Archive 2016 08

19 Modern Methods of Construction is the structure and insulation, while the infill method has a frame structure, usually timber, so straw is used only as insulation,” says Jones, who warns that buildings should not be built more than four storeys high without a frame. The hybrid is a mixture of the two, while the pre-fabricated version is factorymade straw and timber panels “that make the building flat and block-like but can speed up build time.” One of the key benefits of straw is that it creates little waste, adds Jones. And any waste produced can be used for horse bedding and garden mulching “therefore straw addresses climate change and cleans up construction.” Straw is easily accessible, energyefficient, has good acoustic properties and stores carbon instead of releasing it so you end up with a carbon negative building, explains Jones. Straw-built homes create a healthy internal environment, says Jones, and when combined with clay or lime plasters it regulates humidity, prevents condensation and mould growth. “People say it feels cosy, warm and peaceful inside,” she says. Despite it being “fun to work with”, Jones believes a lack of awareness within the construction industry and an unwillingness to try something different is limiting the use of straw as a building material. “Construction methods for loadbearing or infill techniques are very different to mainstream construction so it doesn’t fit easily with accepted ways of scheduling and working, although the pre-fabricated version does,” she says. Although skills can be taught quickly, Jones says anyone looking to work with straw must learn how to build effectively with it otherwise “you won’t have an airtight and thermally efficient building.” She suggests newcomers to the material take a look at what’s on offer at the School of Natural Building. Grow your own home with hempcrete When it comes to new, versatile and sustainable building materials, what is better than one you can grow yourself? Made from the shiv or inside of the hemp plant and then mixed with a lime base binder, hempcrete, like concrete, is strong, lightweight and breathable. It is best used to insulate masonry constructed buildings or as an enveloping insulation when used in conjunction with timber-framed buildings, explains Stephen Samuel RIBA, director of East Yorkshirebased chartered architects, Samuel Kendall Associates. Waddington homes built naturally with straw MADE almost exclusively from natural materials, two semi-detached houses in Waddington, Lincolnshire, were the first council houses to be designed by Jakub Wihan and Barbara Jones of Straw Works. Built by Amazonails in partnership with Taylor Pearson, the North Kesteven Council Housing properties are made of loadbearing straw and required no framework. The foundations are gravel trenches with a brick plinth wall laid with lime mortar, and foamglas blocks to the interior giving a U value of 0.17. Double glazed timber windows and FSC accredited timber was used throughout as well as sheepswool insulation to the roof and ground floor. The design has a loadbearing straw party wall, and the acoustic test showed that although all the accompanying details for the floor, wall plate and roof connections were excellent, the plastered strawbale wall on its own failed in the lower registers. This led to the addition of a 50mm stud wall in front of one side of the party wall, filled with sheepswool insulation and covered with plasterboard and skim enabled it to pass. The method used to protect the building from the weather during the construction phase – placing the first floor and wall plate on top of scaffolding, then doing the same with the roof – is not recommended as it is an expensive solution. More recent methods are to build the floor and roof first on temporary posts and beams and then lower them after the straw is installed. n Concrete Canvas CONCRETE Canvas (CC) is a revolutionary material technology that is changing the way contractors and consultants approach engineering projects, says Vladimir Mironov of Concrete Canvas Ltd. “It is a flexible concrete impregnated fabric, which hardens on hydration to form a thin, durable, water proof and fire resistant concrete layer. “Essentially it can be described as ‘concrete on a roll’ and has a wide range of applications such as ditch lining, slope protection, bund lining, weed suppression, concrete remediation and culvert repair.” n It can be used to insulate floors, ceilings and pitched roofs and once its special properties are fully understood it “can significantly simplify the construction and insulation of buildings,” says Samuel, whose family practice in Catwick, Beverley, prides itself on creating homes for real families. It can be used in the construction of new buildings and to refurbish existing buildings “where perhaps a change of use occurs, such as in the case of a redundant farm building into a residential dwelling where contemporary building regulation standards need to be sympathetically satisfied,” says Samuel. Hempcrete absorbs moisture from the air when humidity levels are high and releases them once levels drop. “These amazing properties become very important both in retaining the fabric of a building in good condition and also assisting with the health and well being of their occupants,” says Samuel. Made entirely from natural materials, it is fire and pest resistant and is a “better than zero carbon” material because it has a negative carbon footprint. Its exceptional eco-credentials make it an obvious choice to “significantly reduce your energy bills” and “the overall impact of your building on the environment,” says Samuel. “This, together with its hydroscopicity, renders hempcrete buildings extremely healthy living environments to occupy as residences or places of work,” he explains. Replenishing itself in just four to five months, hempcrete can be considered to be truly sustainable, says Samuel, and once set it creates thermal mass and insulation due to the density of the lime binder. “Hempcrete is able to store heat in the

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