Tuesday, 6 January 2015

Do energy efficient homes damage your health?

I recently read two conflicting news stories:

Warmer homes mean fewer GP visits for lung patients
Study finds energy saving home retrofits could increase asthma risk

In the first, fitting insulation and new boilers in patients homes improved the health of patients with chronic obstructive pulmonary disease (COPD) in Sunderland. In the other, a survey of residents in social housing in Cornwall found that those living in homes with high SAP ratings – so more energy efficient – had higher rates of asthma than those in much worse housing. What does this mean? Are energy efficient houses good for you or not?

One thing to note is that the COPD study was very small – only 6 patients whereas the Cornwall study included about 700 cases. That lends weight to the Cornwall study.

Another point is that in the Cornwall study the homes were divided into four equal sized energy efficiency categories by their rating (1-120) but there wasn’t really that much difference between them. The middle two categories were rating 60-71 so they would be classed as C or D. The top group would be classed C or above and the bottom group covered homes in D, E and F. Nationally, the average is D and when the regulations start in 2018 all rented property needs to be E or better. So although most of these properties would be regarded as not that bad the best of them were not much above average.

I think it is generally accepted that living in cold, damp homes is bad for you. In the Sunderland study they measured room temperatures before and after the retrofit and found up to 42% increase in living room temperature. I presume that means on the centigrade scale – so if it was 14C before it might be 20C afterwards. I can well imagine that would be beneficial for health.

Unfortunately there was no temperature data in the Cornwall study. It was based mainly on data from questionnaires, not measurements, and the SAP for the homes were provided by the social housing provider. SAP is only an approximation even when calculated by the most expert surveyors.

I don’t wish to cast aspersions on the social housing provider but I think it is a bit worrying that 20% of homes even in the top SAP group ‘had a musty odour in the last 12 months’ and 35% had ‘visible mould contamination in any room’. However they were much better in this respect than the other groups. In fact the worst group for mould was in the middle for SAP rating – 66% of homes in that group had visible mould. Maybe this is something to do with living in Cornwall. You do get a lot of wet in the South West.
From the Cornwall study: the most efficient homes (SAP >= 71) had least mould but residents were most likely to have asthma.

Mould can occur even in high quality homes if ventilation is not sufficient, especially if the occupants are careless about it. Closing up trickle vents, drying clothes on radiators, not turning on extractors in kitchen and bathroom are all excellent ways to grow mould. Mould grows faster in warmer homes, and mould does exacerbate health problems especially to do with lungs. My friend with COPD and asthma is much improved after moving into a new flat even though he complains it isn’t as warm. The old place was over heated and under ventilated. It wasn’t a great surprise that they found mould behind furniture and under carpets when they cleared it out (probably related to a plumbing leak some years before).

Another very interesting point was that in the top SAP category asthma was strongly associated with mould but in the bottom category mould did not seem to be significant. There are at least two possible interpretations of this:

  1. In the bottom category there was so much mould it was always a factor
  2. Mould isn’t too serious unless there is also a lack of ventilation as well, and the top category of homes were more air tight and needed better ventilation. 

I suspect that in practice both of these are true. Mould would have been almost ubiquitous in the poorer housing but the presence of mould is much more serious when there is poor ventilation as well. There is good general advice on this on ventilation strategies from Transition Cambridge here.

I wonder, too, if the allocation of residents to homes was not entirely random. It is quite likely that a social housing provider would try to put residents with health problems into the best homes they could find. So, it may be that some of the prevalence of asthma in the best homes was because those people had asthma before.

Anyway – are there any lessons we can learn from this? I think we can safely say:

  • Mould is bad for health especially where ventilation is poor.
  • Getting the ventilation right is very important in more energy efficient homes with good air tightness.


  1. I am not sure your analysis is completely correct. The occurrence of mould is closely linked to high RH levels, itself related to the amount of moisture in the air. High moisture levels are indicative of poor ventilation but this can occur at high or low temperatures. In fact its worse at low temps. Its actually quite hard to get mould growing in warm homes: it's usually a symptom of the homes not being warm all the time, or there being some cold patches to be found.

    1. You mean that the mould growth in energy efficient homes is probably related to cold patches rather than humidity? This is also possible, but it doesn't explain why the asthma levels we higher in the energy efficient homes even though mould levels went done. There must be another sensitising factor - perhaps poor ventilation or a pre-existing condition or something else. We don't know if these homes were properly heated. The worst possible scenario would be under heated and under ventilated!

  2. Gah, lost thist first time so here goes again...

    I think mould is a partial red herring here. I'm not a medic but understand that asthma can be directly exacerbated by high RH (underventing) as well as low RH (overventing with some of the oversized MVHR unit's i know of). Also, high RH encouraged dustmites. Mould is bad, and importatn but perhaps not central here.

    How well has the study controlled for, e.g. prioritisation of asthmatics for efficient homes, if this is a practice (I speculate...)

    It's not efficient homes that exacerbate asthma, it's badly designed/built and "badly operated" ones - but occupants not necessarily responsible for the latter!

  3. There has been a lot of discussion on twitter about this study, so I thought I should mention some of the issues raised. I have assumed that the high SAP scoring homes were more airtight - but SAP does not measure air tightness or air quality at all. Air tightness is usually improved significantly when homes are externally insulated or when double glazing is fitted. But we don't know what state the top SAP group of homes were in.

    SAP is based on cost of heating, and homes with gas heating score better in this respect. 85% of the top SAP group were on mains gas but only 18% of the bottom SAP group. So gas heating could be a contributing factor. But there was no significant difference in asthma between the on-gas and off-gas homes within any SAP group which suggests this is a red herring. I sincerely hope so because there are awful lot of people using gas in the country including me!

    There isn't enough information in this survey to answer the questions properly but there is enough to raise concern, in my view.

  4. It's also possible that "energy efficient" doesn't equate to "warm." We tend to assume that a well insulated house is going to be warm, but the way people choose to live in their homes is subject to huge variations and just because a house is easier and cheaper to keep warm, it doesn't follow that it will be run that way. An airtight, cold house would be the worst outcome for mould, air quality and asthma.