Cob: two story cob houses - yes

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How Rammed Earth is constructed: 

 

There is more to the construction of earthen homes then just placing ‘ dirt ’ in forms.   One of the primary considerations with rammed earth construction is selecting the right consistency of soil.   It would be ideal to use the on site soil, but this may not be possible.   The Earth must contain the right proportions of aggregate, sand, silt and clay.   For example, clay is usually mixed to 20%.   If too much clay is mixed in the soil, the result will be catastrophic with severe cracking and poor weathering characteristics.   It is also important to keep water contents as close to optimal (8-9%) as possible, as too much water will cause excess lubrication of the soil and weaken the wall.   Soil can also be reinforced by the addition of strengthening agents such as stone aggregates, Portland cement, and hay fibers.   Tests are performed on the proposed soil compositions to ensure all codes are met.   Once the soil source and mixtures have been selected and tested, construction can proceed. 

 

Let us now follow the construction of a typical modern rammed earth house in the varying climatic region of America.   The first step in successful construction, as with any structure, is its foundation.   The foundation acts like the ‘legs’ of the structure, without them the building would just collapse. Typical foundations for rammed earth houses consist of either concrete spread footers or reinforced concrete slabs.   Earth foundations will not hold up to direct contact to a moist environment and therefore it is necessary to use concrete to keep depravation of earth walls minimized.   Reinforcement is typically added to these foundations, dependent upon seismic codes.   Rebar, which is ribbed cylindrical steel, acts as bones do in the body to help strengthen the structure and add rigidity.   The foundation must be able to support the massive weight of the earthen walls.   Failure of the foundation to support the walls will result in severe cracking and failure of the structure. 

 

Once adequate foundations have been constructed, formation of rammed earth walls can proceed.   It is necessary to have quality forms in which the earth is compacted to avoid a catastrophe upon form removal.   One cannot stress enough that the quality of the forms reflects the resultant quality of the finished rammed earth wall.   There are a variety of different forms that various contractors employ in construction, depending upon availability, application, and most importantly cost.   The main characteristic of new forming systems, over that of the ancient forming is speed of assembly and increased volume of earth placement.   Once the formwork system has been decided upon and erected, any fixtures that are typically found within walls (electrical wires, TV and telephone cables), must be placed prior to earth placement or be run externally after wall erection dependent upon desired effects and codes.   

 

Now, commencement of earth placement can begin.   The prior soil selection is mixed to a homogenous consistency and placed in small lifts (levels) in the forms of typically 5 inches.   The soil is then compressed “rammed” into the forms with vibrator hand tampers, which is a labor-intensive process.   The degree of compactness (consolidation) and soil consistency dictate the quality of the finished wall.   Unless a layered appearance is desired, soil should be placed in the forms in as little quantity as possible to avoid forming ‘layering lines’ with each successive layer.   This process is repeated until all of the walls of the structure have been erected.   Wall sections are typically eight to ten foot in length and 8 foot in height.   Once the earth has been placed and compacted, the forms can be removed immediately, which is one of the intrinsic benefits of rammed earth construction.   A cap or header is then constructed upon the top of the earthen walls in preparation for roof placement.   This header can be constructed of either wood or concrete and serves to connect the wall to the roof via reinforcing rods as placed in the foundations.   

 

Next the roof, or second story floor can be placed upon the header.   The roof can be flat or pitched.   Most modern homes in America have sloped roofs, which are constructed out of timber.   These roofs are covered with a watertight membrane and a covering of asphalt, wood, or slate singles is placed upon it.   If a second story is desired, the process of constructing earth walls is repeated from the first floor and then a roof is placed upon it.   Rammed earth homes require no finishing of the walls either on the interior or exterior, unless the homeowner desires it. 

 
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<P class=MsoNormal style="TEXT-ALIGN: justify"><B><I><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt">How 
Rammed Earth is constructed: <?xml:namespace prefix = o ns = 
"urn:schemas-microsoft-com:office:office" /><o:p></o:p></SPAN></I></B></P>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt"> <o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt">There 
is more to the construction of earthen homes then just placing ‘ <I>dirt </I>’ 
in forms. <SPAN style="mso-spacerun: yes">  </SPAN>One of the primary 
considerations with rammed earth construction is selecting the right consistency 
of soil. <SPAN style="mso-spacerun: yes">  </SPAN>It would be ideal to use 
the on site soil, but this may not be possible. <SPAN 
style="mso-spacerun: yes">  </SPAN>The Earth must contain the right 
proportions of aggregate, sand, silt and clay. <SPAN 
style="mso-spacerun: yes">  </SPAN>For example, clay is usually mixed to 
20%. <SPAN style="mso-spacerun: yes">  </SPAN>If too much clay is mixed in 
the soil, the result will be catastrophic with severe cracking and poor 
weathering characteristics. <SPAN style="mso-spacerun: yes">  </SPAN>It is 
also important to keep water contents as close to optimal (8-9%) as possible, as 
too much water will cause excess lubrication of the soil and weaken the wall. 
<SPAN style="mso-spacerun: yes">  </SPAN>Soil can also be reinforced by the 
addition of strengthening agents such as stone aggregates, Portland cement, and 
hay fibers. <SPAN style="mso-spacerun: yes">  </SPAN>Tests are performed on 
the proposed soil compositions to ensure all codes are met. <SPAN 
style="mso-spacerun: yes">  </SPAN>Once the soil source and mixtures have 
been selected and tested, construction can proceed. <o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 0.5in; TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt"> <o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt">Let us 
now follow the construction of a typical modern rammed earth house in the 
varying climatic region of America. <SPAN style="mso-spacerun: yes">  
</SPAN>The first step in successful construction, as with any structure, is its 
foundation. <SPAN style="mso-spacerun: yes">  </SPAN>The foundation acts 
like the ‘legs’ of the structure, without them the building would just collapse. 
Typical foundations for rammed earth houses consist of either concrete spread 
footers or reinforced concrete slabs. <SPAN style="mso-spacerun: yes">  
</SPAN>Earth foundations will not hold up to direct contact to a moist 
environment and therefore it is necessary to use concrete to keep depravation of 
earth walls minimized. <SPAN style="mso-spacerun: yes">  
</SPAN>Reinforcement is typically added to these foundations, dependent upon 
seismic codes. <SPAN style="mso-spacerun: yes">  </SPAN>Rebar, which is 
ribbed cylindrical steel, acts as bones do in the body to help strengthen the 
structure and add rigidity. <SPAN style="mso-spacerun: yes">  </SPAN>The 
foundation must be able to support the massive weight of the earthen walls. 
<SPAN style="mso-spacerun: yes">  </SPAN>Failure of the foundation to 
support the walls will result in severe cracking and failure of the structure. 
<o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 0.5in; TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt"> <o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt">Once 
adequate foundations have been constructed, formation of rammed earth walls can 
proceed. <SPAN style="mso-spacerun: yes">  </SPAN>It is necessary to have 
quality forms in which the earth is compacted to avoid a catastrophe upon form 
removal. <SPAN style="mso-spacerun: yes">  </SPAN>One cannot stress enough 
that the quality of the forms reflects the resultant quality of the finished 
rammed earth wall. <SPAN style="mso-spacerun: yes">  </SPAN>There are a 
variety of different forms that various contractors employ in construction, 
depending upon availability, application, and most importantly cost. <SPAN 
style="mso-spacerun: yes">  </SPAN>The main characteristic of new forming 
systems, over that of the ancient forming is speed of assembly and increased 
volume of earth placement. <SPAN style="mso-spacerun: yes">  </SPAN>Once 
the formwork system has been decided upon and erected, any fixtures that are 
typically found within walls (electrical wires, TV and telephone cables), must 
be placed prior to earth placement or be run externally after wall erection 
dependent upon desired effects and codes. <SPAN style="mso-spacerun: yes">  
</SPAN><o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 0.5in; TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt"> <o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt">Now, 
commencement of earth placement can begin. <SPAN 
style="mso-spacerun: yes">  </SPAN>The prior soil selection is mixed to a 
homogenous consistency and placed in small lifts (levels) in the forms of 
typically 5 inches. <SPAN style="mso-spacerun: yes">  </SPAN>The soil is 
then compressed “rammed” into the forms with vibrator hand tampers, which is a 
labor-intensive process. <SPAN style="mso-spacerun: yes">  </SPAN>The 
degree of compactness (consolidation) and soil consistency dictate the quality 
of the finished wall. <SPAN style="mso-spacerun: yes">  </SPAN>Unless a 
layered appearance is desired, soil should be placed in the forms in as little 
quantity as possible to avoid forming ‘layering lines’ with each successive 
layer. <SPAN style="mso-spacerun: yes">  </SPAN>This process is repeated 
until all of the walls of the structure have been erected. <SPAN 
style="mso-spacerun: yes">  </SPAN>Wall sections are typically eight to ten 
foot in length and 8 foot in height. <SPAN style="mso-spacerun: yes">  
</SPAN>Once the earth has been placed and compacted, the forms can be removed 
immediately, which is one of the intrinsic benefits of rammed earth 
construction. <SPAN style="mso-spacerun: yes">  </SPAN>A cap or header is 
then constructed upon the top of the earthen walls in preparation for roof 
placement. <SPAN style="mso-spacerun: yes">  </SPAN>This header can be 
constructed of either wood or concrete and serves to connect the wall to the 
roof via reinforcing rods as placed in the foundations. <SPAN 
style="mso-spacerun: yes">  </SPAN><o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 0.5in; TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt"> <o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt">Next 
the roof, or second story floor can be placed upon the header. <SPAN 
style="mso-spacerun: yes">  </SPAN>The roof can be flat or pitched. <SPAN 
style="mso-spacerun: yes">  </SPAN>Most modern homes in America have sloped 
roofs, which are constructed out of timber. <SPAN 
style="mso-spacerun: yes">  </SPAN>These roofs are covered with a 
watertight membrane and a covering of asphalt, wood, or slate singles is placed 
upon it. <SPAN style="mso-spacerun: yes">  </SPAN>If a second story is 
desired, the process of constructing earth walls is repeated from the first 
floor and then a roof is placed upon it. <SPAN style="mso-spacerun: yes">  
</SPAN>Rammed earth homes require no finishing of the walls either on the 
interior or exterior, unless the homeowner desires it. <o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-INDENT: 0.5in; TEXT-ALIGN: justify"><SPAN 
style="FONT-SIZE: 14pt; FONT-FAMILY: Century; mso-bidi-font-size: 12.0pt"> <o:p></o:p></SPAN></P></FONT></DIV></BODY></HTML>