How better acoustics creates more sustainable buildings
Buildings increasingly have un-openable windows to combat the challenge of noise pollution but mechanical ventilation increases energy consumption – how can acoustics resolve this clash?
Report from – Ze Nunes
Image: AHR Architects
Almost half of the world’s population lives in a city, and for many people noise can be a serious issue, indeed the World Health Organisation states traffic noise is harmful to the health of a third of Europeans.
In noisy environments buildings will often be mechanically ventilated and windows kept shut, but this can double a building’s (summertime) energy consumption. So how do we overcome the clash between a building’s acoustic and ventilation requirements – and what are the challenges and benefits of sustainable acoustics?
Acoustics are invisible, complex and often seen as a ‘dark art’ by design teams. To explain acoustics better, we developed in-house software to model and crucially to visualise how sound and air flow through windows and acoustic air vents in a building.
Being able to ‘see’ and hear the sound in a building before it is constructed makes it easier to understand acoustics and collaborate with acousticians. Design teams can then assess the sustainability and effectiveness of various noise mitigation solutions for open windows and vented facades.
Limited performance data
The lack of acoustic performance data for windows and vented facades is a challenge when designing sustainable buildings. Current guidelines state the sound reduction offered by open windows is 10-15dB, but Napier University has shown sound reduction is 23dB when the correct window design is chosen. Better performance data means more buildings can be naturally ventilated, as shown in the noise maps below.
Image: MACH Acoustics
Overcoming ugly, bulky attenuators
Cross ventilation is the most effective form of natural ventilation, with the important advantage that air inlet vents can be 25-75% smaller than those required for single sided ventilation, reducing noise break-in.
Attenuators are necessary to enable air to flow between work spaces or rooms without sound transfer but can be unsightly, expensive and bulky. MACH Acoustics created the Honeycomb Attenuator to offer architects a simple, low-cost means of enabling natural and cross ventilation in a building. Cut from acoustic foam, this cheap and flexible attenuator is unobtrusive and saves on space. A benefit of this design is its easy implementation of heat recovery in winter, with the attenuator offering very little air resistance and reducing energy.
Image: MACH Acoustics
So how can acoustics reduce a building’s carbon emissions?
Noise mapping and building orientation
A building’s position, orientation and U-values will all impact the size of ventilation openings in a façade, so a holistic approach is needed to achieve a low carbon design.
When deciding upon orientation, a noise map will help maximise a building’s efficiency in terms of acoustics and ventilation. Using maps created from massing drawings at an early stage, quick, cost effective modelling will give architects the facts about a site’s noise levels to make an informed decision about a building’s form, position and orientation. Noise maps can then establish exact noise levels at each of the façades and even at individual windows. This allows non-critical spaces, such as corridor walkways, to be located on the noisy side of a building, so creating an acoustic buffer.
Cross ventilation will be effective when the air intake is placed on the quiet side of the building, or single-sided ventilation can work for sensitive spaces on the quiet side of a building. Careful consideration of the acoustics together with ventilation at an early design stage will therefore significantly enhance the sustainability of a building.
The future of windows and air vents
If noise ingress is not sufficiently reduced by windows, innovative window design is needed to enhance existing sound reduction. If even higher attenuation is required then an attenuated façade will allow for natural ventilation on almost any site.
Looking ahead to the future, our research at the University of Bath’s construction materials test facility, the Building Research Park , near Swindon, is exploring the optimum window or façade designs to minimise external noise ingress in low carbon buildings. In addition, through modelling, we have also researched how balconies in high-rise residential accommodation could dampen noise reverberation caused by street canyons.
Building usage and embodied energy
A building’s usage affects its energy efficiency and while poor acoustic design can limit a building’s layout, good acoustics can enhance the layout and enable air flow through interconnected, open plan spaces such as atriums and light wells, managing noise ingress and transfer through these spaces. In this way, acoustics will increase a building’s efficiency and minimise wasted space/materials, so improving both the building’s functionality and its sustainability.
Beautiful buildings and new construction materials with lower embodied energy also bring new issues for acousticians – for example, cross-laminated timber (CLT) buildings are sustainable and yet acoustically very poor.
Case study - Keynsham Civic Centre, Somerset
The award-winning Keynsham Civic Centre, a public library, with retail and office space, demonstrates how acoustic design helps enable an almost zero carbon building.
Created by AHR Architects, it is one of the most energy efficient public buildings in the UK, with its awards including a RIBA South West & Sustainability award, BCO Best Corporate Workplace and CIBSE ‘Project of the Year – Public Use’.
This light and airy building, located on a busy arterial road, required considerable input to ensure good open plan room acoustics, to prevent noise ingress through the naturally ventilated façade and also to allow cross ventilation of the open plan office space, with its interconnecting atrium and voids.
Image: AHR Architects
The architect commissioned MACH Acoustics to map and establish noise levels across 25 different elevations. Auralisations via 3D acoustic modelling were also carried out to study the passage of sound in the building, plus analysis of materials, furniture, wall and ceiling treatments.
Careful acoustic design enabled the architect to naturally ventilate this building, addressing the poor sound insulation of its beautiful, low carbon CLT design, successfully integrating acoustic treatments and lowering the building’s overall operational energy use to help achieve a targeted DEC (Display Energy Certificate) ‘A’ rating.
Ze Nunes is Managing Director of MACH Acoustics, which provides acoustic consultancy across all areas of the built environment.