The controversy over Cavity Wall Insulation 'topups'

In this article I talk about the practice and problems of topping up insulation when voids are discovered, why it is being done and the potential violations of building regulations.
I can only put forwards what I have understood from public documents and personal correspondence  So I welcome corrections or clarifications from the industry on this important issue for home owners and will happily update this post to reflect any inaccurate statements.

We know that 100s of topups are done every year.  From what I can gather : If the BBA have not approved these topups then the relevant local authority building control should have been notified prior to topping up as an 'off licence' use of the product.  It is not clear that the correct procedures are being followed in all cases.

Background :Voids are common

A void is simply an area cavity between the walls which is missing insulation.  If a void is large enough then the insulation will not be compliant with the meter square target density set by the BBA for a particular product which would be considered a defect in materials and/or workmanship as covered by the 25 year CIGA guarantee.

Achieving a uniform full fill insulation without voids in Cavity wall insulation is a difficult task even when the manufacturer's drill patterns are strictly adhered and when the cavity is clear (old cavities are never clear).

Getting the correct uniform density is impossible for blown mineral wool as proved by the BBA under lab conditions. There were no voids in the their tests but they have suggested that areas of overly dense insulation surrounded by more sparse insulation can also cause problems of water penetration.

Importantly a single 2 hours visit, CIGA's guide to how roughly how long it takes to install, is unlikely to produce sufficient density of fill for certain insulation types. Even if the fill looks good on the day, research  shows that weeks after the installation there can be signs of settlement and voids sometimes called 'dry slump'.

A paper on Cavity Wall insulation in Germany makes it clear that for adequate quality control, followup themographic study is advised to identify voids in and refill with 40% of properties showings signs of needing top ups to meet the standards.

Cavity Wall Insulation in existing buildings. Wigger et al

Joe Malone at Building defects analysis has a good article about failure mode of mineral wool and also echos this thought :

"Realistically, all properties would be best having a follow up visit to top up the fibre CWI after it has slumped but this rarely, if ever occurs." - Joe Malone, Building defects  analysis web site.

Several large thermography studies have shown a large number of voids and  a large study of the Northern Ireland housing exective' housing stock conducted by BBA CIT showed that 

• 63% of the Social housing dwellings surveyed were non-compliant with industry standards and the BBA certificate.
• 36% of private dwellings were non-compliant.

Part of this non-compliance was due the presence of voids. But only 3 dill holes were made to check for voids and these were not guided by thermography therefore are likely to underestimate the prevalence. 

NIHE Cavity Wall Insulation Research Project 2019, BBA CIT

All this suggests  that the installation guidance from BBA and CIGA based on drill hole patterns alone were (and may still be ) inedequate on their own to guarantee a uniform  fill.  Certainly for mineral wool insulation.

On the surface there seems to be a very good case for a post install (independent) survey several months after install to verify the performance and check for any settlement.

The problem with repeat visits and followup thermography + refill of voids is that it starts to erode the notion that CWI is a cheap and easy upgrade to a home's insulation. As the cost increases, the payback time increases and home owners may be less likely to sign up.

Thermography is not a simple exercise because it can only be done effectively in the colder months where there is a suitable heat gradient between indoor and outdoor. It cannot be done on a sunny day.
And of course there is the extra cost and invonvenience for the home owner of a follow up check on the insulation.
However, one could argue that the investement put in early on to arrange a post install survey and thermography a few months later would have saved an awful lot of tears and litigation 10 years down the road.

After market top ups and building regulations

So for certain types of insulation, there is a very high likelyhood of voids. Some voids may be associated with damp problems but some may only be found when e.g windows are changed in a house or a damp problem is investigated and the cavity wall insulation is scrutinised. Some may be highly suspected from thermographic studies and confirmed by inserting a boroscope into the cavity.

Imagine 10 years down the line after CWI was installed, the home owner discovers 1 meter square area of the wall is found to contain no insulation.  CIGA investigate and instruct either the original installer (or a remediation contractor if the installer is no longer trading) to top up the insulation. Simple.

Although it seems logical to simply top up with the original insulation, the BBA certificates for existing product in the market do not have any statement about what to do in this situation in the same way as my the BBA certificate for my insulation doesn't specify how to remove if it is found to be a faulty install.

BBA approve complete CWI systems

If the original BBA certificate does not mention topping up as an approved use case then using a BBA product 'off licence' requires specific building regulations approval.

BBA have made this very clear in a letter in the LABC website from 2012 entitled:

"Re: BBA position statement with regard to installing cavity wall insulation outside the scope of BBA approval with particular reference to partially filled cavities"

Here they say that any company installing a BBA product in a use case not covered by the original certificate must go though the local authority building control and do so with at least 48 hours notice.

Are topups being done without proper building control approval?

I am aware of one case where a topup was proposed without BBA or building control approval. I have no idea if this is a wider problem as there is little public discourse on the issue.

We know that 100s of topups are done every year. CIGA for instance publish statstics in their annual reports. And claim to have authorised 247 'reinjections'.

What worries me is that if the act of topping up invalidates the BBA approval it could  means that further problems with the insulation in the future may not be investigated by either the BBA or the system designer.

 I won't dwell on the tecnical side too much, but here are just two  issues which might make topups difficult:

1. If the original system designer is no longer trading then there is no equivalent material to top up. Mixing different BBA approved products in the same wall sounds like an awful idea. Aside from the different physical properties and manufacture. Which system designer will take the liability and complaint against their product in future if it was mixed with some defunct system?
2. A void may be a surrogate marker for other problems such a lackof a adequate pre installation survey or other fundamental defects in workmanship. (see photo below showing that the void is caused by bridging mortar interrupting the fill and so the solution is not simply to re-inject and really the whole state of the insulation needs to be assessed).
   Where there is smoke, there is fire as the saying goes.

My view is that topups as part of a quality control procedure around the time of install could  be a sensible step in quality improvement at the time of install if the BBA approves it. However,  the case and legalities of aftermarket topups is much more dubious and needs some serious clarification.