Designing acoustically-effective façades
The smooth and shiny façades on contemporary high-rise buildings certainly look sleek, but they are a significant factor in city noise because of the way they reflect sound. Doctoral candidate Jochen Krimm is calling for façades with more structure and mandatory acoustic testing for every high building.
Krimm’s doctoral research reveals that airtight, smooth façades made of glass, metal or stone can double the intensity of traffic noise. “Façades act like loudspeakers and designers are completely ignoring the noise impact”, says the doctoral candidate. “This has to change.” His years of experience as a sound engineer play a role in Krimm’s interest in acoustic reflection from façades. Why do we attempt to regulate indoor noise, but consider constant noise around high-rise buildings to be totally acceptable? The design of façades should take other factors into account and not just transparency, temperature regulation and maximising lettable floorspace. Krimm: “You would never start building without first testing the load-bearing capacity of the ground. Since any new building always has an acoustic impact, it should always be tested beforehand.”
A façade that has a sound-dampening effect also improves the building itself. After all, how can you position the bedrooms in a quiet part of the building if no such part actually exists? We not only need to consider the transmission of sound from outside to inside, but also from outside to outside, argues Krimm. Failure to take action soon could soon leave our increasingly built-up metropolises with no quiet places left at all.
The literature and laboratory research conducted for his thesis, entitled 'Acoustically effective façades design', reveals that noise reflection via the façade is relatively easy to control. A structured surface can reduce environmental noise by around 3 dB, according to tests on models on a scale of 1:50 and 1:100. Additions such as balconies and blinds also make a significant contribution to noise reduction. If blinds are already used to protect against the sun, they can also be given a second purpose, to reduce noise. The same applies to solar panels. Tiled façades from the 1970s appear to respond relatively well to exposure to noise.
A typical indoor solution, such as perforated sheeting, is not feasible for outdoor façades because of the maintenance issue. However, positioning façade elements at a slight incline to each other can provide a solution. This enables the noise from cars, aircraft, pile-drivers and motorbikes to be dispersed over a wider area. Krimm believes that architects should make greater use of this tool in the design of buildings. Does this not considerably increase the cost of façades? “It's slightly more expensive, but the method does not need to be applied to every façade”, he explains. “The approach adopted for a façade along a motorway is different from one next to a park.”
Every building is designed for a specific location and the acoustic design is part of that process, he argues. He calls for standard on-site noise tests and tests in a sound chamber using a 3D model or mock-up of the façade.
Jochen Krimm is already in talks with developers on building a pilot façade. This will aim to demonstrate that an 'acoustically responsible' façade can help improve the design of the urban environment.
Thesis defence Jochen Krimm
5 July 2018 12:30 - Aula TU Delft