Roofconsult Website Rainscreen Cladding by Mike Smith of Eurofox Engineering Ltd

The principles

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  • A Rainscreen system consists of an outer panel, a ventilated cavity and an inner leaf
  •  In driving rain conditions moisture forms a membrane across the baffled vertical and horizontal joints
  •  The majority of water is deflected off the outside face - any penetrating water is disposed of through drainage
  •  Rainscreen systems differ from brick wall sealed construction as the beneficial effects to air movement are utilised
  •  A Rainscreen system is ‘pressure equalised’ - the joints are open or lightly baffled, allowing pressure equalisation in driving rain conditions to be instantaneous. Pressure inside the cavity is equal to pressure outside - ie, precipitation has no inclination to be driven into cavity
  •  A continuous vertical cavity – Usually min 30 mm or for NHBC schemes 38 – 50 mm
The advantages
  • Installation is simple - allowing external cladding and internal works to proceed speedily, early and consecutively
  •  Problems of deterioration are halted with minimal additional load being applied to the existing structure (referred to as Overcladding)
  • Rejuvenation of external appearance
  • Use of dry trades not wet trades – Modern Methods of Construction
  • Energy saving - lower running costs due to greatly improved thermal insulation
  • Easily removed panels for monitoring of structure
  • Reduction of the risk of condensation due to the elimination of cold bridges
Combinations of cladding are increasingly popular – This creates challenges when designing the support system. The skin or façade of a building is one of its most distinctive elements. Behind every beautiful façade is a support system which has been engineered to suit that particular building’s conditions, from its geographical position and its height to its structural material and the weight and size of its cladding panels.
The basics
The weight of cladding elements can vary enormously from a modest 5.6 kg per m2 for composite panels up to tile materials weighing in at c. 110kg per m2. The building’s location is of key importance too due to wind loading; an exposed coastal site will be very different to a low rise city centre project.
These factors are of key importance for determining the support system for the façade, but then that can have a knock-on effect on the main structure of the building, particularly with light weight steel framing which may be reduced – or alternatively beefed up – as a result of the cladding and the way it is attached.
A simple cladding support system typically consists of ‘helping hand’ brackets, which are fixed to the substrate at set vertical, and horizontal separations. Into these attach profiles, usually vertical ones, which are often an ‘L’ or ‘T’ shape in section, although they can be more complex to accommodate different cladding panels.
Cladding may be visibly face fixed, normally riveted onto aluminium support profiles. Architects are currently tending to prefer concealed fixing either structurally bonding cladding elements onto the vertical support profile [see diagram A] or if the specifier requires a mechanical concealed fix then an additional horizontal grid and cleat system can be adopted
The vertical profiles attach to the brackets by a combination of fixed and flexible points to allow for dead loads and for dynamic load e.g. thermal movement. Flexible points are vital due to the differing thermal performances of the materials being combined. Take aluminium and high pressure laminate (HPL). HPL panels are made from wood pulp and resin. In the winter the aluminium will be at its minimum length, whilst the HPL will have taken on water and will have expanded. In the summer, the reverse is true. Aluminium expands by 1.0 mm per linear m per 100 degrees C and in the UK temperature could vary from -10 degrees C to 40 degrees C or possibly more.
There are certain key elements that a façade support system specialist needs in order to design a system. First the type, weight per m2 and intended layout (portrait or landscape) of the façade material. Second the preferred fixing method: whether concealed or visible fix. Thirdly details about the building, its height, window heights and its geographical location (in order that wind loads can be determined). In addition it is essential to understand the type and condition of the substrate to which the system is to be fixed (steel or block / masonry), depth of insulation and the overall cladding zone (including the correct ventilated cavity)
From this basic information, a specialist façade engineer can calculate the type, ‘mix’, the optimum horizontal and vertical spacing of brackets required for the bulk of the building and also for more extreme conditions / special areas (such as corners and under windows). Fixed point brackets must be able to withstand the weight of the cladding panels and the wind suction, whereas flexible point brackets have only the wind suction to withstand. The spacing of brackets required will vary depending on the area of the building. Generally more fixings are required at the edges and corners of buildings and around window openings.
Often the architect’s specification will consist only of the support system type and some basic information about bracket spacing, or in some cases there will be no mention of a support system. Some clients or contractors choose to employ a specialist envelope designer to ‘fine tune’ the design and layout
When assessing a tender from a specialist contractor, package managers need to be aware of a number of things.
Check that the support system has been engineered to BS 6399-2 which covers wind loadings of buildings. Make sure that the architect’s aesthetic intent can be achieved, for example by concealing the fixings.
The major practical consideration for contractors and installers is ‘buildability’ - Will the size of the panel allow it to pass through the scaffolding? An architect may envisage a large ‘monolithic’ panel - 3.6m by 1.2m. The panel could weigh 130kg each. If you’re installing that on a windy day with a tower crane, you will struggle so panels may need to be split down to assist with installation
Control of heat loss is of key importance, particularly since the introduction of the  Part L and the drive towards carbon neutral buildings. Procurers should check that the detailed design allows the thermal requirements to be met. For example check that the system limits thermal bridging by the inclusion of insulation pads which sit between the bracket and the structure prevent. (These pads also prevent a chemical reaction occurring between an aluminium bracket and lime in a cement frame)
By the time a cladding package is being procured, the type of cladding may have changed from what the architect originally specified. In these situations it is important to check that the calculations which determined the type and design of support system still hold true.
The situation may arise that a cheaper cladding material has been specified, but that it is heavier than the original. In this case larger brackets or closer spacing may be required. Alternatively, if the material is lighter, a lesser system may be sufficient. This will lead to some savings in material and possible savings in time if there are less fixings or a simpler support system.
Eurofox On site
When it comes to the installation stage, one of the biggest challenges faced by systems suppliers such as Eurofox is short lead times. Specialist contractors are unwilling to invest in materials until they are certain that their section of works is about to begin. Preplanning which allows contractors to have a certain start date and therefore give suppliers a reasonable lead-time helps here.
Tolerances are also an issue at this stage, since the cladding system must accommodate a steel or concrete structure which is not bang on. Here a support system which can cope with potentially large differences is very helpful. Eurofox can accommodate cladding zones from 40mm to 380mm in 1mm increments. Systems are designed with a factor of safety .If tolerances are far outside specification, it may be necessary to check the calculations to ensure that additional brackets are not required. Package managers should also check that the correct materials and components are being used. For example, stainless steel screws are required for aluminium because a galvanised steel screw would cause the aluminium to corrode. It is also important to check that inferior products have not been substituted, as these may not have the traceability of the originally specified component. Aluminium systems should be manufactured in accordance with
In conclusion
There are no set standards for procuring cladding support systems. Every application is different and requires some engineering input.
Systems, which are simple and logical to use, will lead to less errors and swifter installation. Cladding is a serious business – Support systems need to be ‘fit for purpose’
Eurofox can be contacted on 01707333396
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