SpecifiedBy EditorRainscreen cladding is an innovative cladding technique originally developed in Norway in the 1940s and 50s.
The principle behind rainscreen cladding, sometimes called ventilated cladding or just rainscreen, is having multiple layers in the external wall of a building, each performing specific functions, instead of a single layer acting as structure, thermal and acoustic insulation, and moisture and wind barrier all at once.
Because the outer ‘rainscreen’ layer is just the wall’s first line of defence against wind and water coming into the building, it does not have to be completely sealed or waterproof, but rather acts as a screen to prevent most water and wind from entering the building envelop.
Technical Details for Rainscreen Cladding
In a rainscreen system, the external cladding itself is not the waterproof element, but rather acts as an outer skin, a shield to protect the actual waterproof membrane or sheathing behind it, as well as providing a narrow air gap so that water can drain and evaporate off the inner wall.
Similarly the rainscreen doesn’t function as structural support or as thermal or acoustic insulation, but just as an aesthetic and physical barrier which protects the waterproof membrane from excess water and wind, because it will never be 100% waterproof, and from sunlight, which causes such membranes to degrade over time.
In fact, there are two variations of rainscreens which are often confused, and function in slightly different ways: drained/back ventilated and pressure-equalised. Both of these variations are often referred to as ‘open-jointed rainscreens’, though unsealed joints between panels can only be a feature of drained and back ventilated systems.
Drained and Back Ventilated Systems
Drained and back ventilated rainscreen cladding systems have drainage and ventilation gaps at the top and bottom of the wall, with a single ventilated cavity running the full height of the wall. This variation assumes that water will get behind the outer rainscreen into the cavity, and thus allows the water to drip down the waterproofed face of the inner wall and drain out of vents at the bottom, as well as creating a current of air from bottom to top to help evaporate water and keep the cavity dry. This type of rainscreen is more common on small to medium sized buildings.
Pressure-equalised Systems
Pressure-equalised rainscreens are more complex, and have individual cavities and drainage gaps at the bottom of each rainscreen cladding pane. They were developed to counteract the effect of high winds driving water into the facades of tall buildings, and are still mainly used in this context. In this variation of rainscreen cladding, the function of the airgap between the outer rainscreen layer and the inner waterproof layer is to equalise the air pressure in the cavity with the outside; this helps to wind-driven rain from penetrating the outer, rainscreen layer. Any that does can drain out of the gaps at the bottom of the panel.
Note: This article focuses more on the common drained and back ventilated rainscreen cladding systems mentioned first.
Specification of Rainscreen Cladding
Correctly specified, rainscreen cladding systems will provide insulating properties whilst controlling water, wind and fire.
With both types of rainscreen cladding systems, it’s important as a specifier to understand where these vents will be, and how they will affect the look of your external wall.
Rainscreen cladding requires very careful design, detailing and installation, particularly at building edges, and where doors and windows broach the facade system. Tolerances tend to be lower than with other building elements, in part because mistakes will be so visible, and in part because rainscreen cladding is almost invariably manufactured off site.
Rainscreen cladding is usually a proprietary system of panels and fasteners patented by the manufacturer rather than just the panels alone, and in some cases must be installed by an appropriately certified professional due to the enormous variation in fastening mechanisms and their complexity.
Rainscreen cladding is essentially a form of curtain walling: each panel hangs from its own fastening, or a vertical support rail, on the structural wall behind, with various ways of fixing the fastenings without piercing the waterproof layer which covers the inner structural wall.
Sometimes, waterproof, foil-covered rigid insulation is added to the outer face of the inner wall, because this is often the most advantageous place for it in the wall build-up to reduce cold bridging.
Advantages of Rainscreen Cladding
The greatest advantage of rainscreen cladding over other types of cladding, which are usually called ‘face-sealed cladding’, is its extraordinary flexibility and the diversity of options available.
Because the external, visible, rainscreen layer of the facade doesn’t have to be fully watertight, it can be made out of almost any material imaginable finished with any texture or colour. Commonly used rainscreen cladding materials include glass, stone, aluminium, ceramic, cement and timber, with an endless variety of different options to choose from, and thousands of different manufacturers. In addition from this complete aesthetic flexibility, rainscreen facades are also very adaptable to different wall shapes such as curves. Rainscreen cladding can also be made from recycled materials if you’re looking for a sustainable cladding option.
Rainscreen facades are very robust compared to other building systems, usually coming with a lifespan guarantees from their manufacturer. Because rainscreen systems are inherently modular and made up of individual panels, if there is a problem with a single panel, it can be replaced with relative ease and at minimal cost. Maintenance is very minimal for rainscreen facades, with the materials commonly used never requiring repainting or resurfacing, making for a lower cost over the entire lifetime of the building. Indeed rainscreen cladding systems are now considered to have superior weather-tightness to other cladding systems, and this is reflected in their increasing use in the building industry.
Finally, rainscreen cladding benefits from extremely fast install times compared with other cladding systems, and this is especially useful in busy urban settings. Cladding work can even go on once the building is occupied, as it is merely external and does not cause significant disruptions to the functioning of the building.
Common Use Cases for Rainscreen Cladding
Rainscreen cladding is commonly used on larger buildings due to its efficiency in construction, but occasionally on single-family homes and other small buildings as well. Its superior performance and aesthetics make it a very popular choice for architect-designed buildings, particularly in wet countries, and where performance is required. Rainscreen cladding does not necessarily have to be expensive, and there are a wide range of price points to choose from.
How To Choose a Rainscreen Cladding System
Once you have decided to specify a rainscreen cladding system, you’ll want to choose based on the availability of whatever material, colour or finish you’re after. But there are other, equally important factors to consider.
Perhaps the most important is the system’s performance and the guarantees the manufacturer gives for its product. You should be asking questions such as:
- What lifespan does the system have?
- What kind of guarantee does the manufacturer offer?
If possible, it’s always a good idea to go and visit a building with the cladding system you’re intending to use to see its performance in the real world. Otherwise, reading reviews here on SpecifiedBy, or asking other architects who have specified the system in the past is highly advisable.
Another major factor to consider when specifying a rainscreen cladding system is the material compatibility between the panels and the structural wall of your building behind it, as well as with the waterproof membrane between them. How these elements interact are the responsibility of the designer, and a successful design requires an in depth understanding of how the cladding system will be attached to the wall through the vapour barrier. The chemical compatibility of adjacent metals with sealants and membranes should be investigated with the cladding manufacturer to avoid problems of corrosion or or sealant adhesions.
Other Considerations
One of the most important things to remember when designing a building with rainscreen cladding is that water will flow freely through your facade; this means that you have to think extra carefully about where that water is going to drain out, and what it’s going to drain onto. Time and time again, we see beautiful rainscreen cladding stained with rainwater discolouration because the specifier hasn’t thought carefully about where the water will go.
This is particularly true in problem spots such as building edges and corners, roofs and parapets, and really anywhere else where water might collect. Similarly, the cavity behind your rainscreen must have the appropriate width, relative to the building’s height, to allow water to drain as well as evaporate.
Regulations to Consider When Specifying Rainscreen Cladding
There are no current regulations directly addressing the design and installation of rainscreen cladding of either type. The Building Regulations do make reference to the Code of practice for design of non-loadbearing external vertical enclosures of buildings, but this was published in 1985 and has not been updated since, thus making it obsolete for current rainscreen cladding systems.
Despite this lack of guidance, other more general regulations do relate to the structural, thermal, and fire performance of rainscreen cladding.
Structural performance of panels, requiring that they be able to hold their own weight, is covered by BS EN 14019 (2004) ‘Curtain walling – Impact resistance – Performance requirements and BS EN 13116 (2001) ‘Curtain walling – Resistance to wind load – Performance requirements and calculations taking account of rails, fixings, and rainscreen panels are often necessary to demonstrate suitable structural capacity in the advent of high winds. Fire resistance is dependent on the structural wall holding the rainscreen, the performance of which is covered by Approved Document B.
Similarly, fire stops between the building envelope and interior compartments, as well as cavity barriers at edges and window openings, are required by the same document. Thermal performance is covered by Approved Document L in the same way as other wall constructions.
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