Common Concerns with Straw Bale Construction
Fire Safety:
The straw bales / mortar structure wall has proven to be exceptionally resistant to fire. The straw holds enough air to provide good insulation value but because they are compacted firmly they don’t hold enough air to permit combustion. The results of tests have proven that a straw bale wall has a far greater fire resistant than most conventional building materials. Subsequent fire testing has clearly shown the exceptional fire resistance properties of plastered straw bales.
Humidity and Moisture:
It has been successfully demonstrated that bale buildings are capable of surviving in humid climates, but it is critical to protect bales from direct exposure to moisture. Damage from water is by far the greatest potential hazard to a bale structure, hence buildings should be detailed to provide the necessary protection, otherwise problems may be experienced ranging from problems with mould and mildew to complete disintegration of the bales. The most vulnerable parts of a straw bale wall are the top and bottom, so the roof structure should go on as quickly as possible after the walls have been stacked, and if there is any delay the walls should be covered.
Pests, Allergies and Odours
One of the common worries about bale buildings is the threat of pests such as rodents and insects, however experience in both old and new bale houses has shown that this is an unfounded concern. Straw bales provide fewer spaces and havens for pests than conventional wood framing. When plaster is applied and maintained, access for even small insects is significantly reduced. Clean, bright straw has very little mold or allergy potential, asthmatics have had problems with moldy straw which should be avoided, even the less clean straw seems to be acceptable once sealed in a wall. Painted stucco plaster repels moisture but allows vapour to pass through the walls allowing for healthy internal air.
Building Codes:
Straw bale building can encounter the same problems with building codes as many other ecologically sound, proven methods of construction. With rammed earth and adobe houses, for example, unless there has already been a straw bale building approved by local building officials, the process of obtaining a permit can be lengthy. This may, however, be shortened by education and planning, flexibility and good communication channels with the relevant officials. New Zealand has hundreds of completed straw buildings and it is evident that they are solid, durable, and safe. Testing both overseas and here in New Zealand has demonstrated that plastered bales can easily meet building code requirements, and this has made it easier to have building consent approved by local bodies.
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