Nine recommended reads on earth and straw
Date published

15 January 2021

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Nine recommended reads on earth and straw

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Date published

15 January 2021

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James Norman, Associate Professor of Sustainable Design at the University of Bristol, shares his favourite guidance documents on earth and straw.

Our clients are becoming more aware of the need for low-carbon designs. This means that there will be an increasing focus on the use of biogenic (natural) materials within structural engineering.

This suggested reading list is a must for any engineer who wants to know more about earth and straw. James has also put together a suggested reading list on the use of timber and bamboo with David Trujillo.


Earth as a structural material


Earth is an ancient material. Dug from the ground and compacted into layers, it can create a beautiful rustic environment. Earth’s sustainability comes from the way that it affects the internal air quality and its low embodied energy. If we avoid stabilisers such as cement, it can also be put back into the ground at the end of use.

However, if we are unable to use site won material and start importing it, its carbon footprint goes up. If we add stabilisers it goes up further and can no longer be put back into the ground.

We therefore need a good understanding of the available earth on site and its suitability for structural purposes. As engineers we shouldn’t just choose to build from rammed earth, we should let the site guide us.


Recommended reading on earth

WALKER ET AL., (2005). Rammed Earth: Design and Construction Guidelines. BRE

This is the most useful book on the design and detail of rammed earth. Be aware that it does not cover all items. Engineers will need to apply a degree of judgement to enable them to carry out full design calculations. Print copy available for loan by post or in person to IStructE members


 

JAQUIN PJ. And AUGARDE C. (2011) Earth Building: History, Science and Conservation. BRE

This book covers the restoration and repair of historic rammed earth structures. It is a very useful guide if you are working on refurbishment projects but may be less useful for design and detail of new buildings. It is worth noting that rammed earth can be scoured by water. Because of this you may want to consider providing details to the client on maintaining and repairing earth structures.

KING B. (1996) Buildings of Earth and Straw, Green Building Press

Bruce King writes funny and philosophical guides to design unlike anything else out there. I would highly recommend his book for that reason alone. However, for rammed earth he approaches it as low grade concrete, which is less helpful for unstabilised rammed earth. Print copy available for loan by post or in person to IStructE members.

Codes of practice

Australia, New Zealand and India all have codes of practice that cover the use of rammed earth. The Australian codes are currently being updated and are due for release mid-2021.

Straw as a structural material


Straw is available as a construction material across the UK. It has many benefits:
  • Its insulating properties
  • It is completely renewable
  • It is a waste product which is often ploughed back into the ground
When designing with straw we need to consider whether it is an infill material (normally with timber frame) or loadbearing. Whilst the below references offer insights into both, designing load bearing in the UK does have its challenges.

For first time straw designers, infill panels are more straight forward and have been covered in more detail in the references below.


Recommended reading on straw



 

Californian Building Code, Appendix S: Strawbale Construction of the International Residential Code Commentary

The Californian Building Code is the most comprehensive design guide for straw bale construction. It relies on a number of empirical tables and has limited scientific explanation. The simple assumption is that the straw itself is not load bearing but instead restrains the render (or plaster in the code) which carries the vertical load. Significant care should be taken applying this code as it is written within the context of US codes. This means it cannot be simply slotted in to a Eurocode design methodology.

Straw Bale Building Details: An Illustrated Guide for Design and Construction (2019), California Straw Building Association (CASBA)

This book is published to provide further information to support the Californian Building Code. It contains a large amount of detail and covers a useful spectrum of different considerations. However, there is not significant structural design information. Available as an elibrary loan to IStructE members.

Jones B. (2015) Building with Straw Bales: A practical manual for self-builders and architects, Green Books.

Includes lots of information around detailing and construction of straw construction. It contains very little information on the structural capacity. It’s useful if you are looking to design and detail non-structural straw infill panels. Available as an elibrary loan to IStructE members.

Pelly R. and Mander T. “The Nucleus building, Hayesfield Girls’ School Bath: achieving low embodied carbon using renewable materials”, The Structural Engineer, pp 16-22, October 2014.

This is an interesting case study using modular strawbale construction. It also looks at the embodied energy and in use energy savings achievable with this form of construction.

Thomson A. and Pete Walker P. (2014), Durability characteristics of straw bales in building envelopes, Construction and Building Materials vol 68 pp135–141.

A more detailed look at the durability of straw.

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