the base of the walls. The rubble typically is crushed jagged rock ranging in size from 1 - 4 inches but can be made up of recycled concrete or other aggregates. Jagged rock is best as the rough edges tend to bond better when compessed, making it more stable. The bed of the trench is sloped slightly with perforated drain pipe installed in the bottom to channel water away from the building.
The houses of Parliament in London are founded on a rubble trench, and the architect Frank Lloyd Wright used them in many of his iconic buildings, such as the Johnson Wax Administration Building in Racine, Wisconsin, and his own home, Taliesin, in Spring Green, Wisconsin.
The Stem Wall...
On top of the rubble trench will be a stem wall that rises between 10 to 24 inches above grade and on which rests the supporting structure and walls. The rubble trench protects the stem wall from contact with ground water while the stem wall lifts the building off the ground and isolates it from rain splash.
Consequently there is very little chance of moisture penetrating the walls due to capillary action. This eliminates the need for a vapour barrier at the bottom of the walls. Low evergreen shrubs or grasses planted around the building can further protect the walls from splashing.
The stem wall will be constructed using two techniques - lime stabilisation and rammed earth - that have been used for - and lasted - thousands of years.
For example: sections of the great wall of China were constructed with rammed earth over 2000 years ago; the Romans perfected the use of lime to create waterproof aquaducts that are 4000 years old and still hold water; and modern road construction relies heavily on lime stabilised soil to create the necessary strength and resilience to support heavy traffic loads.
Lime Stabilisation...
The addition of quicklime or hydrated lime to soil in specific ratios causes a chemical reaction which dries, strengthens and stabilises the soil. This is particularly useful with soils that are clay-rich and therefore prone to expansion when they get wet. The lime neutralises this expansion.
In the chemical reaction the aluminum and magnesium sulphates in the clay, as well as silicates (natural pozzolans) are broken down and combine with calcium in the lime to create a very stable, strong bond.
Most soils contain enough clay to benefit from lime stabilisation, however it should be tested to ensure the right amount of lime is added to create the optimum strength. (see 'Soil testing' below)
Rammed Earth...
In many parts of the world rammed earth walls are made without stabilisation and perform very effectively. However, in a wet and cold environment the addition of lime (or cement) provides a valuable degree of strength and durability.
Rammed earth stabilised with cement is being used extensively in Australia and other countries to build the walls of houses. However, my research leads me to believe that using lime may well be better than cement. Although it may not have the same maximum strength and does not set as quickly, it does become very strong yet retains a degree of flexibility that cement lacks. The lime also reabsorbs CO2 as it sets, reversing some of its greenhouse gas emissions.
Rammed earth has excellent 'thermal mass' (the ability to store and slowly release heat) but does not have a high r-value (insulation). Consequently, we also will be experimenting with ways to use natural materials such as Pumice and Perlite to increase its insulative properties.
Furthermore, based on extensive research done in Germany, samples will be tested for durability with additive such as Linseed oil and cow manure which have both been shown to have a pronounced benefit.
Rammed earth walls are created by erecting panels - or 'forms' - to create the shape of the wall. Between these forms a layer - or 'lift' - of soil is poured. Each lifts is usual about 6 - 8 inches thick. The soil is lightly tamped and then left to 'mellow' for a period of about 24 hours during which the lime begins to react with the soil. It is then compressed - or 'rammed' - down by the use of either pneumatic or manual tampers until it is reduced to about half its original thickness.
Once a layer has been compressed, the next lift is poured, mellowed and rammed until the wall reaches the desired height. Depending on the final height of the walls, the forms may need to be raised periodically as the wall grows.
Although metal rebar has recently been shown to work quite effectively in rammed earth I hope to avoid using it for various reasons: the production of steel is a major contributor to GHG emissions; and, as has been shown in conventional concrete construction, rebar is subject to rusting which can eventually cause serious damages to the structure. To increase tensile strength we probably will be using horse hair (of which we have an abundant local supply).
An added benefit of using rammed earth is that, in many cases, the soil from the site can be used to build with. This not only eliminates a significant cost of materials, but also the carbon footprint of transportation!
Soil testing...
An important part of using these materials and techniques will be to conduct a series of different tests.
The first of these will be a soil test to ASTM 6276 specifications (the Eades and Grim pH test). Different percentages of lime are added to the soil in order to determine the point at which the pH level of the sample levels out - typically pH12. This establishes the optimum amount of lime required to ensure that the necessary chemical reaction takes place completely. Unless the soil is particularly acidic, this is usually between four and six percent lime by dry weight.
Testing of my soil by Eric Berger at the Chemical Lime Co in Texas has shown that I will need 4% lime for effective stabilisation.
The second is the 'Proctor Curve' test which establishes the optimum moisture content of the soil for a given level of compaction. Although I cannot claim to fully understand the significance of this test, I can understand that too much water will make it harder to compress the soil, and too little may slow down the chemical reaction. For lime-stabilised rammed earth construction, the best ratio of moisture is about 3 - 10% above the 'optimum' level as determined by the Proctor Curve test.
The third test is to make samples of rammed earth for compression testing. This will establish the strength of the stabilised soil to ensure that it will bear the weight of the walls and roof. Because pumice and perlite are not as solid as conventional aggregates they will reduce the strength of the samples. Consequently, numerous samples will be tested to determine the best balance between compressive strength and level of insulation.
The minimum strength required will be determined by my structural engineer.
Links... (hover over links for info)
The Living Building Challenge
Fotoprint
John Gower - Gower design group
Chelsey Braham - C D B Design
Earth Futures
BCSEA
SIPDistribution.ca
Chemicallime.com
Perlite.com
Strawbale.com
HomesteadHouse.ca
Eco-Sense.ca
Building Limes Forum
Straw bale fire test movie
Straw bale earthquake test movie
Susanne Dannenberg - visual artist
Goodshepherdwool.com
Elke Cole