Rainscreen – A Brief History
You can’t go far these days without coming across a building using some form of rainscreen cladding.
From schools and hospitals, to skyscrapers and national parliaments, the solution’s versatility has made it a favoured tool of specifiers across the world. However, the story of rainscreens stretches back far beyond its modern uses; to the timber barns of ancient Norway.
It’s fair to say that the short summers and long, harsh winters have forged Norwegians into some of the world’s leading experts on the preservation and storage of food supplies (just take a look at the Svalbard Global Seed Vault). One of the greatest challenges early farmers faced was how to prevent moisture, either from the driving rain or snow, permeating into their barns and destroying their hard won harvest.
Their solution was to use a two leaf construction described as the “open-jointed barn” technique. The open joints of the wooden outer-leaf allowed air to circulate within the cavity. As a result, any moisture which passed through the first timber cladding layer either dropped through a gap at the bottom of the cavity or was wicked away by the air flowing through the cavity.
Variations in this approach were seen across a range of buildings over the next few centuries, but it was only with the advent of skyscrapers that the technique truly began to take hold. Reducing weight was a constant concern on such projects and, in the early 1950s, Alcoa decided to prove the potential of the lightweight aluminium it produced by using it to clad its new office in Pittsburgh.
The 30 storey building, designed by Harrison and Abramovitz, featured what was described as an ‘Aluminum Dress’. This curtain wall system consists of aluminium facing panels fixed to the exterior face of the inner pearlite concrete wall via anchor brackets. The thin exterior wall panels provide protection against the elements and sit proud of the interior wall; creating a cavity through which air can circulate to carry away water vapour.
Over the next decade further research was carried out by various bodies, including the British Research Station. In the early 1960s, Øivind Birkeland of the Norwegian Building Research Institute highlighted that sealing the cavity behind a theoretically impermeable outer facing created a pressure differential between the cavity and outside. As, in practice, the outer facing was never completely impermeable, this differential could drive a significant amount of water into the cavity. To resolve this issue, he proposed that the cavity be vented (essentially allowing the wind to blow in behind the cladding) in order to equalise the pressure.
Over the following decades, this “pressure equalised” approach was further refined alongside “drained and ventilated” designs which use careful detailing to channel water out of the cavity.
In the next blog in this series we’ll take a detailed look at these two approaches, and the science behind them.
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