Straw-Bale Construction

History

I n the late 1800’s, settlers in the Nebraska Sandhills region of the USA (an area with no trees and soil too sandy for sod walls) were forced to get creative in sourcing building materials for their homes.  The arrival of the modern, mechanical baling machine made many things possible, including the invention of the straw-bale wall system.  Covering the outside and inside of the bales with plaster (stucco) protected the bales and improved their air-tightness.  Residents soon realized the high level of comfort the walls provided.  Word spread, and many straw-bale buildings were built throughout the region and the world, including the Pilgrim Holiness Church in Arthur, NE (built 1928, pictured) and the ‘Maison Feuillette’ in France (built 1921), both of which are still standing today.

By the 1940’s, the mass-production of cement and oil-based building materials provided an affordable, attractive housing “package” that’s still common today.  Many of these homes strived to recreate the durability of natural materials like stone, but used unchecked quantities of energy-intensive, toxic ingredients.  Environmental awareness in the 1970’s and 80’s led to a modern resurgence of straw-bale construction in the USA and worldwide.  Today, there are straw-bale homes in all 50 states in the USA, and over 100 in Colorado alone.  The introduction of Appendices S and R in the 2015 International Residential Code has further supported and encouraged the growth of straw-bale construction.

How it Works

I n the early days, the stacked and plastered bale walls supported the load of the roof on their own (without wood posts).  This type of wall construction, known as “load-bearing”, is still used to a limited extent on smaller 1-story homes.  However, to achieve greater structural capacity and architectural freedom, the majority of straw-bale walls built today incorporate structural wood columns and bond beams (in various formats) to take vertical loads off the bales.  These walls are sometimes called “non-load-bearing”, although the bales and plaster are still used to resist lateral loads from wind and earthquakes.

A traditional straw-bale wall assembly consists of only three things:  exterior plaster, bales, and interior plaster.  There are no plastic vapor barriers, house wraps, etc.   The walls are naturally vapor permeable and extremely low in embodied energy.  They can also help create a healthy, non-toxic indoor environment.

FAQ:

How much does it cost compared to other wall systems?
The bulk material cost of bales is very low and comparable in price (per cubic ft.) to blown cellulose or fiberglass.  The material cost of clay plaster can be extremely low (cheap as dirt, basically), while prices for lime and cement-lime plasters will be roughly equivalent to other similar stucco finish materials.  As for “installed cost”, i.e. the price of the whole wall, fully built, this will of course depend on what contractor(s) you use and how much you do yourself, among other things.

Won’t mice and bugs get into the walls?
Pests will try to live in any type of house, no matter what the wall system is.  Good detailing that’s appropriate for your climate zone and geographical area will always help eliminate pest issues.  In a straw-bale home, the straw is sealed on all sides by either plaster or wood substrates, making it difficult for a pest to access.  And remember, straw is not typically a source of food for animals… Hay is for horses, and straw is for houses, we like to say.

How do you keep the bales from rotting?
Straw is made of cellulose, just like wood.  When exposed to moisture, cellulosic materials will decompose.  To keep wood-framed houses dry, we protect them with a good roof and a good foundation that keep moisture away from the wood.  The same is done with a straw-bale house.  When kept dry, straw (and wood) can last hundreds if not thousands of years.  In 2012, members of COSBA were able to obtain a straw bale that was taken out of an historic 1920’s bale house in Nebraska (to make way for an addition).  The bale appears as though it could have been installed a year ago.  Straw-bale walls also have the quality of being vapor permeable, which allows them dry out to the interior and exterior more easily than a conventional wall system.

How do they do if there’s a fire?
Contrary to popular belief, straw bales will not burn up spectacularly when lit.  They are too dense. Full-scale fire tests on straw-bale wall assemblies have been performed in accordance with ASTM Method E119-05a: Fire Tests of Building Construction and Materials.  An earth-plastered wall successfully obtained a 1-hour fire rating, and a cement-plastered wall obtained a 2-hour rating.  More information about the tests can be found at www.ecobuildnetwork.org.

How do you handle electrical and plumbing?
Electrical cables can be run in between bale courses or in small chases below/above the wall, depending on your wall design.  Some contractors also chose to use conduit.  Electrical boxes can be nailed to small wood posts or stakes that are fastened to or embedded in the bales.  In almost every climate zone, it’s generally not a good idea to run plumbing in exterior walls (to avoid freezing issues), and should be avoided in straw-bale walls to.  Where it needs to be done, using extra casing and air sealing/insulation is not a bad idea.  In “busy” wall areas like at a breaker box or mechanical room, consider switching to a more conventional framed wall system to improve access to cables and mounting equipment, etc.  Also note that locating showers next to exterior/straw-bale walls should be avoided.

Will my building department allow it?
The short answer is yes, they should, especially since straw-bale and light straw-clay construction systems are both now fully codified in Appendices S and R of the 2015 International Residential Code.  There shouldn’t be any type of “special” permit process.  COSBA can assist in educating building officials who are not familiar with straw-bale construction, which is a big part of our organization’s mission.

I’d like a straw-bale home but I don’t like the “stucco” look.  What do I do?
Recent innovations in straw-bale wall assemblies include various pre-fabricated systems as well  as rain-screen and  “straw-cell” assemblies.  With these systems, it’s possible to have a variety of different exterior and even interior wall finishes.

COSBA

C OSBA began in 2000 to address the growing need for public understanding of straw-bale construction in Colorado and the surrounding region.  We have held education workshops and annual conferences throughout the state that include keynote speakers, panel discussions, and local straw-built home tours.  In 2012, COSBA hosted the extremely successful International Straw Building Conference in Estes Park, CO.  We continue to promote the awareness of straw and all other natural building materials.  COSBA has held 501(c)(3) status since 2003.

 Our Mission


COSBA is committed to expanding and sharing knowledge, experience, and techniques for strawbale and sustainable building.  COSBA promotes quality building practices and serves as a resource to building professionals and homeowners.

 Our Vision


COSBA envisions a future where natural, non-toxic, low embodied-energy building materials are widely respected, understood & even preferred by the entire construction industry, including designers, builders, insurance companies, governments, code officials & the general public.