How rainscreen façade can offer acoustic benefits

Acoustics in building design

Noise pollution is becoming an increasingly major issue as our cities are interwoven with roads, railways and air traffic. Due to the scarcity of land, development near such noise pollution is sometimes inevitable in order to expand current housing capacity. Any new development in the presence of existing buildings must be evaluated in relation to noise levels and this applies both ways. Noise generated during construction to surrounding buildings and later noise generated by surrounding sources to your building. Poorly designed buildings, or those that underestimate the importance of acoustics of the building envelope, can lower the value of the entire property in future. Anyone who has lived close to a busy road will know acoustic well-being is key to the quality of life of occupants.

Future disputes regarding outside noises and evaluation of it is measured according to code BS4142 that compares new noise to the background noise levels. For example, nearby construction site might have limited working hours due poor acoustic insulation of adjacent building.

To make sure that acoustic requirements are met, measurements are taken on site, a point at which the potential costs of fixing any issues identified are highest, therefore acoustics as a whole needs to be taken into consideration in the early stages of project preparation.

General acoustic requirements are currently defined in the UK by Approved Document E. In the document, you can find all the requirements both for single dwellings, residential and special requirements for schools (Schools have also separate and more strict code BB93). Most of the document focuses on internal walls separation in-between dwellings.

Approved Document E page.8

The second document related to this topic is code BS 8233:2014 Guidance on Sound Insulation and Noise Reduction for Buildings. This code follows closely the World Health Organization recommendations on maximum indoor ambient noise level targets for spaces within buildings when occupied, with the aim of providing a preferred level of acoustic comfort in commercial premises and suitable conditions for resting and sleeping in residential accommodation.

Table showing sound levels with examples. Notice that our perception of how “loud” something is, is not linear and 70dB noise will seem to us twice as loud compared to 60dB.

This shows that every single decibel of sound resistance counts!

The third sets of requirements can come from either BREEAM or LEED certification. Both evaluate sound resistance and give appropriate credits if you go beyond the standard government requirements.

Acoustic performance of building envelope in general

The acoustic performance of the building envelope as a whole, is determined by two key parts:

-       Windows, doors and other openings are weakest points of façade

-       Connections to slabs and other details

-       Façade itself as it has largest surface area exposed to outside

In terms of acoustics of façade we further look at two main criteria:

Sound absorption and reverberation – tells us how sound reflective the façade is or isn’t. This is heavily dependent on the material characteristics of the surface finish e.g. cladding and it’s fixing method to the substructure. In other words, sound reflective façade, combined with shape that multiplies this effect, can cause noise from the street to bounce back on the street and negatively affect pedestrians.

Sound resistance (Airborne sound insulation) – In decibels [dB] how much noise the wall blocks from the outside.

Sound resistance is further described by two values in UK:

DnT,w [dB] – Is on-site sound resistance. Measured when the wall/façade is completed and how to exactly measure this is described in Approved Document E. All government requirements are compared to this value.

Rw (C; Ctr) [dB] – Is weighted laboratory sound resistance with corrections (C; Ctr). As the name suggests, its measured in a laboratory under ideal conditions on a large scale sample. Ideally DnT,w (on-site sound resistance) value is within range of those corrections, meaning that the structure is installed correctly. It can be issued for a single material (e.g. concrete, brick, mineral wool) or an entire structure, here the concrete wall combined with ventilated façade. Rw is our main lead in early project phase to make sure that DnT,w later passes the requirements.

Testing chamber with Hilti ventilated façade installed and ready for the test Rw (C; Ctr).

Hilti’s research into sound resistance of rainscreen facades

Ventilated facades are gaining popularity among architects and contractors due to its range of benefits like thermal efficiency, longevity and vast aesthetic possibilities external cladding brings. Its non-homogenous nature however, makes fully understanding sound resistance of ventilated façade hard and because of this complexity its benefits were often overlooked. That’s why Hilti Eurofox partnered with panel producers, insulation producers, acoustic specialists and the University of Vienna to participate in a project with one goal in in mind. To find out exactly how much different types of cladding, insulation and substructure add in terms of sounds resistance.

Over the course of this project Hilti tested several different configurations according to EN ISO 10140-1;-2 and along with them developed mathematical tool to calculate Rw value for any type of cladding or wall configuration. These are the results.

ΔRw,direct [dB ] is increase in sound resistance with façade compared to plain concrete wall without it.

Example of the measurement protocol with results.

Based on the results there are several interesting points:

- Ventilated façade with insulation, substructure and external cladding always increases sound resistance. This might seem obvious, but ETICS façade according to ETA guidelines if not tested lowers sound resistance of a wall by -8dB. Tests of mineral wool show small improvements of 1- 3dB and cheap EPS insulation can even lower the sound resistance of exterior wall!

-  Improvement of sound resistance of original wall with Hilti ventilated façade goes from 9 to 12dB based on type of cladding and insulation thickness.

- Heavier cladding doesn’t automatically mean better sound insulation. We can guess that at certain point stiffness of the substructure takes over and starts to play a role.

- Ventilated façade provides very good sound resistance thanks to its non-homogenous structure and diversity of materials in each layer. Thus, covering wide spectrum of sound frequencies.

- Weakest point of façade as a whole will always be windows and doors (typically in range of Rw=35-45dB) and their connections. To get full assessment of façade sound resistance, all parts of façade need to be included in detailed calculation model.

Thanks to this, Hilti can now offer you Rw (C;Ctr) calculation with any type of cladding for your project. This allows you to evaluate the acoustic performance of your project beforehand and include it in your BIM model. Using our engineering services, you will get the most out of your ventilated façade and the extra sound resistance it brings.

Our comprehensive service offering includes:

-       U value calculation and wall thickness optimization

-       Cooperation with multiple cladding suppliers

-       Cooperation with insulation manufacturers

-       Cooperation with installers

-       Design and supply of façade substructure

-       BIM design and support

-       Façade fire safety consultation

-       Structural design

-       Sound resistance, calculation of Rw (C; Ctr)

To get in touch with our façade consultants to discuss your project specific needs, please send us an email

If you have any question related to the article or our rainscreen solutions and services, please post your question on Ask Hilti .

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This article is part of ongoing series dedicated to ventilated facades. Find more here