Archive 2016 08

Modern Methods of Construction 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.” n 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 insitu 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. n ADVERTORIAL Polarwall launch Floating Factory concept POLARWALL have recently launched their new mobile Offsite Construction concept which is being called the Floating Factory and which is starting to attract interest from some of the larger developers and housebuilders. Polarwall director Alan Wheeler says, “Everybody is aware of the advantages of offsite construction but there are plenty of problems that can be caused by manufacturing in a remote location. Delivery delay issues, wrong sized or misaligned panels and the loss of control over the whole build process are just some of the issues that can arise. We think that by bringing the factory either on to, or close to the site then we can give the best of both worlds – it’s a sort of Onsite/Offsite hybrid method that we call the Floating Factory. This is a process that lends itself to larger building sites where lifting gear is available” Using the assembly jigs, the Polarwall Insulating Formwork is built into large panels of 2.5m wide by up to 3m high. These panels are then taken to the required position on the site and joined together into full wall assemblies. One builder, who is currently building a large apartment block in Berkshire, is gang-forming several of these panels together and then lifting the whole wall into position. Interestingly, the company have just done a large basement project in West London where the panels were made and lifted into position with the reinforcement in place, and this proved very quick and cost effective for the contractor. Several contractors who are looking to use this building technology are also looking at options for using a mobile batching plant on the site. This can give huge savings on the concrete cost and more importantly bring the concrete production under the control of site management. One Polarwall contractor, Andrew Skinner told us that “Using the large panels is a very exciting development for us. We have used the Polarwall formwork almost exclusively for the last three years. It is already an impressive construction material and cost effective build method, but by using the large panel assembly we have moved this up a gear and the build speeds are becoming incredibly quick.” The Berkshire site is based in Slough and it will be having a number of open days for interested parties. Anybody who would like to visit and speak with the contractors and project management should in the first instance contact Polarwall (01392 823300 or [email protected]) to arrange. www.builderandengineer.20

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