Straw-bale construction
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.
[4][5][6] Disadvantages include susceptibility to rot, difficulty of obtaining insurance coverage, and high space requirements for the straw itself.
Straw bales were used in construction 400 years ago in Germany; and straw-thatched roofs have long been used in northern Europe and Asia.
When European Settlers came to North America, teepees were insulated in winter with loose straw between the inner lining and outer cover.
To combat this, builders began plastering their bale structures; if cement or lime stucco was unavailable, locally obtained "gumbo mud" was employed.
[2] This revival is likely attributed to greater environmental awareness and the material's natural, non-toxic qualities, low embodied energy, and relative affordability.
[15][16] However, in the USA, the introduction of Appendices S and R in the 2015 International Residential Code has helped to legitimize and improve understanding of straw-bale construction.
The bales may actually provide the structural support for the building[20] ("load-bearing" or "Nebraska-style" technique), as was the case in the original examples from the late 19th century.
[22] In this wall system the concrete skins provide structure, seismic reinforcing, and fireproofing, while the bales are used as leave-in formwork and insulation.
In South Africa, a five-star lodge made from 10,000 strawbales has housed world leaders Nelson Mandela and Tony Blair.
[25] In the Swiss Alps, in the little village of Nax Mont-Noble, construction works have begun in October 2011 for the first hotel in Europe built entirely with straw bales.
[26] The Harrison Vault,[27] in Joshua Tree, California, is engineered to withstand the high seismic loads in that area using only the assembly consisting of bales, lath and plaster.
[29] Straw bale domes along the Syrio-African rift at Kibbutz Lotan have an interior geodesic frame of steel pipes.
[33][34] given that the bales are over a foot thick, the R-value per inch is lower than most other commercial insulation types including batts (3–4) and foamboard (~5).
Bale walls are typically coated with a thick layer of plaster, which provides a well-distributed thermal mass, active on a short-term (diurnal) cycle.
The combination of insulation and mass provide an excellent platform for passive solar building design for winter and summer.
In common with most building materials, there is a degree of uncertainty in the thermal conductivity due to the influences of temperature, moisture content and density.
However, from evaluation of a range of literature and experimental data, a value of 0.064 W/m·K is regarded as a representative design value for straw bales at the densities typically used in building construction.
Measurements carried out in an innovative and sustainable house built in France have shown that this material helps to minimize heating degrees and energy consumption.
