FAQ
Q. How long does it take to build a natural home?
A. The time needed to build a natural house is highly subjective and ranges anywhere from 4 to 24 months. If you have a custom made house, the contractor tends to take longer. It can often take between 1 and 1.5 years to get ready for the construction process. If financing is not already in place and labor alternatives are an option, this will inevitably make for a longer process.
Q. WHAT IS COB?
A. Cob is one of the simplest and most ancient building systems in the world. It has been used extensively throughout much of Europe, Africa, Asia, and pre-Columbian North America. The word “cob” comes from England, where the technique was common until the 20th Century. In the county of Devon alone, there are more than 10,000 cob homes still inhabited, some of them over 500 years old.
Starting with sticky clay soil, you add water, usually sand, and straw. There are many mixing techniques, ranging from bare feet on a tarp to mortar mixers and backhoes. Once you have a homogenous mixture, firm but plastic, you use it to sculpt the walls in place. There is no formwork required and usually no reinforcement other than the straw. This allows for very curvaceous sculptural forms.
Cob walls have excellent thermal mass but poor insulation, making them a natural complement to straw bales in passive solar designs. Because it is sticky and malleable, cob combines well with many other building materials; it has been called “the duct tape of natural building.”
Q. WHAT IS Strawbale Building? - Hay vs Straw
A. Straw-bale construction is a building method that uses bales of straw (commonly wheat, rice, rye and oats straw) as structural elements, building insulation, or both. This construction method is commonly used in natural building projects. Research has shown that straw-bale construction is a sustainable method for building, from the standpoint of both materials and energy needed for heating and cooling. Using straw, you are taking something out of the waste stream. It is also a carbon sequestering building materials.
Hay is for horses, Straw is for houses. Straw is from cereal grains, rice in particular is high in silica and has anti mold and rot resistant properties.
Q. Will the straw decompose? What about Pests?
A. Plowed into the ground, most straw takes six months to decompose. Rice straw, which has a high silica content, takes twice that time. Straw has been used as an insulating material for many centuries, and has been found in excellent condition in Egyptian tombs thousands of years old. If kept dry, straw will not degrade. It can be said, then, that the lifetime of straw in a building could be anywhere from three weeks to nine-thousand years, depending on how well the building is constructed and cared for.
Straw has no nutritional value (unlike hay, which has seeds) and is therefore of little interest to rodents. Also, rodents would have to eat through thick plaster to get to a dense wall that is not food. Straw bales are not carriers of insects, the density of the packs makes it very difficult to move inside.
Q. Isn't there a huge fire danger?
A. No! Test after test show that straw bale walls meet or exceed fire code safety standards. A conventional wall (wood frame/drywall) is designed to withstand temperatures of 760 degrees Celsius (1,400 F) for 30 minutes. The National Research Council of Canada did a test on a plastered bale wall and it withstood direct flames of 760 degrees Celsius for two hours before a crack appeared. This rating is equivalent to cement (which means it can be used commercially).
Additional fire tests have been done by The Appropriate Technology Group at Vienna Technical Institute, The Danish Fire Technical Institute, University of California, and others. Depending on the size of the bale and the use of plaster the ratings ranged from 90 minutes to over two hours. In fact individual plastered bales were tested to the standards of Australian bushfires (up to 29 kilowatts per square meter of heat) and zero ignited. This qualifies them as “non-combustible” under Australian Bushfire code AS 3959.
Fire requires fuel, oxygen and high temperatures. Straw bales are highly condensed, decreasing the availability of oxygen and are coated as well.
Q. Aren't bales susceptible to humidity and moisture?
A. A coated straw bale wall is hygrophilic, which means it is vapour permeable and allows the moisture to wick in and then wick right back out again. People say the walls “breathe” because they allow moisture to leave. Permeable plasters like lime/earth are used to coat the bales.
Moisture getting into the bales is problematic during storage and the installation phase. If bales are not kept dry while being stored on the property, this can quickly become an issue. It is recommended that bales have no more than 20% moisture content. A moisture reader can tell you this. It is also advisable to tell your supplier this number and that you are using the bales to build with. You do not want to start your new construction with insulation that is holding moisture.
Q. Does straw bale meet building codes?
A. There is an International Straw Building Code which has been adopted by numerous states.
Q. How are the walls finished?
A. Walls can be finished in various ways. Plasters are a favorite choice for our clients and we tend to recommend lime exterior plasters and interior clay plaster finishes. Siding can still be used on the exterior. We work with our clients to design proper roof and foundation details to support whatever exterior finishes they are desiring.
The surfaces of straw bales offer an excellent mechanical bond to plaster and stucco, and reinforcement is generally not needed to attach plaster to the walls. Reinforcement may be desired when stucco is used as part of the structural system, or as assurance against hairline cracking. When needed, a variety of techniques can be used to attach netting, including long staples stuck into the bales or wire ties through the bale walls. Because of the natural undulations of a bale wall, an irregular pattern of attachment, rather than a simple grid, works best; care must be taken that the netting is uniformly secure. Also, wherever the bales abut a dissimilar material (e.g., at the mudsill, the ceiling and abutting stud walls), the wall should be reinforced with expanded metal lath that extends at least six inches onto the face of the bale.
Q.How do you incorporate plumbing and electrical?
A. Many builders use the precaution of installing pipes, which could sweat or leak, inside continuous sleeves within bale walls.
While ordinary non-metallic cable, such as Romex®* brand cable, is often used in bale walls, UF cable (rated for direct burial)
can be used where extra caution is desired. The Romex® brand cable, other nonmetallic cable, or UF cable is set three inches into the bale walls, safe from punctures. This also sets it into the firm portion of the bales, where it can be securely pinned. Electrical boxes are typically screwed to tapered stakes driven flush with back of recesses cut into the straw.
* Romex® is a registered trademark of Southwire Company.
Q. Do green/natural buldings last?
A. If designed, built and maintained adequately - these buildings can last up to 100 years. There are plenty of examples from around the world. Most strawbale homes that we are revisiting, have not needed any major maintenance. We typically get calls around the 20 year mark to repair plasters on the exterior that may be a bit too exposed to the elements. The structural integrity is still totally intact. Which is hard to say about other conventional homes, especially manufactured homes that tend to deteriorate between 10-15 years.
Resources gathered from the following:
*For more information on amazing sources of information, visit our Resources page.
CASBA
https://www.strawbuilding.org/faqs
Many Hands Builders
https://manyhandsbuilders.com/strawbale-building-blog/2017/1/29/strawbale-building-faq
The Fourth Pig
https://www.fourthpig.org/green-building-faqs
Straw Clay Wood
https://www.strawclaywood.com