Strawbale - Technological Performance
Performance parameters and properties:
Structural Performance:
| Property |
Units |
Description of Property |
Pertinent Test Protocols
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Typical Range of Values |
Codes of regulatory constraints |
| Load capacity |
pounds |
Strawbale can handle compression loads well.
Tension Loads are carried by beams and wire mesh.
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Consolidated Engineering Laboratories build a vault that weighed 5980 lbs. and supported 6700 lbs.
The vault's elastic limit was equal to 50% of its weight
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walls can hold a lateral load weight of 126% |
3605.5 - wall must support 400 pounds per square foot |
Thermal Performance:
| Property |
Units |
Description of Property |
Pertinent Test Protocols
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Typical Range of Values |
Codes of regulatory constraints |
| Heat Loss |
R |
How well heat is trapped inside the structure |
ORNL has tested straw bale systems by:
using hot plates or thermal monitoring technology
monitoring bale systems in a hot box
testing bale systems under ambient conditions
Modeling properties from knowledge about the system
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R-30 to R-45
Depends on bale size
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Bales are usually inconsistent regarding properties such as:
Moisture
Density
Conductivity of the bale
Emissivity of the straw surfaces.
Differences in these properties leads to inconsistent R-values
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Permeability Performance:
| Property |
Units |
Description of Property |
Pertinent Test Protocols
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Typical Range of Values |
Codes of regulatory constraints |
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Bales are highly resistant to damage and rot.
Few organisms can decompose straw bales.
Bales with moisture over 70% can attract fungi
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ASHRAE has conducted studies using the program moist. |
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Midwest and Northwest straw bale buildings should vapor diffuser retarders on the inside.
In the Soutwest they are not needed
In places where air conditioning use is high, vapor diffuser retarders should not be used on inside walls.
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Durability Performance:
| Property |
Units |
Description of Property |
Pertinent Test Protocols
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Typical Range of Values |
Codes of regulatory constraints |
| How the system holds up over time |
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The bales can usually last over long periods of time
Durability depends on moisture content, as well as bale densiy.
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Strawbale systems have proven to be more durable than most other systems when properly constructed
If moisture and insect protection is well built, bale systems can stand for long periods of time.
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3604.1.5 - Moisture must be less than 14% when put in
3604.1.6 Density must be at least 7.0 pounds per cubic foot
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Fire Performance:
| Property |
Units |
Description of Property |
Pertinent Test Protocols
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Typical Range of Values |
Codes of regulatory constraints |
| Fire Resitance |
Hrs. |
Determines how long the structure
will resist the effects of fire damage.
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-Attempt to burn versions of
strawbale walls.
-Measure time it takes for a
stawbale wall to lose structural
integrity when in contact with
fire.
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-Must perform under maximum
heat intensity being 29 Kilowatts
per square meter
- 34 min. w/ unplastered walls
and up to 2 hours with plastered walls
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-Bales must be tightly packed
-Must be shored with twine or wire
-Must be coated or covered with
sheetrock, plaster or stucco
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Indoor Air Quality Performance:
| Property |
Units |
Description of Property |
Pertinent Test Protocols
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Typical Range of Values |
Codes of regulatory constraints |
| Breathability |
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Straw bales allow transfer of air through walls
Bales are non-toxic
Indoor mold can penetrate through the bales when moisture from the air moves through.
Bales may not show signs of indoor mold until 10-12 years after the system was built.
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Aprovecho Research Center completed a two story dorm to test the air quality and mold resistance of straw bale walls |
bales start to decompose at a relative humidity of 85% at 70 degrees |
Bales should not be used where relative humidity is above 70% for long periods of time. |
Sources
http://www.humboldt.edu/~ccat/alternativebuilding/strawbale/tonySP2002/strawbaleconstruction.html
http://www.skillful-means.com/strawbale/papers/vault_report.htm
http://www.dcat.net/resources/Austin_Straw_Bale_Code.pdf
Buyer's Guide:
| Stakeholder -group |
Homeowner
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| Structural |
- As strong as any other structure – dependant on structural design
- Walls can be load bearing or non-load bearing
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| Thermal |
- R 2.7 per inch
- 18 inch wall is R 48
- Potentially 75% savings in Heating and Cooling Costs
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Permeability
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- Needs to be able to breathe for moisture evaporation but otherwise very good
- Stucco/Plaster are commonly used coatings and very good material for the straw
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| Durability |
- As long as the straw is protected and installed correctly, there will be no problems
- Sealing the walls is important in preventing rot
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| Fire Performance |
- Very good ratings with a stucco or plaster coating on the outside
- Compacted straw takes a while to burn
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| Indoor Air-Quality |
- Bales allow a gradual transfer of air through the wall, bringing fresh air into your living environment, especially when combined with a natural plaster. (http://www.epsea.org/straw.html)
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Previous information attained from (http://www.epsea.org/straw.html)
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FMEA Analysis:
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Function
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Elements
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Modes
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Causes
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Effects
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Structural
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Metal Frame
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Massive Vibrations
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1) Natural Disasters
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Weakening of Supporting Members (rebar / dense straw)
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Weakening Rebar
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2) Water
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Wood/ Rebar Frame
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Rotting
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3) Rodents
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4) Extreme Heat
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Thermal Insulation
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Straw
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Penetration
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1) Water
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Straw will rot, losing the insulation value.
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2) Wind
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Waterproofing
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Waterproofing layer (stucco/plaster)
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Falling off
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1) Stucco not applied properly
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Will provide hole or crack in wall that will allow water to reach insulation
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Overhangs
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Cracking
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2) Movement of Straw-bales
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Vapor Barer in joints
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Dent
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3) Objects hitting wall
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Fire Performance
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Straw-bale
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Spark (Fire)
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1)Stucco broken to allow access to straw
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Dry loosely packed straw provides the perfect fuel for a fire
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Cement based Stucco/Plaster
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Combustion
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2)Straw bales not packed tight enough or packed to tight
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Waterproofing failures cause the straw within the wall to begin rot. Which continues to deteriorate until all the straw is gone. If all the straw is gone from within the wall then there is not insulation to keep the house warm or cold.
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Loosely bundled straw bales provide a good opportunity for a fire to be started if it is able to be caught by something.
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If water gets into the wall then the supports including rebar, wood, and metal frame it could cause the wood to rot and the rebar and metal to rust.
http://news.bbc.co.uk/2/hi/uk_news/england/southern_counties/5380666.stm (fire)
http://www.20-20homeinspections.com/id4.html (crack)
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Third Party Evaluation/Information Sources
The Development Center for Appropriate Technology
Link to Source
http://www.dcat.net/resources/index.php - Austin Straw Bale Code
Summary
This page has information on codes for building with straw bale in specific regions. It covers materials, construction requirements, and gives a minimum standard for construction with straw bale. Has information on testing your material before construction and basically outlines the limits and dimensions for building with straw bale. It also has test results on fire testing and moisture testing.
CARS Checklist
Credibility: I think this is a very credible source because the Development Center for Appropriate Technology is a non-profit organization. The site gives resources that have the writer's information and states the organization that carried out the tests. The site is organized well giving it evidence of quality control.
Accuracy: This source has a good amount of evidence that it is accurate. The information is from within the last 15 years so it is relevant and useful. The information is intended for builders wanting a standard for working with straw bale. It is mostly codes made about straw bale and then the codes that are developed after these tests so it pretty straightforward.
Reasonableness: This organization's purpose is to test systems and share the information so it is safe to believe that it is fair. There is no writer's view or inconsistency because it is codes.
Support: The pdf's on this page give direct sources to where the information comes from so it has excellent support. I could not find many other sources with this information so I couldn't develop the corroboration of DCAT with nothing to compare it to.
The Last Straw: The International Quarterly Journal of Straw Bale and Natural Building
Link to Source
http://www.thelaststraw.org/
Summary
This source is a comprehensive journal that shares news and developments about straw bale. Includes everything from codes and tests to vast articles of information on straw bale and resources for practically anything about this building system. The site also has a centralized directory of suppliers for straw bale.
CARS Checklist
Credibility: The articles give the author's information as well as the editor's including contact information. The site is very organizational and has strong signs of quality control.
Accuracy: They have an archive of all issues and articles so the information is being developed constantly. The site's purpose is to compile the latest technical information and share it so it is relatively comprehensive.
Reasonableness: The only precaution that I can find is that everyone has opinions and the authors could have slight bias in their articles. Considering the audience and the organizations it is safe to say it gives a fair view of the information. There are no wild claims and shows signs of moderation.
Support: All information is organized and sited properly. The site has it's own page on all of the information used by their authors. Most of the information is confirmed and can be found in other places.
Green Home Building
Link to Source
http://www.greenhomebuilding.com/strawbale.htm
Summary
Green Home Building is a resource and research website with comparative information and catalogues references for more information on straw bale. The author writes about the good and bad of straw bale like load bearing and non-load bearing and the differences between this system and others.
CARS Checklist
Credibility: The source gives extensive information on the writer and contact information. There is a small bio section for each author. The author's current title is Founder and Director of the Geiger Research Institute of Sustainable Building. This information makes it a very credible source.
Accuracy: A date could not be found for the specific straw bale article making the accuracy a little skeptical. The author is very comprehensive and acknowledges the pros and cons of the system.
Reasonableness: From the information stated in the article there appears to be no hidden agenda or bias form the author. All ideas and claims are rational. The article is consistent and gives a fair view on the matter.
Support: This is a source coming directly from an expert. There are no sources for this specific article because it is the knowledge from the author. This makes the credibility a little less because of it.
I would say all of the sources rate very high on the CARS checklist. The DCAT would have to be the "best of breed" of the resources because it faired the best on the CARS checklist. It is a non-profit organization with code and test information and no "author" that would have bias views.
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Relevent Trade Associations:
California Straw Bale Association - A non-profit organization whose members are architects, engineers, builders, and people interested in straw building. Goal: to further the practice of straw building by exchanging current information and practical experience. Click here for the link to the California Straw Bale Association website
Straw Bale Association of Texas - Dedicated to promoting straw bale construction in Texas. The group is based in Austin, but is a focal point for straw bale building activity across the state. Click here for the link to the Straw Bale Association of Texas website
Straw Bale Association of Nebraska - Organized in January 1998 as a network of straw bale builders and enthusiasts. SBAN provides information, coordination, assistance and resources to promote and develop straw bale construction. Click here for the link to the Straw Bale Association of Nebraska website
Colorado Strawbale Association - COSBA is committed to expanding and sharing knowledge, experience and techniques for straw bale and sustainable building. COSBA promotes quality building practices and serves as a resource to building professionals and homeowners. Click here for the Colorado Strawbale Association website
http://www.ecobusinesslinks.com/straw_bale_house.htm
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Lessons Learned Analysis:
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Phase-Out Analysis and Lessons Learned
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Project/Task:
Assignment 3 - Strawbale Technology Performance
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Date:
1 October 2008
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Team Name:
Team 5
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Members:
Zegowitz, Danner, Jones, Allen, Sammon
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Subtask
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What Worked
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What Didn't Work
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Ways to Improve
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Dividing up Tasks
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Members choose the best bullet that they thought they could accomplish; everyone was in agreement
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Every team member working on the same tasks or on all portions together.
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Each member completing their work on time
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Each member was efficient and prompt in having tasks completed in the timely manner.
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Checking to making sure everyone completed their work on time
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Lab times and meeting dates were desgined to give updates of the status of the completion of work.
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Create Powerpoint
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Having completed worked in time to have powerpoint slides readily available for presentations.
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Present
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Finish/Organize the Wiki Page
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Target Analysis: How well did the project/team do...
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In achieving goals and meeting project objectives?
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At meeting deadlines and the final completion date?
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At monitoring and staying within project budget?
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At communicating with stakeholders?
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Resources Assessment: were the allocated resources appropriate, sufficient, and efficiently used?
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Lessons Learned: what are the key lessons that can be applied to future projects?
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Phase-Out Analysis and Lessons Learned
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Project/Task:
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Date:
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Team Name:
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Members:
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Subtask
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What Worked
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What Didn't Work
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Ways to Improve
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Target Analysis: How well did the project/team do...
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In achieving goals and meeting project objectives?
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At meeting deadlines and the final completion date?
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At monitoring and staying within project budget?
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At communicating with stakeholders?
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Resources Assessment: were the allocated resources appropriate, sufficient, and efficiently used?
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Lessons Learned: what are the key lessons that can be applied to future projects?
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Facts
Advantages:
- A straw bale construction system has an average R-value in-between R-35 and R-48. Because of this, using straw saves up to 75% of energy costs.
- The walls have superior sound insulation
- They can withstand severe whether and wind conditions
Disadvantages:
- If oxygen or water leaks into the bales of straw, they are at rick of decomposing.
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