STRAW BALE

HISTORICAL BACKGROUND ON STRAW BALE

Straw the stalks remaining after the harvest of grains such as rice, barley, and wheat. Is one of the finest renewable resources which can be used as a building material grown annually each year, found around the world in abundance (Kings, 2003).
According to Matt’s (1994), a straw bale expert, “Each year 200 million tons of straw are underutilized or just wasted in most countries, so also, from the harvest of the united states major grains could be used to construct five million 2,000 square foot houses every year.
Just like trees, straws are chemically composed of primary cellulose. When composed together into a bale, it forms solid block that are resistant to decomposition, and when covered with plaster skin, it creation is beautiful, strong, stable, moisture resistant and above all, energy efficient (Adedeji, 2003).
People have built homes using straw grasses, even early settlers of the grasslands of Nebraska discovered the beauty of straw bale homes over 100 years ago, According to Roger (1994), “it was inevitable that some settlers, desperate for a cheap, available building material, would eventually see the big, solid, hay blocks as a possibility.
These settlers of Nebraska, Confronted with cold winter, a lack of trees and a need for a quickly built out building, straws became a solution. These bales were put on roofs and used as insulation against the cold was found and exceeded any wood building.
Straw bale structures have consistently withstood severe weather and earthquakes. The earthquake was in the 1970s and it was either 5.3 or 5.8”. Chuck Bruner, a resident of one of the houses told the mother earth news after the earthquake, “there wasn’t a single crack in the house”.
With every year, around the world the benefit of building with the straw bales cannot be over emphasized (Harvest Homes, 2003).

STRUCTURAL PROPERTIES

The primary requirement of straw bale buildings unlike any order form of building being constructed today is to withstand the dead, live, and imposed loads thereby transferring load to the foundation and then distributing them to the ground. (Walker, 2004).

MATERIAL PROPERTIES

When picking a material for building purposes, the properties of the material is first put into consideration, so also is the choice of the builder and the actual material he has in mind to accomplish the project. This is no different when choosing a straw bale as a building material.

MOISTURE EFFECT / RESISTANCE

Straw bale walls should be highly protected from moisture as moisture could cause damage and provide room for pest’s invasion. In some cases, rocks are used to decorate the bottom exterior of the home to prevent raise of moisture, so also well maintained guttering, purches and verandas and suitable render materials are applied to straw bale buildings to avoid direct rain exposure. The moisture content in a straw bale wall should not go beyond 15% (Mohamed, 2003).
The California straw bale code (2001) came up with the statement that the water content in a bale during installation must not exceed 20% of the whole weight of the bale.

AFFORDABILITY AND AVAILABILITY

Straws, as they are known to be waste after the harvest of grains like rice, wheat, and oats, are low cost materials found around us. Sometimes it can be gotten free as some farmers prefer to burn them, (Harvest Homes, 2003).

RESISTANCE TO PESTS

Plastered straw bale provides little or no room for pests, straw bale also provides fewer havens for pests like termites than conventional wood framing (Harvest Homes, 2003).

ACOUSTIC PROPERTIES

Noise has been defined as unwanted sound which can be detrimental to health, could cause damage to the ear or loss of concentration. These sound should be controlled especially in buildings like churches and cinema houses, sound transmits less in medium which are air tight, which is the reason for the high sound insulating property of straw bale buildings (Adedeji and Bello, 2011).

Several acoustic data’s were lined out by some anthologies.

According to Minke and Mahlke, (2005), depending on the frequency, a 45cm thick straw bale wall, plastered on both sides, provides a noise level difference of 43 to 55 dB.
So also, King(2006) who measured the sound transmission of a 20 inch thick stuccoed wall and came up with a noise level of 59.8 dB.

FIRE RESISTANCE

Combustion only takes place in presence of oxygen.Air is the power force behind any fire outbreak. Straw bale blocks are tightly packed and compressed together to form the block which provides no chance for pores or holes, thereby stopping any chance of air or oxygen coming into it. Since these straws are densely packed, without any space for air, the fire resistance of the material is superb (Downton, 2003).

According to the national research council of Canada (NRCC), plastered straw bale was tested for fire safety and was found to be of better fire resistance to most conventional building materials. After the test, it was found that the plastered straw bale withstood heat up to 1,850 F for two hours before it started showing cracks.

So also according to the Canada Mortgage and housing corporation, the straw bale / mortar structure wall has proven to be exceptionally resistant to fire. The firmly compactness of the straw, in addition to the plaster coating makes it impossible to accommodate air to support combustion (King, 2003).

REFERENCES

Abdullahi, M. (2006). Properties of some fine Aggregates in Minna, Nigeria and Environs, Leonard Journal of Sciences, 8, 1-6

Adedeji A.A (2007). Introduction and design of straw bale masonry, Olad publishers ENT.

Ilorin.

Anderson , Leaver, Alexander and Rawlings, Material Science, Nelson publishers.

Baiden, B.K and Tuuli, M. (2004). Impact of quality control practices in Sandcrete Blocks Production, Journal of Architectural Engineering, 10(2), 55-60

British Standard (BS) 12-Specification for Portland cement BS1, London

British Standard Institution (BS) 1968 – Precast concrete B. London: BS1

British Standard Institution: Specification for Aggregates from natural sources for concrete. BS 88.2 Park Street, London, 1983

California straw bale building code(2001). HS18944

Case and Chilver (1989). Strength of materials and structures, Edward Arnold publishers.

Cazaud, R., Fatigue of Materials (1953). Chapman Hall.

C.H. Ryder (1969). Strength of Materials, English language book society and Macmillan   publisher.

Downtown (2003), Australia straw bales. Australia.

Fenner,A,J ,Mechanical Testing of Materials(1965). Newnes.

Harvest Homes company (2003). Canada, www.harvesthomes.com

King, B. (2003). Load – bearing straw bale structures, U.S.A

Lee, F.(2001), Straw bale construction, U.S.A

Lacinski, P., and Bergeron. (2000) serious straw bale; a home construction guide for all     climates. Chelsea Green publishing co. U.S.A.

The Last Straw: Back issues No 53 & 56

Myhrmam, M, MacDonald, S, (1997) Build it with bales

The nine myths about straw bale-PacquaioYavis, Craysons publishers (2001).

Todd, Structural theory and analysis, Macmillian publishers (2003).