Does Natural Ventilation Work? – References and Links

I’ve had a couple of requests for links to the sources for “Natural Ventilation – does it work?”, my article for Passive House Plus Issue 6 (start of 2014), so here is a list of most of them – live as at the time of posting in April 2014, but no guarantees they will remain so of course.

My apologies where (a few) refrences are behind a paywall – it usually means either that I’ve wriggled my way behind it somehow (though if your subscriber-only publication is on here, not yours, obviously 😉 ) – or a helpful academic has supplied me with a copy. Or alternatively, it means that I’ve only referred to the abstract.

The references are roughly in order of their appearance in the article. Here you go:

The NHBC Foundation’s commendably honest account highlighting a string of concerns in the design, specification, installation,  commissioning and operation of MVHR systems in 10 ‘zero carbon’ homes: Assessment of MVHR systems and air quality in zero carbon homes NHBC Foundation August 2013 (Greenwatt Way study) (NB you have to register to download this, but registration is free)

Neil Jefferson, director of the NHBC writing in Building magazine, questioning whether MEV, PSV or natural ventilation are exempt from the performance issues that NHBC uncovered with (non-Passivhaus) MVHR installations in the study above:

Bob Lowe’s 2000 modelling study investigating the “under-ventilation index” for naturally ventilated dwellings (the proportion of the heating season for which a dwelling will be underventilated without additional window opening). His results suggested that even for leaky buildings that lose heat unnecessarily in very cold or windy weather, and are generally over-ventilated (draughty!),  under-ventilation for a proportion of the time (in mild and/or still weather)  “is almost assured”: Building Services, Engineering, Research & Technology 21 (3) 179-186 R. J. Lowe: Ventilation Strategy, Energy Use and CO2 Emissions in Dwellings – a Theoretical Approach (abstract)

Simon McKay & David Ross (AECOM), and Ian Mawditt & Stuart Kirk (Building Services Ltd) carried out a small study (of 22 homes of different types)  for DCLG, to investigate whether Part F 2006 was providing adequate ventilation and IAQ in homes, and whether it should be uprated at the review in 2010. They found that all of the flats and 40% of the houses failed to achieve the recommended background ventilation rate; NO2 and volatile organic compound levels exceeded guidelines in a number of dwellings – and this was with all vents open and fans running. When the researchers arrived however they had found 60% of vents were closed and many extract fans disabled. Six of the 22 households didn’t use their kitchen and bathroom extract fans at all, and five said they used the isolator to control some of their fans  – though in fact many more actually did so: Ventilation and Indoor Air Quality in Part F 2006 Homes BD 2702 DCLG 2010, and  Ian Mawditt’s  presentation on the findings, showing the position of vents and fans as normally used by occupants

Stirling Howieson of the University of Strathclyde has reported on the basis of his recent research that “technical standards prescribed by the Building Regulations are not being enforced”. He also found that natural ventilation tends not to be used as intended and fails to give good IAQ. Howieson and colleagues looked at 24 new-build homes constructed to  2010 regulations, where trickle vents in the windows provided the only source of background ventilation.  CO2 levels measured in occupied bedrooms “were found to be at unacceptable concentrations” (occupied mean peak of 2317 ppm with a maximum of 4800 ppm): “Are our homes making us ill?”, Stirling Howieson, University of Strathclyde. Perspectives in Public Health 2014 in press, abstract at

Derrick Crump, Sani Dimitroulopoulou and colleagues at BRE carried out a study of ventilation and indoor air quality in 37 homes in 2002;  although the sample were approximately as leaky as the average stock,  the majority (68%) of the sample had below the recommended design air change rate of 0.5 ach. And some suffered indoor air pollution issues: in winter 18% of the homes during winter had kitchen CO levels above WHO guidelines, and even in summer, 13% of them did.  In winter the kitchens of six homes also exceeded NO2 guideline values: VENTILATION AND INDOOR AIR QUALITY IN NEW HOMES Crump, Dimitroulopoulou et al BRE, Watford, The study is also summarised here

A Good Homes Alliance report presenting examples of good ventilation practice in low energy homes highlights only a few projects with natural ventilation (three with vents plus humidistat-controlled extract, two with passive heat recovery, and one with a passive stack system). Even so, two of the six dwellings had had poor IAQ , which was attributed to occupant behaviour: in both cases, occupants said they had closed vents/shut off fans because of noise or draughts. IAQ was poor in both cases.  (Air quality in the other four of the six naturally ventilated dwellings was good):

Contrary to general expectation, buildings may become more airtight as they age – which may also present an issue for ventilation design recommendations. In one NHBC study,  eight of 23 homes became more airtight 1-3 years after completion. And in the NHBC’s Greenwatt Way study (see link above), 9 out of 10 homes became more airtight.

Some research suggests that in order to reduce the risk of house dust mite problems (mites are known to exacerbate asthma in particular) relative humidity below 60, or even lower, should be sought: Lawrence Berkeley National Laboratory,


Passive House goes large

Passivhaus is no longer just the preserve of the self-builder: more and more large Passivhaus schemes are being announced. These include both non-domestic buildings, for example in schools and universities,  and multi-housing schemes, generally in the social rented sector, though sometimes with a portion for private sale.

In this article for Passive House Plus magazine I looked at some of the economies of scale available on larger Passivhaus projects, and some of the obstacles that larger schemes may run into. Also, following from my previous article on the cost of Passivhaus, I looked a bit further into the economics of Passivhaus from the point of view of developers and owners – in both the domestic and the non-domestic sectors.

Read the article in pdf here: Passive House goes large

My thanks to Passive House Plus for the use of this document.

The cost of building passive

Passivhaus (Passive House) is often thought of as being “too expensive” for the mainstream. There are some designers and developers however who are managing to shave the capital cost premium down to just a few per cent – or even zero.

In researching this article for Passive House Plus I learned that the extra costs, where they are incurred, seem to derive from two main sources:

  • Passivhaus components tend to be more expensive than the “conventional” alternatives – though this difference is diminishing all the time; and
  • There is a “learning curve” in first (and probably second and third) Passivhauses for any team, where designers and contractors alike need to spend a bit longer working out how to co-ordinate their activities to ensure that details are buildable, and that built quality matches up to the standards sought.

The extra costs are mainly up-front; looked at over the building’s first decades of lifetime, running cost savings – including maintenance, and even cost associated with tenant dissatisfaction – start to pay back the initial investment.

Of course a key question is “costs compared to what?” – and as statutory building standards edge upwards, you might expect the “standard” and Passivhaus build costs to converge – thus, for example, mechanical ventilation is increasingly commonly installed in non-Passivhaus dwellings, simply because Part L of the building regulations is looking for more energy efficiency and hence higher airtightness.

However, a couple of caveats:

  • Mainstream dwellings built even to high notional standards may employ cheaper construction “models” with less quality control, and therefore, leave bigger performance gaps; and
  • Passivhaus is offering more than just energy savings, it is also concerned with comfort and occupant health – something that has clear value, but is perhaps hard to price in the context of a shortish article.

I was particularly interested in the perspective from some of the people I spoke to, suggesting that insulation (literally!) of occupants from rising and unpredictable energy costs was not only attractive to owner-occupiers, it was also attractive to landlords and to lenders, as problems with soaring energy bills appear to be playing an increasing part in rent and mortgage arrears – making a Passivhaus building a better bet for investment.

Several people suggested to me that if building standards (and testing standards) were set higher, “levelling the playing field”, this would reduce the competitive advantage of low-efficiency, shoddy building – and with it, reduce the cold wind that whistles though the performance gap and straight into occupants’ wallets.

Unfortunately, to bring about this kind of improvement, I can’t help feeling big developers would have to devote less energy to lobbying for the status quo, and more to changing their modus operandi. But with the first record of a Passivhaus building (in Frankfurt) offering heat “too cheap to meter”, customers may yet demand the same here.

Read the article in pdf here: The cost of building passive

My thanks to Passive House Plus for the use of this document.