8 months ago

Total Contractor

Walls & Roofs

Walls & Roofs UNDERSTANDING DOUBLE SKIN GRID SUPPORT SYSTEMS By Jason Wood, Contracts Director at Fixing Point. Using double skin or twin skin steel insulated cladding applications is a costeffective way of improving the efficiency of a building or renewing a roof covering. The system usually consists of a profiled metal liner, a layer of insulation, a spacer system and an external metal sheet. The application of this method does, however, require consideration of a number of different factors, all of which can impact the overall stability and effectiveness of a building. Understanding the installation procedures and type of roofing and cladding system is essential in ensuring a building is secure and performs the way it should. Getting this wrong could result in multiple problems further down the line and may even require the involvement of an additional structural engineer to create a solution at more cost. Spacer systems explained The purpose of a spacer system is to provide support to the external sheet at specific points from the liner sheet. It therefore needs to be strong enough to transfer sufficient loading through to the purlins. The most common spacer system is the bar and bracket, which creates a platform for the external sheet by using steel bars. These are then supported by steel brackets attached to the purlins through the liner. Left: Work at the Logistics City project. Image courtesy of Deane Roofing Insulation Double skin roofing and wall cladding panels with a layer of insulation in between can provide additional strength and efficiency to a building. The minimum thickness of insulation for energy use compliance has, however, increased considerably over the last 30 years. This means that ensuring you have the correct insulation at the right thickness is essential for obtaining the optimum U-value. It is also very important to realise that different depths of liner sheets impact the U-value calculations. For example, installing a 32mm liner will mean thicker depth of construction is required to achieve a particular U-value than using a 19mm liner. The purlin centre spacings on a building will also affect a U-value calculation, for example 1.8m vs 1.4m. Vertical vs horizontal cladding When planning for your cladding application for roofing or walling, the most important detail to understand from the outset is that horizontal and vertical cladding require different approaches for their application. Contractors often think they can use a standard support system for any type of cladding, but horizontal cladding is, in fact, much more complicated than vertical. With vertical cladding for walls, the steel bars are fixed horizontally and in line with the purlins underneath and the profile sheet is then fitted vertically. Horizontal cladding, however, requires a 56 TC MARCH 2018

Images show the Logistics City project Fixing Point worked on with Deane Roofing, at Motherwell Way, West Thurrock, which demonstrates the use of double-skin horizontal cladding different approach as the bars must be fixed vertically, which can be a cause of confusion at the application stage. The reason for using vertical bars that span across the purlins below is so the building can handle the wind load more effectively. Although the external weather sheet is designed to protect the building from adverse weather conditions, it does also play an important role in the overall structure of a building. It is, therefore, essential that it is fitted with the appropriate support. The corners of buildings are often more exposed to higher wind loads, so when using vertical bars the spacing between them is particularly important for horizontal wall cladding sections. At Fixing Point, we recommend the use of the Gridtite General Purpose (GP) lightweight bar and bracket system for horizontal cladding. It is designed to provide a controlled space between the inner and outer metal sheets that make up twin skin site assembled roofing and walling “Contractors often think they can use a standard support system for any type of cladding, but horizontal cladding is more complicated than vertical” systems and is strong and stable when sheeted over. Using specialist systems for horizontal cladding might seem like an unnecessary expense at design stage, but it could ultimately save much more money in the long run. Because the bars are fitted vertically, a standard support system is unlikely to provide a sufficient level of security for the building and would have less spanning capabilities. A system like Gridtite GP also provides the option of pre-assembled bars, which removes the risk of misalignment of fixed brackets, and uses a single layer of quilt insulation. Contractors should, however, always take note of the capability of any GP system to accept wind suction and wind pressure loads. Thermal and structural values will also vary with every application. Contact Fixing Point 01242 265100 @FixingPoint MARCH 2018 TC 57

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