Cavity wall insulation and electrics

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Cavity wall insulation in the consumer unit.


Electrics running in the cavity has always been seen as dubious and not part of best practice but the fact is older houses can have large amounts of wires within the cavity which needs to be considered during retrofit cavity wall insulation.
Building regulations are clear that before installing cavity wall insulation any wires in the cavity should be identified and dealt with, preferably re-routing them.  

Although BS8208 has been withdrawn. Thee majority of historical CWI installs were done with Agremént certificates which conform to this standard: 

BS 8208 Part 1, 1985: Assessment of suitability of external cavity walls for filling with thermal insulants. "Where they cross the cavity. Cables may need moving or uprating before a cavity is filled (they can overheat if surrounded by insulation)."

There is a significant expense in  recruiting the services of an electrician while doing a CWI install and it may cause significant delays to the IAA's '2 hour install time'. If  the cavity is carrying large  number of wires to the upstairs then it could becomes a partial re-wire to sort out the wires which could easily cost more than the rest of the insulation.
Aside from the integrity of the electrics.  Long runs of wires in the cavity can cause large filling voids and moisture bridges as documented in earlier post .

Clearly the strategy which many installers take is to just ignore the wires and pump the product in hoping that no one would notice. As with many CWI. Failures resulting from such short cuts can take many years to materialise and the installer has long gone bust.

Bonded bead finds holes in the inner leaf.  Was this missed in the pre installation survey or is the survey completely inadequate?( Image from  @brad_electrical)


One home owner thought there was a clutch of eggs in the consumer unit and asked for help in identifying the species.

Dotted pattern showing damage to PVC cables from contact with the beads. 


Interestingly with the green home grants. BEIS is keeping an eye on costs and rejecting quotes which are seemingly too high compared to competitors. While it is designed to spot fraud it may also encourage short cuts, especially ones which are difficult to detect from a 'desktop audit. 'Right first time' would mean paying attention to details such as electrics and we should expect some Green home grants to have addition work billed for electrician's services

Electrician John Ward explains the problem and how he dealt with sorting out such an issue in the video below. The only issue is that this could be classed by CIGA as disturbing the insulation which is enough for them to declare the guarantee void should a separate issue be found in another part of the house in future. 


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