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FAQs - Straw Bale Construction

What are the most common concerns of using Straw Bales?

Fire Safety

  • Contrary to what one might think, straw bale structures have proven to be exceptionally resistant to fire. As straw bales are firmly compacted, they do not hold enough oxygen to facilitate combustion. Straw bales exposed to fire will smoulder and char, but will not burn.
  • Extensive fire tests have been conducted on straw bale structures by the National Research Council of Canada and by the State of New Mexico, and codes approving the use thereof are now in place.
  • "The results of these tests have proven that a straw bale in-fill wall assembly is a far greater fire-resistant assembly than a wood frame wall assembly using the same finishes."      (BAINBRIDGE & STEEN, 1994)
  • Fire retardants such as Boron may be used in high-risk areas, and as a further deterrent for termites and pests.



Termites and Pests

  • Experience in both old and new homes has shown concerns relating to rodents and insects to be unfounded. Straw bales have fewer spaces for insects than conventional wooden structures, and a well-applied and maintained coat of plaster denies access to even the smallest pests.  Furthermore straw is a dead material of no nutritional value, and thus insects are not attracted to it. An added precaution would be to treat the bales with a boron solution, which acts as an insect repellent (in most cases unnecessary). In termite prone areas it is recommended that a solid foundation and termite shield – such as a galvanized metal flashing – be used.



Allergies and Odours

  • Clean, bright straw has very little mould or allergy potential.  Hay fever is aggravated by the presence of pollen, which is mainly found in hay and not in straw. Asthmatics could still have problems with mouldy straw, however once sealed in with plaster there is no problem.



Humidity and Moisture

  • Damage by water is by far the greatest potential hazard to a bale structure, and buildings should be detailed to provide the necessary protection. Problems arising from water damage range from complete disintegration of the bales to problems with mold and mildew. During construction the bales must be kept as dry as possible at all times. Wall building should preferably be done in the dry season and the roof structure should go on as quickly as possible. If there are delays, the bales should be protected with tarps. The most vulnerable parts of a straw bale wall are the tops and the bottom, which must be protected with an adequate moisture barrier. The bale walls should be raised above ground level on a masonry plinth. The sides of bale walls are less problematic and buildings left unplastered and subjected to rain and snow have shown virtually no signs of deterioration. The problem arises when moisture becomes trapped within the walls.  For this reason, it is important to allow the bales to yellow or season before plastering is begun. Likewise time should be allowed for the plastering to cure properly before any finish coatings are applied. The idea of a breathing wall, which allows for walls to dry out, will avoid this potential problem.





 

 

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