Acoustic consultant Sound Research Laboratories Ltd, Sudbury, Suffolk, UK
Acoustic design is fundamental to the quality of healthcare buildings, as sound affects us both physiologically and psychologically. Noise, or ‘unwanted sound’, can increase heart rate, blood pressure and respiration rate. Pleasant sounds help create a sense of well-being. Music can be used to treat depression, to reach autistic people and to calm tense patients.
Good acoustic conditions improve patient privacy and promote essential sleep patterns. Such conditions are key to healing. Good acoustic design brings benefits of patient and staff comfort and morale, as well as improved efficiency. It is important to create an acoustic environment that allows rooms to be used for resting, sleeping, treatment, consultation and concentration.
Acoustic design has been a notable part of the design considerations for all healthcare buildings since NHS Estates published its memorandum HTM 2045 in 1996. The need to review the guidance was apparent when the health technical memorandum (HTM) and the health building notes (HBN) series of documents became a critical part of the contractual process, particularly for the Private Finance Initiative (PFI) and similar types of contract.
HTM 2045 contained complex performance requirements and these were often impossible to achieve when other considerations were taken into account. As a result, acoustic design probably got pushed towards the bottom of the agenda. Action was therefore needed to update the guidance.
More pragmatic approach
The Department of Health therefore decided to revise the acoustic guidance and commissioned HTM 08-01. It was published in June 2008 and has now become an established part of the HTM series. It takes a more pragmatic approach than its predecessor, by addressing issues experienced during acoustic design with teams on large and small, new and refurbished healthcare projects, while still aiming to provide good acoustic conditions in healthcare buildings.
The document clearly explains the acoustic criteria and, perhaps more importantly, the implications of decisions that may need to be made if conflicts with other requirements occur. As a result, the advantages of good acoustic performance, the disadvantages of poor acoustic performance, the practical issues and the acoustic targets are more readily understood and accessible by non-specialists. This has lead to a wider adoption of the subject itself, which, in turn, has put acoustics back on the agenda as an important design consideration.
HTM 08-01 gives acoustic guidance and recommends targets for:
- Noise levels in rooms – noise from outside and noise from mechanical services must be at suitable levels. Rain noise is also considered
- External noise levels – noise created by the building and its operation must not affect those around it
- Sound insulation between rooms – private conversations should not be overheard and noisy activities must not interfere with the needs of patients and staff in other rooms. Floor layouts should be designed to avoid people being encouraged to wait or linger outside doors to consulting rooms, for example
- Impact sound insulation – footfall noise from people walking over rooms must not interfere with rooms below
- Room acoustics – acoustically absorbent materials need to be used to provide a comfortable acoustic environment
- Audio systems – audible announcements must be properly heard
- Vibration – must not affect the use of the building, medical equipment and people
- Control of Noise At Work Regulations – designers and estate managers are reminded of their duties under this legislation that protects staff from being exposed to damaging noise levels.
Developing an acoustic strategy
The HTM describes the impact that some acoustic requirements have on other technical and operational needs to aid decisions about design priorities for each project. The keystone of the HTM is that a bespoke acoustic strategy must be developed for each project. The main reason for this is to make sure that informed decisions are made, especially if there are potential conflicts between acoustics and other issues. These decisions need to be based on the user’s acoustic requirements, expectations and operational management policy, and take a balanced approach of the relative priorities for each project.
An important issue for existing buildings is the acoustic performance of temporary and refurbished structures. The HTM advises that if the acoustic targets are appropriate for new healthcare buildings, then they are also appropriate for temporary buildings and those being refurbished. The issues, the people and the acoustic considerations are the same whatever type of accommodation they are housed in.
However, there can be practical reasons why the targets may not be achievable and this is also discussed. For example, if the refurbishment is only to change the internal walls, then noise from outdoors may not meet the targets in HTM 08-01. Again, these issues need to be understood so that informed decisions can be made.
Reducing noise by design
The HTM also advises that a strategy should be drawn up to consider how construction noise and vibration might affect users and buildings in other parts of the estate.
Acoustics should become a consideration right from the beginning of a project, whether it is a new build or a small layout change. Acoustic performance is easily integrated into designs at an early stage but is very difficult to achieve later, so an experienced acoustic consultant should be part of any design team.
For example, consider a site next to a busy road. The design must consider whether openable windows are appropriate for providing the ventilation. Energy and emissions targets mean this is often the preferred solution, but it may lead to acoustic problems. The acoustician should be involved to measure noise levels on site and establish the likely noise levels inside and outside the new building and also to offer advice on the site layout to reduce the impact of noise.
Solutions could include putting rooms that must be mechanically ventilated for clinical reasons on the noisy façades, and making sure appropriate fixed glazing is used. Other rooms where openable windows are clinically appropriate, can then be located at the rear of the building, where noise levels may be lower and allow natural ventilation to be used without compromising the acoustic requirements.
If fundamental issues like this are not identified early enough, significant problems may include:
- Unachievable energy targets
- Unacceptable noise levels in the building
- Project redesign required to relocate departments/rooms
- Extra plant, plant rooms and ceiling void space needed to provide extra ventilation.
Hearing through doors
Another example of the process of making informed decisions is the common conflict between the acoustic performance of doors and the needs of infection control regimes and accessibility strategies. The HTM describes that acoustic privacy through a door is maximised when doors have seals on all edges, including the threshold. However, a seal at the threshold can be undesirable if it introduces a trip hazard, causes a cleaning problem or makes the door difficult to open. In addition, a threshold gap is often used to allow air to flow between spaces, and this means threshold seals are not acceptable.
The HTM also describes how a determined eavesdropper might still hear a private conversation in a room, even if a door has seals on all edges. A door with a high acoustic performance could be used, but this may be too heavy for frail or infirm people to open, leading to the possibility of needing doors that open electrically. The project team must consider all these issues to determine the most appropriate and best value solution while maintaining the acoustic properties.
The HTM also contains useful check lists that non-specialists can use to consider some of the main fundamental issues for their project. Simply reading through these can help inform the client and the designers about how acoustics may influence the project.
The official acoustic yardstick
The British Research Establishment’s Environmental Assessment Method for healthcare (BREEAM Healthcare) is the DoH’s preferred environment assessment procedure for healthcare buildings in the UK. BREEAM Healthcare has adopted the HTM 08-01 targets in its criteria, and up to three credits are available for acoustic performance. This is good reason in itself to promote the HTM’s acoustic performance targets, at a time when projects are demanding higher BREEAM ratings.
The HTM recommends that the acoustic specialist should inspect the construction works. Workmanship is so critical to the acoustic performance of a building that a trained eye is needed to check the installation on a regular basis. Again, if there are issues that are not dealt with during the construction, destructive investigation and remedial works will be needed to fix them. As acoustic tests cannot be done until the construction is complete, remedial works will often delay the finish of the project.
Following the construction of the project, acoustic testing is needed to show whether the targets have been met. The HTM describes a typical testing regime that would normally be sufficient to show whether the targets are met. In the past, there has been confusion about the amount of testing that is appropriate, and the HTM can be used to develop a proposal for testing which all parties can agree on.
In summary, HTM08-01 reinforces the acoustic considerations and allows the subject to be pushed higher up the design agenda. Acousticians should be involved from the early stages to help influence the design of the building. This will achieve a better quality healthcare environment without undue capital cost. The HTM represents an important step forward in delivering high quality, compliant healthcare estate, with the flexibility and pragmatism to incorporate new ideas, healthcare and building technology.