Sustainable Architectural Services - Twisted Designs Ltd.

Straw Bale Information:

Twisted Designs Ltd takes a pro-active approach to Straw Bale Construction within the United Kingdom and we feel that Straw really is the future of the Construction -Industry for housing. The following web page is a basic introduction to building with straw in the UK and illustrates why Twisted Designs Ltd would like to have a greater involvement with straw construction and would like to see it implemented on a much larger scale.

What is Sustainable Development?

The idea is that sustainable development focuses on improving the quality of life for all inhabitants of the earth without increasing the use of natural resources beyond the capacity of the environment to supply them indefinitely. Sustainable development requires an understanding that not taking action has consequences and that innovative ways must be found to change our current behaviour. Sustainable development is not a new idea. Many cultures over the course of human history have recognised the need for harmony between the environment, society and economy. What is new however is an articulation of these ideas in the context of a global industrial and information society. Sustainable therefore means something that will last forever.

The concept of sustainable development was put forward by the International Union for Conservation of Nature and Natural Resources in 1980. (World Conservation Strategy 1980) However it wasn't until 1987 when the issues of sustainability and sustainable development came into prominence when the United Nations' World Commission on Environment and Development chaired by Gro Harlem Brundtland who later became the Norwegian Prime Minister, published its report 'Our Common Future.' (Our Common Future Document 1987)

The central recommendation of this document is that the way to square the circle of competing demands for environmental protection and economic development is through a new approach: sustainable development. The Brundtland report (1987) defined it as development that "meets the needs of the present without compromising the ability of future generations to meet their needs."

Straw as a Building Material

Straw is recognised as an experimental but environmentally friendly alternative to traditional construction. Unfortunately not many people, apart from environmentalists are aware of just how environmentally friendly straw is.

Straw can provide benefits where traditional construction cannot and surprisingly there is currently on average 4 million tonnes of waste straw produced in the United Kingdom each year. (Jones 2000 p15) Straw can be grown in less than a year in a completely sustainable production system and it can also be intercropped with other valuable crops such as wheat and barley, thereby increasing the yield and productivity of one piece of land. The sustainable yield of a piece of land is enhanced when each element in the sustainable system can provide multiple benefits and uses when the relationship of these elements is beneficial. This could be the case in places like the Steppes of Russia or the plains of China where timber is scarce and the climate is severe but straw is plentiful. In these instances straw could be turned into a renewable dominant building material and in addition to the other advantages of growing straw it can be grown on saline or low quality land, therefore making use of land that wouldn't have been considered previously.

This would mean a significant decline in the devastation of forests; it wouldn't cut out the use of timber completely because smaller amounts of timber are still needed in straw bale construction.

If the 4 million tonnes of surplus straw in the UK were to be baled and used for building, it would be possible to build 450.000 houses of 150m² per year. (Jones 2000 p15)

Straw rates highly as a sustainable material because it bypasses large amounts of energy that are needed to produce industrial building materials, therefore making it a clean and more environmentally friendly form of construction. Straw bale houses once constructed are more environmentally friendly than traditionally built houses. This can be for various reasons but the main reason is that straw is a material with high insulation properties and can provide long-term environmental benefits. Because of these insulation properties straw minimises the need to fit central heating, or fires, therefore reducing the energy use and heat emissions that create the carbon dioxide emissions and decreases the need for the burning of fossil fuels.

Most of the materials that can be used in straw bale construction are completely interchangeable with traditional construction methods. For example the use of concrete beam and block floors is quite common as is as opting to use Styrofoam insulation in the roof space. It can be quite easily used in both straw and traditional construction methods, but it would be entirely up to the owner/occupier of a straw bale house as to how environmental they want to be with their building materials and construction methods.

Construction Methods

There are two main forms of building styles with straw bale construction, they are the Nebraskan method and Post and Beam. The Nebraskan form of construction is a load bearing system, where the straw bales bear the weight of the roof directly without any additional support, and the weight is carried to the foundations by a combination of the bale walls and the plaster skins. (Steen, Steen, Bainbridge 1994 pp70-71.)

In the Post and Beam method, a wood framework carries the weight of the roof. However the frame could also be constructed from steel or concrete if necessary. The straw bales simply act as infill insulation blocks between the posts. The post and beam method has greater design flexibility allowing multiple stories, greater roof spans, higher design loads and larger window openings over the load bearing method. (Steen, Steen, Bainbridge 1994 pp100-103.)

Building Regulations

The Building Regulations Handbook states that there is no obligation to adopt any particular solution contained in an approved document if you prefer to meet the relevant requirement in some other way. The building regulations are a document that sets out the guidelines for building, and all new building are built in accordance with the Building Regulations. But as the above statement clearly indicates, it is possible to adhere to the Building Regulations and not use methods described within its pages. If there is an alternative way, then as long as it meets approval from the building inspectorate then it is possible to implement the chosen methods.

The Building Regulations aim is to ensure that whatever is built does not pose a health and safety threat in any way. The areas that Building Control will be most concerned with in straw bale construction are: insulation, fire, structure and durability of the building.

The amount of insulation in a material is measured by its U-Value. The U-Value is the amount of heat transmitted per unit area of the material per unit temperature difference between the inside and outside environments. (Sturges 2004.) The lower the U-Value the greater the insulation of the material. The building regulations currently require that external walls of a domestic dwelling must have a U-Value of 0.35 W/m^2oC or less. Because of the width and density of straw bales they have a U-Value of 0.13 W/m^2oC.

Research in the USA has concluded that straw bales are very fire resistant; this is because the straw bales hold enough air to provide good insulation value but because they are compacted tightly they aren't able to hold enough air to permit combustion.(Fernandez 1993.)

During the 1980's the National Research Council of Canada carried out fire tests of plastered straw bales and found them to be more resistant to fire than most conventional building materials. The research carried out by the Canadians found that plaster encased bales passed the small-scale fire test with a minimum temperature rise of only 110^oF over four hours. The plaster coating withstood temperatures up to

1850 ^oF for two hours before a crack developed in the plaster. Tests carried out in Mexico in 1993 proved equally positive. Proving that straw bales are very hard to ignite.

Further proof of straw's resistance to fire comes from a report of a house fire in San Louis Obsibo in California. During the summer of 1994 a forest fire with 300ft high flames engulfed the home of a local resident. The house was timber frame construction. There was nothing left of the house or its contents once the fire had dispersed. The one exception was a recently constructed plastered straw bale patio seat that absorbed a large amount of heat but did not burn. (Steen, Steen, Bainbridge pp42-43) This research clearly demonstrates straw as a potential building material in fire prone areas.

Research in the USA has shown that structural load bearing straw bale walls can withstand loads of more than 10.000lbs/sqft (Lacinski and Bergeron 2000. p120) Making it an adequate and sturdy form of construction able to withstand heavy loads. However it is the architects design of the associated timber structure that makes sure the loads are evenly spread around the walls. As can be seen from these requisites for Building Control, straw bale construction meets them all and in some cases surpasses the requirement.

The Financial Aspect of Straw Bale Construction

On average within the United Kingdom a straw bale costs 40p straight from the farm. A typical two storey three bed roomed house can be built with 520 straw bales with a total cost of £780 compared with a material cost of £5.000 for a brick and block wall traditionally built house of the same size. (Jones 2000 pp28.)

Just by changing the external wall material, can save the developer £4.220 this doesn't include labour costs. Brick and block walls using a team of 2 skilled labourers take's on average six weeks to complete. Straw bale wall tusing a team of 10 unskilled workers plus a trainer will take about 2 weeks to complete. (www.strawbalefutures.org.uk/)

Although the walls of a building this size only represent 16% of the total costs, £4.220 is a significant saving for a self builder and can become even more so for construction firms building more than one house. (Jones 2000 pp29.) Once any labourers that have had sufficient straw bale training the labour times for building with straw bales becomes vastly reduced.

However the most significant cost saving for straw bale houses is the long term fuel reductions it has due to the insulation qualities of the bales. Because of the high insulation factor, heating costs can be reduced by up to 75% annually compared with traditionally built houses, therefore the savings continue to accrue throughout the life of the building. (Jones 2000 pp16.) Unfortunately with most new straw bale houses being built in the United States and rarely in the United Kingdom the cost comparison associated with the building of the two methods has to be based on American building practices.

Twisted Designs, Ltd - Straw Bale Construction, Architecture, and Design.