Building the modern way

Firms are embracing new methods of construction with a study revealing the majority have used innovative techniques in the last three years. Claire Cameron takes a look at what is on offer

ACCORDING to the National House Building Council’s 'Modern Methods of Construction: Views from the Industry' report, 98 per cent of the 135 large and medium-sized house builders surveyed are attracted to MMC's perceived faster build ability with many believing the method has a role to play in improving the quality of construction, overcoming current skills shortages and increasing output.

New techniques like single-envelope cladding and concrete canvas are increasing in popularity, while straw and hempcrete are perhaps two of the more unlikely construction materials.

Ex-Straw-dinary creations

Firms should consider building with straw because "it's the material of the future," says Barbara Jones, director of natural building specialists Straw Works.

"It is structurally strong, very durable, highly insulating, and can provide buildings to a passive house standard if required."

Based in Todmorden in Yorkshire, Straw Works has been involved in the creation of more than 300 residential and commercial buildings using straw bales and natural materials. These include EcoHub at Lordship recreation ground in Haringey, a terrace of two loadbearing straw houses in Elmfield and the strawbale kitchen at The Outback Centre in Calderdale.

Best used as a wall building material, as insulation in walls, floors and roofs, or as a fibre binder in clay plaster, the agricultural by-product can also be supplied as pre-fabricated panels (e.g. Ecococon, Modcel) which can speed up build time and provide exact costs for delivery and installation, explains Jones.

And putting aside the "flat and very regular" pre-fabricated version, straw “is beautiful and organic in shape and texture,” says Jones.
There are four ways to build with it – loadbearing, infill, hybrid and pre-fabricated panel.

“Loadbearing has no frame so straw 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 factory-made 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, energy-efficient, 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.

CASE STUDY: 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.

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 Yorkshire-based chartered architects, Samuel Kendall Associates.

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 fabric of the material, acting like a giant storage heater,” explains Samuel, who says this has two advantages.

Unlike in modern buildings which are reliant upon airtightness to trap the air in the building, “it allows for natural ventilation in a building and is also able to store solar heat in its thermal mass, meaning that you are free to open a window to increase natural ventilation safe in the knowledge that your heat will not just flow out and be lost,” he says.

"Secondly, the slow speed at which hempcrete stores heat and releases it results in ‘buffering’ natural changes in temperature,” which results in relatively even internal temperatures being maintained.

As a fairly unknown building material, hempcrete can be tricky to work with at first and you will need to have some “patience initially, given it is so different to accepted construction methods,” says Samuel.

And builders looking to use it for the first time should “visit existing buildings that employ the use of hempcrete in their construction and observe the techniques used in both the design and detailing.”

CASE STUDY: Insulating with hempcrete at Baswick Steer

WHEN a group of farm buildings at Baswick Steer in Holderness, East Yorkshire were converted into residential use, the owners’ success in the growing of hemp led to hempcrete being used as the insulation material.

Despite being constructed in the 1800s, the buildings were in sound structural condition and could be altered without excessive change.
In order to establish a satisfactory thermal mass to this “Deep Green” development, the Hempcrete was mixed on site and applied as an external insulation layer over the existing brick structure. The 250mm thick layer of hempcrete was laid in-situ in 150mm thick vertically tamped layers and finished externally with a traditional lime render.

This ensured that the dew point thermal curve through the external structure was satisfactory and that no interstitial condensation is likely to occur within the structure.

The potential heat loss through the external envelope of the converted buildings well exceeds the minimum requirements for “U” value, thereby further reducing the need to heat or cool the internal environment.

The buildings were further insulated with hempcrete at pitched roof level using Hempcrete in the form of a “warm deck” construction, which eliminates the need to ventilate any roofspaces.

Driving single envelope construction

Single envelope cladding is one of the latest in a series of new innovative designs developed for warehouse and distribution facilities. Tony Wall, managing director of composite panel construction specialist ISD Solutions explains

THE requirement for low cost, ultra-modern and virtually airtight cold store and warehouse solutions has seen a step change in design and building practice with insulated composite panels and single envelope construction fast outpacing traditional building methods.

With rising energy costs and ever tougher efficiency targets, it’s hardly surprising. By applying smart design, expert delivery and proven know-how, ISD says cost reductions of up to 20 per cent can be achieved whilst delivering virtually airtight, high-performing buildings with low lifetime running costs.

Build time is also 20 per cent faster than conventional methods and the strength and spanning characteristics of composite roof and wall panels significantly reduces the requirement for secondary steelwork.

Single envelope cold storage requires an estimated 30 per cent fewer raw materials and can also deliver significantly lower long-term running costs due to increased thermal efficiency and air tightness.

The reduced Global Warming Potential (GWP) of modern composite panels can also help meet WRAP and BREEAM targets.

Recent completed projects include facilities for Aldi, Morrisons, Costco and M&S which have all benefited from composite panel construction.

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."

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