IN-Review: "The Hempcrete Book: Designing and Building with hemp-lime"

IN-Review: “The Hempcrete Book: Designing and Building with hemp-lime”

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The use of concrete has been part of our surroundings for a long time because of its great resistance, but at the same time, throwing enormous quantities of Carbon Dioxide (CO2) to the environment when its cement compound is being manufactured. How can natural resources functioning as construction materials help reduce these carbon emissions? The use of permaculture, the application of organic materials, is an alternative for Designers, Architects and Landscape Architects, that will soon become an important method for sustainable design as it is already for a minor group. Although technology and digital design can surprise us most of the time, it is technology itself that will be accompanying organic materials, in order the make the perfect digi-symbiosis of our future cities.

This is what using Hemp means, as written in a previous article, the properties and applications of this natural resource, are very impressive and here is a book exposing its use for construction mixed with lime-cement.

This beautiful book by William Stanwix and Alex Sparrow, titled The Hempcrete Book: Designing and Building with Hemp-lime, is a serious guide on how to build with hempcrete, from the mix to the finished building without missing a detail. Stanwix and Sparrow are current partners of the company Hemp-Lime Construct in UK, where building with Hemp is part of its history and is traditionally used for historical preservation.

Hemp is the Industrial processing of the plant called Cannabis Sativa in this case used as construction material for natural building, making sustainable and low-carbon structures.

The book is divided into three (3) parts, each one including a case study titled “focus on self-buid”
Part 1: Principles of Building with Hemprete.
Part 2: Hempcrete Construction
Part 3: Designing a Hempcrete Building.

Part 1: Principles of Building with Hempcrete.

This section provides information of the plant, it’s origins, history of its uses in the UK and how it is processed for its further use on buildings. Explanations on why this plant is so beneficial as a construction material is also described, specifying the differences between all the Cannabis plant types, and why the Sativa version is the correct one for this particular use. In the case of aggregates to Hempcrete, Lime, which is one of the main ingredients of the binders for Hempcrete, is also introduced and defined by the authors themselves as “building lime, a product made from naturally occurring and plentiful sources of calcium carbonate, it has been used as a building material through-out history.” All types of lime are also described as part of the understanding of the properties behind Hempcrete. Why lime?, some might be asking, why not use cement for easier access?

“Lime for building is produced from calcium carbonate (CaCO3), found naturally in quarried limestone, chalk, coral rocks or shell. The raw materials are burnt in a kiln, causing a chemical change to occur: carbon dioxide (CO2) is given off, leaving behind calcium oxide (CaO)- a substance known as ‘quicklime'”.

Lime and cement are not to be confused as being materials with similar characteristics. For starters, lime doesn’t require so much heating as concrete does, making the latter require much more energy and much more carbon emissions. The next chart makes a clear comparison between materials performances.

Now that the clear reason for which lime is best used as a grinder material, we could ask: Why did we stopped using Lime for our concrete mix? An issue of cost might be a reason of change, another might be the disappearance of processing machines.
Part of what is also included in this chapter, is what we can call a guideline, explaining how to start working with Hempcrete, how to process everything from the crop harvesting, to the consistency of the mix. How to pour it or shot-crete it, how to use it as cast in place or build blocks with the mix, very similar to our traditional concrete, but with upgraded properties that create breathable walls.

HandPlacedHemp_3=credit-alex-sparrow

Hand-placed Hempcrete. Image by Alex Sparrow

In terms of sustainability, the use of living materials for construction is a key factor in the development of carbon negative buildings, a topic impregnated inside this beautiful book. Because plants are carbon sequesters by nature, using it inside our construction materials, represent an important aid at reducing carbon emissions from building construction and material production. Clearly, hempcrete buildings are much more possible in the UK because there is no prohibition for cultivating Cannabis. In the USA, there are plenty of limitations and just a few states are able to plant Cannabis for medicinal purposes.

Part 2: Hempcrete Construction

This is one of the most important parts of the book, where performance and properties of hempcrete, are described. A bit of science of the materials here explained, as well as references of other books that lead to their research up to the date of writing the book. Just to mention one of them, (because I love books about materials), the book “Bio-aggregate-Based Building Materials: Applications to Hemp Concretes” , by Sofiane Amziane and Laurent Arnaud, describes much of these properties in depth, and as recommended by the authors, this one should be considered if there is much interest in building with Bio-aggregates in the future.

Now, back to the Hempcrete book, another important part of building with hemp is learning about its structural factor. Hempcrete by itself is not a load bearing material, reason for which it is important to design its structural frames accordingly; the only detail here, is that it must have a timber frame and not steel frames because of the use of lime in the mix. (Any steel materials might be able to be used for structure if possible and other wood connections but always protected from hempcrete). In terms of the mix, as you can see below, can be performed with a pan mixer or a bell mixer, distinctions explicitly described on the book for perfect comprehension.

In addition, Hempcrete’s applications cover roof, walls and floors, the whole building just exactly as you we typically do with concrete itself but with added properties. Hempcrete be can sprayed-on to the wall boards, can be hand placed and rammed, can be used as masonry blocks and also as Panel system for higher performance walls. If this material can achieve all these applications and further provide a thermal wall, roof or floor, I vote for this to be used worldwide.

Part 3: Designing a Hempcrete Building.

This third part of the book contains more detailed information regarding construction documentation and how to understand the behaviour of hempcrete with all other elements in construction. Through two chapters about “Design Fundamentals” and “Indicative Detailing”, this guide for hempcrete construction, is the perfect ABC for this innovative sustainable material.

A quick detail that comprise the material in relation to other typical elements in construction such as electrical outlets or any other metals, is carefully presented here. For instance, the use of hempcrete represents an increased amount of alkaline for metals in the project; for island or coastal construction this might be even more significant. Metals cannot come into contact to hempcrete, reason for which it is recommended to at use least galvanize the steels, but scratches should be avoided. Stainless steel, which is a combination of chromium and oxygen (or chromium oxide), turns steel into a self healing and anti-corrosion material, making it suitable for hempcrete buildings. (If in any case, the hempcrete building is to be constructed with metal studs, these will have to be encased and hermetically sealed to forbid the contact with the hempcrete walls and as suggested by the authors, it should be perfomed at your own risk as it will somehow end up corroding the galvanized steel studs.)

In addition to these material characteristics and intrinsic relationships, the authors filled the book with amazing detailed sketches with clear explanations of these hempcrete walls, its essential construction and how to work with openings, in detailed sections as the following:

How vapor permeability works on a hempcrete wall. Image by: William Stanwix

How vapor permeability works on a hempcrete wall. Image by: William Stanwix

Hempcrete_Text to Page 285 AD 21.4.14.indd

If you are interested in learning more about using living materials for construction and how to use hempcrete for your upcoming projects or tests, I encourage you to get this book today. It is by far, the most detailed version on the market and completely easy to understand. You can find this and other interesting books at INmatteria’s book store.

Also, to get a live overview of what hempcrete construction is about, spend a moment watching this video from Hempcrete Technology:


This article has been made possible, thanks to Green Books UK’s book submission, in coordination with the authors: William Stanwix and Alex Sparrow, which are among the foremost experts on building and renovating with hempcrete.

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References:

http://www.ukhempcrete.com/hempcrete-book


Note to reader:
Editions made on February 18, 2017 on those paragraphs mentioning the use of stainless steel or wood studs only. There are no assumptions on this book review, every detail was extracted from the book The Hempcrete Book: Designing and Building with hemp-lime”. Please take in consideration the high alkalinity this material withholds because of lime in the binder, as it may corrode metallic materials, reason for which it is recommended to protect your metals with high grade anti-corrosive enamels if use intended.

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Mabelle Plasencia

Founder and Editor at INmatteria©
• Architect | LEED AP BD+C, with an intense passion for materiality, innovation, technology and science. • Arquitecta | LEED AP BD+C apasionada por la materialidad, innovación, tecnología y ciencia.