Strawbale construction methods and future viability in the United Kingdom

¶ … Strawbale Construction Methods in the United Kingdom

In an era that demands sustainable and ecologically sound construction methods, one approach that is gaining increasing attention and acceptance in recent years has been strawbale construction. Introduced more than a century ago when baling method began to produce bales that were sufficiently dense for load-bearing wall construction, strawbale structures have proven their durability, functionality and aesthetic appeal. The purpose of the study proposed herein is to delivery a comprehensive review of the relevant literature to identify the advantages and disadvantages of this construction method compared to traditional construction methods, and to develop a series of case studies concerning current strawbale structures in the United Kingdom in order to identify these respective attributes. The goal of the proposed study is to determine whether there is a future for strawbale construction methods in general and in the United Kingdom in particular, and if so, whether some types of structures are better suited for this construction method and why.

Problems and Specification

The traditional construction methods that are used most widely today have evolved based on thousands of years' of trial and error and have been designed to satisfy sophisticated building codes that are intended to protect the inhabitants from the rigors of Mother Nature. Moreover, contractors and engineers have invested their entire careers in learning how to use traditional building materials such as concrete, reinforced glass, steel and lumber to their best effect while satisfying the standards set forth in building codes and it is not surprising that there is little interest from these professionals in alternative building materials that might be suitable replacements for these traditional materials. Nevertheless, there is a groundswell of interest from others, including the so-called "green" movement and alternative lifestyle enthusiasts who have embraced strawbale construction as a superior approach for a wide range of structures, including residences, classrooms, theaters, and barns. Indeed, straw is a readily available, inexpensive and easy-to-use construction material and its advantages in construction include its thermal, acoustic, lack of toxicity and even its aesthetic qualities. While there are some disadvantages to its use, including its susceptibility to damage by moisture, these disadvantages can be overcome and are clearly outweighed by the wide range of benefits that accrue to its use. Therefore, the above-stated purpose and goal of this study are timely and relevant enterprises in an era that demands improved building materials that are ecologically responsible, inexpensive and readily available.

Literature Review

According to a study by Pritchard and Pitts (2006), the use of straw as a building material is certainly not new, and dates to prehistoric times; since time immemorial, straw has been used in roofs, walls as well as an insulation material. Although it has been used in these and other capacities as a building material for thousands of years, it has only been within the past century-and-a-half or so that it has been used for the type of construction method that is the focus of this study. It was during the Industrial Revolution that straw-baling machines were introduced that provided bales that were sufficiently dense that they could be used virtually exclusively in load-bearing walls (Pritchard & Pitts 2006). Indeed, Shiamh (2008) emphasizes that, "Straw bale building began shortly after the introduction of the baling machine in America. There are still straw bale houses standing today that have stood the test of time and the elements" (3). There are two primary ways to use strawbale in construction:

1. The Nebraskan or load-bearing design approach which involves using the strawbales like bricks and where the roof is directly attached to a plate that is affixed to the top of the baled walls; and,

2. The infill method which, as the term implies, using strawbales to fill in the spaces between walls constructed from traditional building materials such as wood, concrete or steel (Shaimh 2008).

As noted above, there are some disadvantages to using strawbales in either of these two construction methods, including their susceptibility to damage by moisture and their tendency to attract vermin; nevertheless, properly installed and covered, these disadvantages are usually minimal and are far outweighed by their numerous advantages. In this regard, Shaimh emphasizes that, "Straw bales are one of the most low impact materials one can use in building. They offer a U. value (insulation) of about 0.13, which is highly insulating. It is a growing art and industry and one to celebrate as a way forward for new builds and communities in this time; an alternative to the mass energy and waste created in building projects over the past fifty years since the concrete industry emerged" (Shiamh 2008, 3). Their excellent insulation qualities are also discussed by Pritchard and Pitts (2006) who note that, "It is clear that strawbale construction compares favourably with the principal competing low-U-value wall designs. Also, at the end of the building process, in contrast to much modern practice, the majority of the building waste can be recycled or used as mulch, reducing the load on municipal landfill and incineration facilities" (372).

Consequently, strawbale construction methods offer a means for professional builders as well as the do-it-yourselfer to create ecologically responsible and cost-effective buildings in ways that other materials do not. Strawbales also have a number of other advantages in construction projects of all types, including low toxicity of the material, outstanding thermal properties and insulation qualities, it is resistant to earthquakes, it is inexpensive, easy to use, and aesthetic appeal. For instance, Pritchard and Pitts emphasize that although an ugly building can be constructed from any medium (including strawbales), "Strawbale building appears to lend itself to a simple elegance of form which most find strongly appealing, and frequently to a sense of womb-like comfort and protection inside the building. The material permits a wide variety of shapes of building plan, accommodating curved as well as straight walls" (373).

Of particular importance to ecologically minded builders in the UK is the fact that straw is especially abundant. According to Pritchard and Pitts, Straw is generally readily available from local sources in many societies; for example, in Britain, about 22 million tonnes of cereal grains are produced annually, generating approximately 13 million tonnes of straw as a by-product" (Pritchard & Pitts 2006, 372). Moreover, in spite of the broad range of applications for which straw is used, there is inevitably a surplus amount of the material available in the UK and it is also relatively inexpensive (Pritchard & Pitts 2006). It is little wonder, then, that a growing number of builders have become interested in strawbale construction methods in the UK in recent years. For instance, according to the Strawbale Building Co. (2009), "Strawbale building is the use of straw bales to construct anything from a basic shed to a wonderful family home. It is part of a rapidly expanding natural/sustainable building movement here in the U.K. (2). A partial listing of existing strawbale structures in the UK include those shown in Table 1 below.

Table 1

Current Strawbale Structures in the UK

Name/Location

Description

Strawhouse B&B/Putley, Herefordshire. HR8 2RL

Two-storey hybrid load-bearing / non-loadbearing house; 2,500 square feet; 4 bedrooms, 3 baths; lime-plastered exterior

Centre for Alternative Technology (CAT)

Machynlleth, Powys, Wales. SY20 9AZ

Strawbale theatre and other buildings; also offers courses and workshops

Strawbale Classroom/Carymoor Environmental Centre, Dimmer Lane

Castle Cary, Somerset. BA7 7NR

Strawbale classroom, 30 square meters; load-bearing; also operates courses and workshops

Strawbale/Cordwood house and Permaculture holding.

Caroline Barry

Brook Farm, Barton Road, Butleigh

Glastonbury, Somerset BA6 8TL

Timber frame, two strawbale walls, two cordwood walls; lime-plastered exterior.

Hessian/limewashed interior; owner designed.

Strawdance Studio, Hertfordshire

Six-meter diameter cylindrical dance studio; features a clear roof. Outside unrendered. Set in woodland

Strawbale residential complex,

Powys, Wales

1. Strawbale multi-purpose conference / workshop/rehearsal space -- approximately 1,320 square feet; and,

2. Strawbale fully equipped communal kitchen/meeting place

Strawbale barn, Deanburn Cottage

Hayford, Buckfastleigh

Devon TQ11 0JQ

Post and beam/strawbale infill on limestone block foundation, approximately 30 square meters. Built in 1999 by Kevin and Helen Ireland. No cement or concrete used in building. Built with permission of Dartmoor National Park Authority; also serves as location for strawbale building seminars

Strawbale building,

Monkton Wyld Court

Charmouth, Bridport

Dorset DT6 6DQ

Load-bearing strawbale walls on a raised wooden deck on telegraph pole "stilts," approximately 400 square meters, lime-plastered exterior, mud plastered interior, tin roof, underfloor straw insulation, stained glass window, built in 1999 during a workshop

Strawbale house

Cork Racecourse, Mallow

Co. Cork, Ireland

Load-bearing strawbale walls, lime-plastered exterior, thatched roof, built during a workshop as part of the Mallow Homes and Gardens Festival where it was the star of the show and was admired by thousands

Source: Strawbale Construction Co. 2009

Finally, in what many observers would describe as a "three little pigs"-type structure, but which the owner describes as a "woodland eco home which is a self sustainable and low carbon build," the house pictured in Figure 1 below is the first two-storey load-bearing strawbale construction structure in the UK which clearly demonstrates the curvature possible with strawbale construction techniques (Shiamh 2008). According to its designer and builder, "It is created from low impact and natural materials. It has an off grid system powered by the sun and the wind. It uses bio mass heating with coppiced wood from the woodland, a rainwater harvesting system and all waste is composted on site through an aquatron system" (Shiamh 1).

Figure 1. "Eco-Friendly" Strawbale House in Penwhilwr in St. Dogmael's

Source: http://www.gwaliaessences.co.uk/img/strawbalehouse.jpg