A Tale of Two EWI Failures – EWI Case Studies
Lessons Learned from Two High profile EWI Failures
We have been monitoring outcomes for quite some time on a number of high profile external wall insulation system failures; all of which occurred on high rise blocks in Bootle, Wigan & Glasgow. We have reviewed the Wigan failure and have a clear picture as to why the render system failed at Scholes Village but we cannot yet share this information.
The failure at Stanley House in Bootle has I believe now been rectified but the cause of the failure was never published and we believe that the clients (One Vision Housing) even signed a gagging order as part of the court settlement. You can see evidence of that failure in the next video clip.
Whilst doing continued research on EWI failures we came across commentary relating to the Stanley House failure that has been published by one of the consultants involved in the failure.
After the initial gagging of information it is good to see that a clear picture has now emerged with regard to the cause of this failure; however it has taken years for this information to emerge. The failure mode is unsurprising to us but begs the question as to who was monitoring the quality of this work on site? Missing metal cladding fixings are a very easy thing to spot and correct, even to the least discerning eye. There was an immediate and urgent need to install a mild steel mesh around 6 buildings but we are unsure if this was installed as a temporary or permanent measure. There are some forms of insulation such as phenolic, that once wet need to be removed from the building. It will be interesting as we move forward to see if there are attempts to reinstate or repair failed and saturated EWI systems. Some systems such as those containing XPS insulation will present greater flexibility for repair and re-instatement than others.
We next come to a case that has always been incredibly difficult to uncover information about… GHA’s Mini-Multi blocks. These blocks experienced failure very early after completion in 2010 and we saw reports of ‘extensive blistering’ in a number of blocks. The main contractor, ROK, went bust but they were not the EWI installer and we are unsure who ultimately footed the bill for remedial works.
The consultant dealing with this also published some recent findings with regard to these failures and we believe that remedial works are now complete; however we have to say that we find their reported reasons for failure as a little unusual. The consultant stated that ‘The render on GHA high rise blocks had started to blister. The failure was identified as being due to a lack of water permeability in the topcoat.’ This directly contradicts information given to GHA residents by GHA representative, Ian Duff, who stated that ‘moisture and evaporation got in behind the over cladding.’ We are unsure if it ‘got in’ through failed building joints or whether wet insulation was installed but for either eventuality, no amount of permeability in the topcoat was going to lose this moisture through an evaporative process.
The idea that these systems absorb moisture by the ‘overcoat’ principle is simply wrong and if they take in water through failed building joints or if wet insulation has been installed due to poor site storage facilities then the render coat is not designed to lose this moisture by permeability or breathability. These are weatherproof systems and water ingress will usually write off the affected underlying insulation. We always believed that such premature failure and blistering was a sign that the insulation was wet when installed but we are now even seeing systems installed with no sealant at all around windows and other critical junction details and these critical omissions would also be responsible for such rapid system failure.
There are two critical lessons to be learned from both these failures:
- Clients must have a robust and independent system in place for the quality management of works.
- Clients must understand their specification & the terms of their BBA approval to ensure that there is no diversion from the agreed specification.
An interesting discussion developed after this blog was posted with regard to the GHA EWI failures. Two separate interested parties told me that occupancy issues were believed to be a factor in these failures. The logic behind this is that the flats had a high number of ‘stay at home’ occupants, possibly retired or unemployed. Therefore flats experienced a higher than average level of relative humidity, which permeated through the walls into the EWI system insulation. This is an interesting theory but given the rapid system failure it is not one that I think holds a great deal of validity. Moreover, if occupancy issues are a significant risk factor for EWI failure then you would need to complete a condensation risk assessment for every project during the design process. (This does not mean a risk assessment for interstitial condensation, which is something I’d expect to see done on every project anyway)
In theory, it is a reasonable proposition and of course we know that EWI should not be installed on wet walls because evaporative moisture can and does cause significant problems. However, there is no need to hypothesise about this potential factor since internal data logging can easily monitor and record internal environmental conditions, thereby providing a complete picture with to regard occupancy issues. Secondly, hygroscopic moisture content (HMC) and capillary moisture content (CMC) can also be checked and recorded in the building fabric to check if internal relative humidity is in fact having a significant impact on total moisture content within the building fabric. If the building fabric is dry then occupancy issues are not a significant factor.