TheTrap: Cavity Wall insulation with no attention to ventilation
Cavity Wall insulation is associated with increased indoor humidity which is a risk factor for condensation and mould. Home owners suffering from black mould are told by installers and CIGA inspectors that humidity and condensation is the cause of their damp, yet home owners are also told that 'disturbing the insulation' which includes installing through wall vents apparently invalidates the 25 CIGA guarantee. The industry need to stop blaming home owners and guarantees should be fit for purpose.
Occupiers instinctively know that living in a dwelling with visible mould has health implications.
With the recent publication of the PAS2035 standards for retrofit ventilation has been promoted to a 1st class citizen which must be addressed in any retrofit.
Ventilation is incredibly important for the management of humidity, controlling mould growth and expelling various particulates from the room. The sort of particulates that are thought to be detrimental include anything from airborne mould spores to volatile organic compounds that slowly release from modern paints, sealers and furniture.
As an aside; Indoor air quality is about to receive more prominence as NICE publishes its guidance in Dec 2019.
Cavity wall insulation was installed en masse under government sponsored schemes without any consideration for ventilation, humidity and indoor health. The emergence of condensation and mould after the installation of CWI is blamed by the industry and even some surveyors on 'occupation' though many homeowners cannot point to any material change in their habits or behaviours since the installation of retrofit.
In fact it's easy to argue that it's a basic human right to dry clothes indoors in winter and that houses should be fit for purpose. If this activity suddenly started to cause problems with condensation following a retrofit solution then it could be argued that the solution was not fit for purpose or not sensitive to the usage pattern of the house.
Old houses are leaky. The gaps around windows and floor joists leaks humid air from the room through the cavity which in a normal ventilated cavity allows it to escape to outside.
Air flows move moisture around the fabric of a building much more readily than diffusion though a wall e.g gypsum plaster.(The Build show has an accessible explanation of diffusion vs leaks).
Sealing the cavity cuts off this path of ventilation which may lead to a increase in indoor relative humidity which will condense on the colder surfaces, especially areas of cold bridging.
This is quite intuitive but there is also some formal evidence to back this. A study[1] of impact of 'energy upgrades' over 2 winters homes in Wales give us some idea of the actual increase in humidity from various energy saving measures.
The numbers are not big, but crucially the data points come from real houses with occupation and is calibrated by controls which had no upgrades in energy measures.
Here is a table of % increase in relative humidity of different interventions.
It makes complete sense that installing new windows sealed with expanding foam increases relative humidity which is why trickle vents on windows have been part of the glazing standards for some time.
Cavity wall insulation was close behind windows and associated with 4.57% relative increase (which e.g. would mean a home at a relative humidity of 60% could increase to 62% post CWI). Although modest, it's entirely possible that an increase pushes a house into decompensation in the winter months leading to visible mould in the face of normal occupancy patterns and activities.
The industry focus on the notion that the inner skin of external walls should be warmer post CWI due to presence of insulation, leading to less surface condensation. This is good in theory, but the number of cold bridges in the form of lintels or solid cavity closers means that cold spots will be just as cold and a an increase in Relative humidity caused CWI will exacerbate problems. We also know that voids and poor filling around windows is pretty much the norm for products such as mineral wool and I'm not aware of any real world testing over e.g 2 winters (as with the Poortinga study) that backs up the industry's views.
All this is moot as for example the CIGA 25 year guarantee has a clause invalidating the guarantee if the insulation is 'disturbed' which would include through wall vents.
Not-to-my-home is aware of installers rejecting claims for poor workmanship based on some benign modification done somewhere distant from the problem - e.g modificaiton of catflap in an unrelated part of the house.
Not-to-my-home is aware of RICS surveyors who have suggested that lack of ventilation is the cause of mould in the house but denied that CWI would increase or even cause the problem, even when there was evidence of voids and cold bridges in the cavity.
Increases in indoor relative humidity levels were only found for buildings that received cavity-wall insulation (which generally was installed without mechanical ventilation).
CIGA, installers and the industry must stop blaming problems on owners especially when these mass installations were rolled out without adequate testing on our varied and ideosynchratic housing stock.
The guarantee is not fit for purpose.
[1] Poortinga W, Jiang S, Grey C, Tweed C. Impacts of energy-efficiency investments on internal conditions in low-income households. Build Res Inf 2017;0:1–15. doi: https://doi.org/10.1080/09613218.2017.1314641.
[2] Poortinga W, Jones N Lannon S, Jenkins H, Social and health outcomes following upgrades to a national housing standard: a multilevel analysis of a five-wave repeated cross-sectional survey BMC Public Health. 2017; 17: 927. Published online 2017 Dec 2. doi: 10.1186/s12889-017-4928-x
Occupiers instinctively know that living in a dwelling with visible mould has health implications.
Ventilation is incredibly important for the management of humidity, controlling mould growth and expelling various particulates from the room. The sort of particulates that are thought to be detrimental include anything from airborne mould spores to volatile organic compounds that slowly release from modern paints, sealers and furniture.
As an aside; Indoor air quality is about to receive more prominence as NICE publishes its guidance in Dec 2019.
In fact it's easy to argue that it's a basic human right to dry clothes indoors in winter and that houses should be fit for purpose. If this activity suddenly started to cause problems with condensation following a retrofit solution then it could be argued that the solution was not fit for purpose or not sensitive to the usage pattern of the house.
Does CWI increase indoor humidity?
For most houses. Yes.
Air flows move moisture around the fabric of a building much more readily than diffusion though a wall e.g gypsum plaster.(The Build show has an accessible explanation of diffusion vs leaks).
Sealing the cavity cuts off this path of ventilation which may lead to a increase in indoor relative humidity which will condense on the colder surfaces, especially areas of cold bridging.
This is quite intuitive but there is also some formal evidence to back this. A study[1] of impact of 'energy upgrades' over 2 winters homes in Wales give us some idea of the actual increase in humidity from various energy saving measures.
The numbers are not big, but crucially the data points come from real houses with occupation and is calibrated by controls which had no upgrades in energy measures.
Here is a table of % increase in relative humidity of different interventions.
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" Increases in indoor relative humidity levels were only found for buildings that received cavity-wall insulation (which generally was installed without mechanical ventilation), not in British steel-framed buildings or in buildings with solid walls receiving external wall insulation (which was accompanied by extractor fans)." - Poortinga et al
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Cavity wall insulation was close behind windows and associated with 4.57% relative increase (which e.g. would mean a home at a relative humidity of 60% could increase to 62% post CWI). Although modest, it's entirely possible that an increase pushes a house into decompensation in the winter months leading to visible mould in the face of normal occupancy patterns and activities.
The industry focus on the notion that the inner skin of external walls should be warmer post CWI due to presence of insulation, leading to less surface condensation. This is good in theory, but the number of cold bridges in the form of lintels or solid cavity closers means that cold spots will be just as cold and a an increase in Relative humidity caused CWI will exacerbate problems. We also know that voids and poor filling around windows is pretty much the norm for products such as mineral wool and I'm not aware of any real world testing over e.g 2 winters (as with the Poortinga study) that backs up the industry's views.
The big catch
Faced with worsening humidity post CWI the installation of extractor fans is a relatively simple solution but by their nature they are expelling warm air out of the house that the occupants have spent money heating and so start to erode the benefits of a energy saving retrofit. While there are technologies such as single room heat recovery units, the ideal would be a whole house ventilation and heat recovery systems which for many homes will be disruptive to install and prohibitively expensive (especially when compared to the 'free' CWI).
All this is moot as for example the CIGA 25 year guarantee has a clause invalidating the guarantee if the insulation is 'disturbed' which would include through wall vents.
Not-to-my-home is aware of installers rejecting claims for poor workmanship based on some benign modification done somewhere distant from the problem - e.g modificaiton of catflap in an unrelated part of the house.
Not-to-my-home is aware of RICS surveyors who have suggested that lack of ventilation is the cause of mould in the house but denied that CWI would increase or even cause the problem, even when there was evidence of voids and cold bridges in the cavity.
Potential harms
As part of their wider programme of study. Poortinga at all in a followup study[2] looked at the Social and health outcomes following energy saving upgrades to housing stocks and singled out Cavity wall insulation as the only intervention associated with poorer health and mental health outcomes.
Certainly CWI does not seem to be the sort of intervention that the fuel poor should be offered in isolation as it's associated with much poorer health which we are told it was meant to solve.
Increases in indoor relative humidity levels were only found for buildings that received cavity-wall insulation (which generally was installed without mechanical ventilation).
CIGA, installers and the industry must stop blaming problems on owners especially when these mass installations were rolled out without adequate testing on our varied and ideosynchratic housing stock.
The guarantee is not fit for purpose.
[1] Poortinga W, Jiang S, Grey C, Tweed C. Impacts of energy-efficiency investments on internal conditions in low-income households. Build Res Inf 2017;0:1–15. doi: https://doi.org/10.1080/09613218.2017.1314641.
[2] Poortinga W, Jones N Lannon S, Jenkins H, Social and health outcomes following upgrades to a national housing standard: a multilevel analysis of a five-wave repeated cross-sectional survey BMC Public Health. 2017; 17: 927. Published online 2017 Dec 2. doi: 10.1186/s12889-017-4928-x
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