1. What is Rainscreen Cladding ?
Rainscreen cladding is a series of components forming a system to act as a protective weather-resistant barrier to a building. The cladding consists of a decorative skin fixed to an underlying structure by means of a supporting grid. The supporting grid or ‘framing system’ is attached to an airtight backing wall and forms a capillary break. The materials used for rainscreen vary but the principle is to protect the backing wall from direct rain, allowing the majority of wind blown moisture striking the external face of the cladding to be thrown off. However, any that manages to penetrate the line of the cladding will be dissipated in the purposely designed ventilated air cavity directly to the rear of the cladding panels. Ventilation is fundamentally obtained at the base and head of the cladding.
The finite build-up of the rainscreen and relevant components can be tailored to meet project specific criteria deemed necessary by the design team and or other involved parties.
2. Why use Rainscreen ?
- Aesthetics – The inclusion of rainscreen gives the almost limitless versatility of materials and finishes, thus giving the designer freedom to express themselves in a manner appropriate for the building in question and its surrounding area.
- Low maintenance – Depending on materials used, rainscreen is a low or even maintenance free solution. Furthermore, any damage that may occur to the building can be easily repaired by replacing individual components.
- Protection – Rainscreen provides a robust protective barrier to the building, significantly slowing down deterioration and prolonging the building’s life span.
- Sustainability – Not only can responsibly sourced materials be used in the construction of rainscreen but the inclusion of insulation can be used to improve the thermal efficiency of the building, giving a lower carbon footprint, minimising energy costs and reducing scope for condensation and damp.
- Lightweight – Particularly with the use of aluminium, rainscreen is a lightweight solution, putting less strain on the building which can be a major benefit on refurbishment schemes where additional loads where not incorporated in the structure’s original incarnation.
- Soundproofing – The additional layer that rainscreen cladding enhances the buildings overall acoustic performance which can be particularly beneficial in urban area where traffic noise can be problematic.
3. Summary of Document B – Fire Safety (Approved Government Document issued 2010)
When considering appropriate construction materials for the exterior cladding of a building, guidance should be sought from Approved Document B of the Building Regulations 2010, relating to fire safety in building other than dwelling houses. This document is freely available online
The document should be read in its entirety, though Section 12 is the most applicable when looking at cladding in multi-storey buildings. Section 12 offers guidance on material selection with respect to fire ratings on various building heights. An extract of Section 12 is shown below.
On buildings 18m tall or above (from ground level) external walls should either meet the guidance detailed in the document (sections 12.6-12.9 and diagram 40) of a minimum of Class 0 fire rating or meet system performance outlined in separate BRE report (BR 135).
Insulation product, filler material (not including gaskets, sealants and similar) etc used in the external wall construction should be of limited combustibility, see Section 12.7 and Diagram 40.
4. BCA Technical Guidance Note 18
(Guide and not regulations)
The Building Control Alliance is an industry group made up of representatives from organisations directly involved in building control in England and Wales.
Members include the Chartered Institute of Building, the Chartered Association of Building Engineers and the Royal Institution of Chartered Surveyors – and professional associations promoting public and private sector building control, Local Authority Building Control and the Association of Consultant Approved Inspectors.
In 2014 the BCA issued the following guidance in relation to buildings exceeding 18m in height.