Essential Prefab Straw Bale Construction: The Complete Step-by-Step Guide
96
Essential Prefab Straw Bale Construction: The Complete Step-by-Step Guide
96eBook
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Overview
The essential guide to prefab straw bale panels - an innovative spin on a widely used natural building method
Prefabricated straw bale wall panels combine the performance and low environmental impact of traditional straw bale with reduced labor and more consistent results. These structural insulated panels (SIPs) are built offsite and transported to the job site, or built onsite and "tipped up" into position. Essential Prefabricated Straw Bale Construction is a fully illustrated practical guide to this affordable, scalable method.
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
Essential Prefabricated Straw Bale Construction is part of New Society's Sustainable Building Series. Written by the world's leading sustainable builders, designers and engineers, these succinct, user-friendly handbooks are indispensable tools for any project where accurate and reliable information are key to success. Get the Essentials!
Chris Magwood is a sustainable builder and designer specializing in green and natural building techniques, the co-founder and co-director of the Endeavour Centre, and the author of several books on sustainable building including Making Better Buildings , More Straw Bale Building and Straw Bale Details .
Product Details
| ISBN-13: | 9781550926149 |
|---|---|
| Publisher: | New Society Publishers |
| Publication date: | 06/01/2016 |
| Series: | Sustainable Building Essentials Series , #2 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 96 |
| File size: | 28 MB |
| Note: | This product may take a few minutes to download. |
| Age Range: | 16 Years |
About the Author
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. He is a director of the Endeavour Centre in Peterborough, Ontario where he teaches hands-on workshops and is a lead instructor for the Sustainable New Construction certificate program. Chris is co-editor of the Sustainable Building Series and author of several previous books on sustainable building, including Making Better Buildings , More Straw Bale Building and Straw Bale Details . He is a regular contributor to Mother Earth News , Home Power and The Last Straw Journal .
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.
Read an Excerpt
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.
Who Would Want to Build with Panels?
There are many potential markets for prefabricated straw bale wall panels. Regardless of the market being addressed, one of the most attractive elements of this approach is the low cost of getting started. The initial investment in tools and machinery is very low, and only a flat and (preferably) covered space is needed. Getting started in the business of building S-SIPs has an impressively low entry threshold.
Stand-alone manufacturers
Several companies around the world have formed as straw bale wall panel manufacturers, specializing only in the building and installation of this type of wall system. With energy efficiency, carbon footprint, environmental impact and the high cost of labor being key issues in the construction industry, opportunities exist for companies with a product that can address all of these issues in a cost-effective manner.
Construction companies
Builders in the residential and commercial markets can benefit from building their own prefabricated wall panels. Crew members can build walls during slow seasons or during downtime, keeping workers productive. A stock of ready-to-install walls can allow more jobs to be completed, especially in climates with a limited building season or unpredictable precipitation patterns.
Owner-builders
A panelized system can allow an owner-builder to create a straw bale wall system without the need for a large crew. Wall panels can be built one at a time on the building foundation and tipped up into place at any pace or on any schedule.
Farmers
Wall panels can be built on the farm where the straw is grown, giving farmers a value-added option for their straw bales. Panels can be built during slow seasons or bad weather to maintain productivity and income diversity.
First Nations
Many First Nations are experiencing housing shortages. Panelized straw bale walls can be built in the community they are intended to serve, reducing construction costs and providing employment. Wall manufacturing could continue to be a source of revenue once immediate demand has been satisfied.
Opportunities for Innovation
It is early days for prefabricated straw bale wall panels. Most markets are wide-open to be served, and the technology and processes for building the panels are in their infancy. Current panel builders are using a lot of tools and materials borrowed from other types of construction, and none are employing a high degree of automation. All are working with field-produced bales, but the development of an on-site bale press that converts low-cost bulk straw (from jumbo round or square bales) into precisely sized, consistent bales would provide the significant advantages of consistency and further labor reduction. This is an exciting field for those with a passion for creativity and refinement of processes.
Notes:
- Design of Straw Bale Buildings. Bruce King, Green Building Press, 2006.
- Ibid.
- United States Dept. of Agriculture, Economic Research Service, Wheat Data Yearbook 2016.
- "Carbon sequestration in European soils through straw incorporation: Limitations and alternatives." D.S. Powlson et al.
- "Establishing a Methodology for Carbon Sequestration in Cotton Production in the US," Lanier Nalley et al.
Chapter 3 Material Properties and Appropriate Use
General Use Parameters
Prefabricated straw bale walls can be used as exterior and/or interior walls in most low-rise (three story or less) construction scenarios described in the International Residential Code (US) or in Part 9 of the National Building Code (Canada).
The 2015 International Residential Code includes Appendix S - Strawbale Construction, which outlines prescriptions and performance for site-built straw bale walls that can be applied to prefabricated straw bale panels in most cases. The inclusion of this Appendix in the U.S.-based codes could be of great help to anyone producing prefab bale panels by simplifying the process of obtaining building permits.
Suitability for larger projects and/or projects covered by other codes must be determined by the appropriate design professionals. To date, the panels have been used successfully as curtain walls in larger projects, up to six stories in height.
The panels can generally be considered to have structural characteristics that are equivalent to those of conventional wood frame wall systems and can be used in scenarios where wood frame walls are considered by local codes to provide sufficient structural integrity. Structural analysis for particular applications must be considered (see Testing Data in Resources). Panels can be used as structural load-bearing walls or in conjunction with a structural frame as infill walls.
Load-bearing walls
Prefabricated straw bale walls can typically be used as load-bearing exterior and/or interior walls in any scenario in which conventional frame walls are used. In these scenarios, the walls carry all the dead and live loads and transfer these loads to the foundation.
Infill walls
Prefabricated straw bale walls can be used as non-load bearing exterior and/or interior walls in any scenario in which a structural frame carries building loads and in which curtain walls are required. Infill walls can include those in which the frame of the prefabricated panel is designed to carry all structural loads without relying on the straw bale/plaster element.
Specific exclusions
Prefabricated straw bale wall panels should never be used as exterior walls in any below-grade applications, whether used as load bearing or infill. Use in flood plain areas should be restricted to elevations above anticipated 100-year flood levels.
Table of Contents
Acknowledgments
Chapter 1: Introduction
Chapter 2: Rationale
Chapter 3: Material Properties and Appropriate Use
Chapter 4: Building Science Notes
Chapter 5: Material Specifications
Chapter 6: Design Options for S-SIPs
Chapter 7: Design Notes
Chapter 8: Construction Procedure
Chapter 9: Installation
Chapter 10: Tilt-up Construction
Chapter 11: Finishing Installed Walls
Chapter 12: Maintenance and Renovations
Chapter 13: Building Codes and Permits
Chapter 14: Tools
Chapter 15: Conclusion
Glossary
Resources
Appendix: Engineering with Straw Bale Panels in Canada
Index
About the Author
What People are Saying About This
"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, Chris 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
"Essential Prefab Straw Bale Construction is a jumping off point both for professionals pondering unique, turn-key business opportunities and for novice homeowner-builders 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
"Not satisfied with the impact he's already made, Chris Magwood has given us a blueprint for building regenerative housing for the masses. No more baby steps - this book is a giant leap forward for straw bale building."
— David Lanfear, Bale on Bale Construction
"[Magwood is] way ahead of the curve as usual with this publication. And yet it is not a minute too early for the public to be introduced to this important advancement in the world of low carbon construction. Enclosed you will find everything you want to know about prefabricated straw bale construction and a bunch of other things you should know as well."
— Ben Graham, New Frameworks Natural Building
"Chris Magwood has been on the forefront of natural building and he once again shows his ability to bring things to the next level. Prefab straw bale may indeed be the catalyst that this incredible technology needs and Chris lays out the plan in detail in this book. From why it's important to how to get started, Chris inspires us to think bigger than ourselves. He takes us deeper into the actual "how-to" details in a way that allows the reader to step forward with confidence and bring the dream of prefab straw bale into reality."
— Andrew Morrison, www.StrawBale.com
"While it is not possible to create a standardized, code-approved individual straw bale, the use of prefabricated straw bale panels manufactured in a quality-controlled environment offers a system that will have predictable design parameters. As a researcher, educator and practicing engineer I believe that Magwood has provided us with a practical reference that can provide guidance for students and design professionals who know that the future of sustainable building will be found in creative alternative building strategies."
— Kris J. Dick, Ph.D, P.Eng., Associate Professor and Director, The Alternative Village, Department of Biosystems Engineering, Universityof Manitoba
"A book that should be in the hands of every builder, designer, architect, code official and home owner who wants to see better buildings built. Incredibly accessible and technically thorough, it is not often that a technical guide is also such an inspirational read. Every builder, designer, architect, building official and environmentalist will benefit from reading and re-reading this book."
— Melinda Zytaruk, Fourth Pig Green and Natural Construction
"Essential Prefab Straw Bale Building just blew the doors wide open for straw bale builders. Building on his success with his book Making Better Buildings, Chris Magwood has again written a game-changing book for us natural building geeks. Straw bale construction has been criticized as a niche-y, one-off kind of housing typology. Panels are an incredible solution to scalability and replicability of building with straw. My gratitude goes to Chris again for doing the research and testing for us."
— Emily Niehaus, founder/director, Community Rebuilds