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    Rear ventilated facades for healthy walls and comfortable buildings

    Nathan Johnson

    Also known as rain-screens and double-skin facades, ventilated facades have been used extensively across the globe by building designers looking for an extra layer of protection for the exterior walls of their buildings. 

    Similar to a tent fly, the system is essentially a pair of exterior wall skins that are separated by an air corridor and is primarily used to protect a building’s structural walls from the implications of incessant or harsh rain and wind forces.

    The major building products that make up a ventilated facade system are the support structure and the external cladding, which are separated by an air cavity and joined by anchoring elements and a sub frame. Typically, additional layers of insulation are also added to the outside of the support structure to improve energy performance and to reduce the likelihood of condensation within the wall assembly.

    Ventilated_wall_scheme.jpg

    A weather resistant membrane is nearly always added to the outside of the insulating product to protect the supporting structure from water ingress, and vapour permeable products that prevent water entry but promote vapour release are best for this application.

    Other than the external cladding, which provides the bulk of rain and wind protection, the key player in the ventilated façade system is the air corridor between the support structure and the external cladding.

    Diagram shows supporting structure (red), insulation (yellow), subframe (grey) and external cladding (orange). Image: Wikipedia

    A ventilated facade that is naturally ventilated (rather than pressurised) results in a temperature difference between the face of the cladding panel and the air cavity behind. This will in turn create a variation in air density and cause air to flow upwards within the cavity according to the stack effect. That airflow will transport heat from the cavity out through high level exhausts and can also aid convection drying of any residual amounts of water that has penetrated or bypassed the external cladding and built up within the air corridor.

    This is especially important for walls with high water absorptive claddings, such as bricks, blocks and renders which makes ventilated facades an appealing retrofit option for architects when upgrading older buildings.

    The ability of a ventilated façade to dry out is largely dependent on the air flow, the cavity’s ability to drain moisture and the permeability of the material layers adjacent to the air cavity.

    Ventilation is much more effective when applied to the entire facade and, for this reason, the air gaps that provide and expel air need to be carefully dimensioned for perfect intake and discharge along the façade.

    When it comes to choosing the external cladding element for your ventilated façade, the world is your oyster and in Australia alone we’ve seen aluminium, timber veneer and cement composite panels as well as weatherboards, terracotta tiles and glazing systems all used for the external cladding element of a ventilated façade. Recently, we've also seen integrated photovoltaics used in a ventilated facade setup. 

    Subframes are generally membrane-coated timber or, more likely, metal, and cladding is most commonly fixed to these by either screw or rivet.  Some companies also offer concealed fixings for their cladding products, which provides a more seamless aesthetic but makes it more difficult to remove panels for repair or replacement.

    Nearly all companies that advertise their products as compatible with ventilated façade systems will provide guidelines to fastening their cladding products to a support structure or subframe, some will provide specific subframes and anchoring elements.

    Here are a few products specifically designed for ventilated facades:

    INSULATION

    K15-Rainscreen-Board-Hero_edited-1.jpgKooltherm K15 Rainscreen Board by Kingspan Insulation

    Kingspan Kooltherm K15 Rainscreen Board is a high performance, fibre-free rigid thermoset phenolic insulation, sandwiched between two layers of highly reflective aluminium foil autohesively bonded to the insulation core during manufacture.

     

     

    Rockwool_edited-1.jpgRocksilk External Wall Insulation Slab by Knauf Insulation

    Available from Knauf, the Rocksilk RainScreen Slab’s lightweight and rigid properties allow for easy fixing to a masonry substrate whilst the product’s water repellant nature is an additional safeguard should rain penetrate the cladding.

     


    SUBFRAMING

    NV3a.jpgNvelope Rainscreen Cladding

    DCTech provide a range of Nvelope brackets, rails and rainscreen support systems are safe, economic and effective. They simplify the complexity of modern building facades and are suitable for the most demanding facade materials.

     

     


    WRAPS

    Enviroseal ProctorWrap by Bradford Insulation (CSR)

    Enviroseal improves the air tightness of your wall and prevents water entry, but still allows vapour to escape from inside the wall without condensing on the inside of the building frame.

    HardieWrap by James Hardie Building Products

    HardieWrap weather barrier provides a balance of water resistance and breathability, allowing moisture (water vapor) from inside your building to escape so the area within the wall stays dry.

    Sisalation Wall Wrap MD by Fletcher Insulation

    Sisalation wraps stop moisture from transferring from the external to the internal walls and allows building work to continue inside the home even in inclement weather. 


    CLADDING

    SCC_50_Kreuz.jpgVentilated Façades with building integrated photovoltaics with ERC 50 by Schueco Australia

    Schueco’s ERC 50 incorporates an external load-bearing structure that is stretched across the building structure from roof to roof. The load-bearing structure serves as the basic framework for the integration of a variety of Schueco system modules including a façade-integrated solar shading systems, building-integrated photovoltaics (BIPV) or decentralised ventilation with Schueco VentoTherm. 

     

    dekton.jpgDekton by Cosentino

    Dekton façade panels can come in large format (3200 mm. x 1440 mm) and have great flexural strength, dimensional stability and scratch resistance.

    Through connections between the cladding material and the mechanical assembly, design loads are effectively transferred back to the structural wall, providing a safe and secure façade.

     

    sah_facade-1.jpgAgrob Buchta facades by Ceramic Solutions (Aust)

    Ceramic Solution’s Curtain-type facades from Agrob Buchtal are low weight panels that can be mounted to a basic wall bracket and simply clicked into the substructure to create an even surface. In the event a panel needs to be removed (.e.g to access electrical cables or inspect concrete tunnel), a sheet metal key is inserted to unlock the panel or section, depending on the design.

     

    stringio.jpgRodeca Polycarbonate panels from Architectural Building Elements Pty Ltd

    Polycarbonate panels were used by BVN architects for the external cladding element on a portion of their double skin façade at Ravenswood School for Girls. The system uses automated louvres at low and high levels to ventilate the cavity in summer but also traps the heat in winter to retain the heat. 

     

     

    Prodema-AD-no-text.jpgProdema by SGI Architectural

    The ProdEx panels from Prodema are manufactured with authentic 100% natural timber veneer encompassing a high density bakerlite core. They are coated with a proprietary coating that is based on synthetic resins and PVDF. The panel is highly durable and protected from the effects of UV sunlight, chemical attack, and the damage caused by atmospheric agents.

     

    Trespa-Meteon-Rear-Ventilated-Facades-Ideal-for-Prolonged-Exposure-418938-l-jpg.jpgTrespa Meteon by HVG Facade Solutions

    Trespa Meteon panels can be cut to size and used as rainscreen and decorative facade, a building solution with both technical and aesthetic benefits. Joints between panels can remain open.

    The closed surface of Trespa Meteon virtually eliminates dirt accumulation and prevents paints, inks, adhesives and other graffiti materials from permanently harming the sheets. 

     

    Botanic_0002_01_SciencePyramid_Comp_web1.jpgSwiss Pearl by HVG Facade Solutions

    All Swisspearl panels are specially designed for rain-screen cladding applications with rear ventilation. This cladding system effectively protects the building and its structure from the elements for a long time. Furthermore, it reduces humidity and the air circulation optimizes the efficiency of insulation. Therefore there will be no problems like mold, fungi, etc. The rot-resistant and non-combustible panels are extremely durable and virtually maintenance free.

    EQUITONE_facade_panel_Erl.jpgEquitone façade panels

    Equitone fibre cement sheeting comes in a maximum panel size of 1.25 x 3m and can be transformed in any size or shape in the workshop or on-site. Furthermore, the material can be perforated or printed. Visible and invisible rainscreen fixing methods include riveting, screwing and bonding on metal or wood supporting frames.

     

    terracasde.jpgTerraçade TN Smooth façade tiles by HVG Facade Solutions

    Terraçade TN has been designed in consultation with Australia’s leading engineers to act as a rain screen and ventilated façade system. It is a lightweight system and is simple to install. The combination of the natural, durable properties of terracotta and the system’s modern appeal make Terraçade TN an ideal choice for architectural and residential projects no matter what size.

    452.jpgPorcelain Panels by Maximum Australia

    Maximum Porcelain Panels provide reduced water absorption, non-flammability, resistance to UV, resistant to chemical and air pollution, lightweight and limited maintenance. 

    Maximum 6mm Porcelain panels are only 14.7kg/m2 as compared to 20mm marble or granite which is approx 50kg/sqm . The load bearing weight is drastically reduced, a factor especially important in renovation works or new builds.

    103_Fachada_Femsa_OnyxSolar_01.jpgBuilding Integrated Photovoltaics (BIPV) by Onyx Solar Australia

    Building materials designer Onyx Solar has installed its photovoltaic glass as a ventilated façade of Coca-Cola bottle manufacturer Femsa's headquarters in Monterrey, Mexico. Femsa's retrofit is saving the building more than 5,500kW an hour in power, as well as reducing CO2 emission by 2.7t.

     

    5Klif.jpgDupoint Corian by CASF Australia

    The design versatility and performance features of DuPont Corian - the availability of different colours and aesthetics, custom colours, textures and finishes, the ability to shape and form the material, and its exceptional durability and renewability - have led a number of architects and designers to use Corian for exterior applications.

     

     

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