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Indoor air quality - the elephant in the low carbon room?November 2013

"As a knowledgeable sector we must not become rabbits in the zero carbon headlights - there are other issues that need attention too!" Richard John, BSRIA

The science of climate change is now well accepted, and as such the UK’s international leadership, albeit faltering, in moving towards a low carbon economy must be welcomed. As always there are unintended consequences. So when we decarbonise and clean up our power stations, Ofgem predicts an increased likelihood of power failures (Ofgem, 2013) because of the associated reduction in generating capacity available at peak times. It is also an oddity of government policy that, just as we are experiencing a decrease in generating capacity, there is a marked enthusiasm for supporting the increased use of electrically-driven heat pumps. Certainly if they displace direct resistance heating this should be a benefit but as an alternative to gas fired heating they will exacerbate the issue.

Of course one solution to the surplus problem is to simply reduce demand and there are many government actions in place to make this happen. Policies to improve insulation and reduce ventilation leakage through Building Regulations, ECO, and Green Deal all aim to reduce demand.

However when it comes to a tightening of standards associated with new and existing buildings there are some signs that the unintended consequence is the impact that such standards have in practice on indoor air quality and hence the functionality of buildings. There is an old adage “build tight, ventilate right”. We are certainly learning to do the former but BSRIA’s experience is that we haven’t got the latter bit sorted.

Indoor air quality (IAQ) is a complex issue. In housing, a reflection of poor IAQ can be an increase in mould and damp problems associated with poor ventilation, and associated health effects. In schools it can be sleepy pupils. At another level, IAQ is more subjective. Certainly we recognise the bracing nature of seaside air with its tang of salt and ozone but some also recall the comforting fug of a pub complete with its smells of beer, tobacco and wood smoke. So IAQ is subjective, has time-based attributes, and a very large number of possible measured variables to consider.

Many practitioners use a measure of carbon dioxide (CO2) concentration in a building as a proxy for IAQ. Various national bodies such as the Department for Education have set standards for CO2 levels in buildings in its own right – in this case stipulating a maximum average value of CO2 of 1500ppm (DfE 2012). In the UK the current Part F of the Building Regulations implies that indoor air concentrations of CO2 should not exceed ~1200ppm. Others argue about the need to look at concentrations of a wide range of indoor pollutants, rather than a single proxy value. Finally, quantification of the disbenefits of poor IAQ in terms of, for example, health effects, remains an inexact science, albeit an improving one.

So what’s the link between IAQ and the quest for lower carbon buildings, in part driven through ever tighter regulations? Surely ventilation needs are fully addressed by Part F of the Building Regulations? Well let’s start with the difference between design intent, actual use, and the law of unintended consequences. In the housing sector there is increasing evidence that we are getting better when it comes to making buildings tighter. In BSRIA’s experience of monitoring such buildings, airtightness is improving in part through progressive airtightness testing requirements but there are often significant failures to operate mechanical and even passive ventilation systems to ensure that occupants have sufficient fresh air.

There are multiple practical issues which conspire to affect the effectiveness of ventilation. Actual occupancy rates don’t always equate to design conditions. Flow rates associated with mechanical and passive ventilation systems in practice don’t always equate to design. There are many reasons for this including:

  • Design. Impractical designs and / or designers “gaming” with calculations so as to demonstrate that standards are met.
  • Construction / Installation. Ductwork can be prone to damage (particularly, flexible systems), and the practical installation of ductwork, fans, and terminal units does not always equate to what was designed. BSRIA has come across instances of mechanical ventilation systems simply not being connected up to a power supply. Some buildings have a lower air leakage rate than the design.
  • Commissioning. Poor commissioning, such as ventilation dampers, sensors and controls, can significantly affect performance. The current approved method of measuring air flow from low pressure ventilation systems is also fundamentally flawed, so in practice we don’t really know what the true situation is in many buildings even when these systems are ‘properly’ commissioned.
  • Maintenance. Poor maintenance of filters and sensors can have a significant impact on flow rates and the effectiveness of filtration. Design issues sometimes make the cleaning of filters or their replacement, or the cleaning of ductwork, somewhat problematic.
  • Operation. Occupant effects such as not using the ventilation system as per the design intent; manual tampering of controls, sensors, dampers etc. Where mechanical ventilation works with trickle ventilators, they may be taped shut.

Wider experiences in housing can be found in a report from the Zero Carbon Hub (ZCH 2013), and BSRIA looks forward to the forthcoming publication of an assessment of mechanical ventilation systems supported by the Technology Strategy Board through its Building Performance Evaluation programme, in which BSRIA has been closely involved.

In social housing with mechanical ventilation systems, BSRIA has noted CO2 levels of greater than 2000ppm during occupancy in more than 20% of buildings studied for Housing Association clients. This is a strong indication that many mechanical ventilation systems are not functioning, or not being allowed to function, in line with expectations.

BSRIA’s experience suggests that one of the key factors as to whether mechanical ventilation systems work is how well mechanical services and their implementation are understood by the client and their supply chain. At one end of the spectrum are clients who have expertise in-house to ensure appropriate design, installation, commissioning and operation of mechanical ventilation systems, the selection and management of their supply chain.

At the same time these clients recognise that systems need to be selected to reflect occupants’ needs and the abilities of their facilities teams. They also recognise the importance of handover to the occupants and go to some lengths to ensure that this is done – and that expertise is not just available at handover, but is ongoing. Such clients have also learnt that the maintenance of mechanical ventilation systems requires an appropriate level of competence and resource for these systems to perform well in the long run.

Recognising that good practice examples exist, perhaps one of the key requirements for this particular sector is the establishment of a “best practice” supporting infrastructure which provides industry recognised guidance, advice, and training. BSRIA has an important role here.

More broadly, low carbon standards are driving innovation across the UK, but one of the unintended consequences of a supply chain not fully trained and proficient in accommodating such innovations is that we can end up designing sometimes complex systems which don’t come close to meeting design intentions in terms of either energy or IAQ.

It was one of the conclusions of the recent Department of Business Innovation and Skills (BIS) report into low carbon construction (BIS, 2010) that to meet carbon emissions reduction targets means a steep learning curve for the construction and property supply chains. If requirements associated with IAQ are added there is yet more to learn.

IAQ is not an exact science, but some recent work from the Lawrence Berkeley National Laboratory (LBL, 2012) in the States provides an indication that CO2 emissions in their own right have a significant impact on cognitive ability. The results imply that levels of CO2 found in a significant proportion of well-sealed mechanically-ventilated homes and other building types can have an impact on certain cognitive functions.

The zero carbon goal for 2019 will be very difficult to achieve on its own. As a knowledgeable sector we must not become rabbits in the zero carbon headlights - there are other issues that need attention too!

Richard John is Director of Sustainable Construction at BSRIA.

BSRIA provides a range of compliance services for Building Regulations including airtightness, ventilation and sound insulation. For more information phone BSRIA on 0800 5871000 or email

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