Essential Prefab Straw Bale Construction: The Complete Step-by-Step Guide (Sustainable Building Essentials Series, 2) - Softcover

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Chris Magwood has designed and built some of the most innovative buildings in North America, including the first off-grid, straw bale home in Ontario which became a fifteen-year research project into the implementation of sustainable building materials and technologies. Chris Magwood lives in Peterborough, Ontario.

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The essential guide to prefab straw bale panels – an innovative development in one of the most widely used natural building methods

PREFABRICATED STRAW BALE wall panels combine the performance and low environmental impact of traditional straw bale with reduced labor and more consistent results. These "natural" structural insulated panels (SIPs) are built offsite and transported to the job site, or built onsite and "tipped up" into position.

Essential Prefab Straw Bale Construction is a fully illustrated practical guide to this affordable, scalable method. Going well beyond the scope of many natural building books, this indispensable manual includes a complete introduction to the use of prefabricated bale walls, packed with all the information you need to determine whether they are the right choice for your project. It covers:

• Specifications, engineering details, and building code references
• Comprehensive step-by-step instructions and detail drawings
• Finishing and maintenance techniques
• Budgeting and labor estimates
• Additional resources.

Containing over 100 illustrations and photographs, Essential Prefab Straw Bale Construction presents best practices from experience, research, and sound building science and engineering and the practical step-by-step information needed for high-quality prefab straw bale construction.

Chris Magwood has designed and built some of the most innovative, sustainable buildings in North America, including the first off-grid, straw bale home in Ontario. He is co-founder and director of the Endeavour Centre for Innovative Building and Living, and is the author of numerous books on sustainable building including Making Better Buildings and Essential Hempcrete Construction .

"The next generation of straw bale buildings is coming, and now we have a guide for builders, designers, and would-be manufacturers - from one of the best sources anywhere. As always, Magwood brings enthusiasm, experience, and solid science to the subject, so buy this book! Now! And prepare to learn, smile, and be part of a cool new generation of building!"
- Bruce King, Ecological Building Network, author, Design of Straw Bale Building

"Straw bale building has just grown up! Magwood has just shown us how to build sustainably for the masses."
- David Lanfear, Bale on Bale Construction

"Essential Prefab Straw Bale Construction is a jumping-off point both for professionals pondering unique, turn-key business opportunities and for novice ownerbuilders seeking an easier DIY approach to straw bale building. Accelerate your own research and development by several years in an easy weekend read."
- Ben Polley, Evolve Builders Group

"This essential guide covers it all, from the why and how to the nitty gritty details. Having explored a variety of modular and prefab delivery methods, with the help of this book, we foresee prefab straw bale becoming a favorite go-to solution."
- Anni Tilt, AIA & David Arkin, AIA, LEED AP / Arkin Tilt Architects

Sustainable Building Essentials

New Society's Sustainable Building Essentials Series aims to provide the highest quality information on sustainable building methods and materials. Editors Chris Magwood and Jen Feigin have scoured the world of sustainable building to bring you the techniques and systems that deliver measureable benefits in terms of greater energy efficiency and reduced environmental impact. Written by the world's leading sustainable builders, designers, and engineers, these succinct, user-friendly handbooks are indispensable tools for any project.

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Chapter 2 Rationale

Why Straw Bales?

While it may not initially strike one as possessing ideal qualities for construction, there are many compelling reasons for using straw bales as a building material.

Great thermal performance

Though some enthusiasts seem to imbue straw with almost-magical insulating qualities, the truth is that typical straw bales do not have remarkable thermal properties. Most testing has shown R-values ranging from 1.5–2.3 per inch,1 lower than many commercially produced insulation products. However, straw bale walls are widely attributed a whole-wall R-value of 30, which exceeds all current requirements in the International Residential Code (US) and the National Building Code (Canada). A more thorough examination of R-values is presented in the Material Specifications chapter.

However, these numbers don't tell the whole story because bale walls have real-world performance even better than their nominal R-value would indicate. There are several reasons for this, including a near-perfect distribution of thermal mass on the interior and exterior face of the wall, minimal thermal bridges in the wall, and a naturally airtight barrier on both sides of the wall. (See Building Science Notes chapter.) These factors combine to give excellent performance in a wide range of climates.

Good, cheap fill

Straw happens to be relatively inexpensive compared to manufactured insulation products and it comes in relatively large ready-made bundles. The wide straw bale wall (anywhere from 14–26 inches wide for standard bale sizes) insulates very well for a low cost. A square foot (0.09 m2) of bale wall at an approximate R-value of 30 would cost between $0.75–1.45. Bulk purchasing directly from farms can provide lower costs.

Decent structural qualities

Unlike the batt insulation materials in the cost chart shown here, straw bales have a density that allows them to play a structural role in the building. The straw bales in a wall are not the primary structural element of the wall; that role is handled by the vastly stiffer plaster skins2 for some types of S-SIP. Structural sheathing and/ or structural frames can give other types of panel the required structural rigidity.

Bales can be stacked without the need for any framing and still keep their form, and they can act as an excellent substrate for plaster, eliminating a number of components compared to conventional insulation types. They can even hold up a roof temporarily, and (with the right design) absorb earthquake forces for a surprisingly long time - giving a bale wall a resilience that can't be found in other insulation materials.

A by-product produced in vast quantities

Grain farming produces tens of millions of tons of straw annually. Each year, enough straw is produced in North America to build hundreds of thousands of homes. In the U.S., 54–56 million acres of wheat are planted annually,3 which could produce 6–7 billion construction-grade straw bales, or about 15 million homes each year. And this is only a single grain crop; there are many other viable crops for making straw bales.

Good carbon sequestration

Approximately 40–50% of the mass of a straw bale is carbon.4 At the code minimum of 6.5 pounds per cubic foot (100kg/m3), every 14"×18"×32" (355×457×800 mm) straw bale contains about 12–15 pounds (5.44–6.8 kg) of carbon. So, a typical 4×8-foot straw panel at the minimum bale density contains about 82–102 pounds (37–46 kg) of carbon. This is carbon that has been taken out of the atmosphere in a single growing season, and it will be contained in the wall of the building for a significant period of time. Wooden elements used in the construction of the panel also sequester carbon at a similar ratio of mass to weight.

As the harvesting and manufacturing of straw bales has a carbon footprint that is tiny compared to other insulation materials, this volume of carbon tied up in a straw bale panel can add up to a significant reduction of atmospheric carbon. A single 2,000 square foot (186 m2) home would typically use 40 straw bale panels, which means it would sequester approximately 3280–4080 pounds (1488–1850 kg) of carbon!

In Canada, about 200,000 new homes are built each year. If they were all built with straw bale panels, an astonishing 328,000–408,000 tons (298–370 million kg) of carbon could be sequestered annually. That would be a sizable contribution to meeting greenhouse gas reduction targets.

Nontoxic building material

Unlike most other building insulation materials, straw is very benign. Harvesting and baling do not involve any industrial processes or chemicals, and nothing is added to the straw in the bale. The straw does not off gas any toxins and remains a stable, inert natural material in the walls of the building. However, bales can contain dust and particulate, especially if stored in a barn, and appropriate breathing protection should be used during installation.

Why in Panelized Form?

Most of the benefits outlined above are as true of site-built straw bale walls as they are of prefabricated straw bale panels. So why panelize this wall system?

Labor reduction
Relatively high labor input has always been an issue with site-built straw bale walls. The stacking of the bales is not particular labor intensive, but the plastering requires many hours, a lot of scaffolding, and much skill to apply three coats of plaster to all wall surfaces. Wet-process panels, on the other hand, can be plastered with the wall in a horizontal position, using the panel framing to create a "container" for the plaster and a screeding surface to level the plaster. Plus, the plaster can be applied in a single coat because there are no issues with slumping and cracking as would happen with a single thick coat applied on a vertical surface. Plastering labor can be reduced by as much as 75% for panels as compared to site-built walls.

Site management
Straw bales are a bulky material, and coordinating their delivery to job sites - especially urban sites - is difficult. On-site storage of bales is highly inconvenient and messy, as large amounts of loose straw accumulate and spread around the job site. On-site plastering is also a very messy process, with large amounts of dropped plaster requiring thorough masking of all surfaces in and around the building and a lot of cleanup labor. By arriving on site with the wall system already finished, these hurdles are overcome, which could even promote the adoption of straw bale walls in more densely populated areas.

Predictability
Poor weather conditions don't slow down or halt a project, because the walls can be built indoors. Rain and cold temperatures don't affect the quality of the walls, and no on-site time is spent tarping or heating a project to try to keep a project moving.

Shortened build cycle
Panelized walls are installed very quickly - much faster than the on-site construction of any wall system. This greatly reduces the length of the on-site build cycle, helping projects to be completed faster and lowering costs for the builder.

No retraining or reskilling of on-site builders
A panelized straw bale wall does not require any special knowledge of straw bale construction or plastering for installation, allowing crews trained in general residential or commercial construction to take responsibility for the installation process, and presenting them with walls that accept doors, windows and roof framing in conventional ways....