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Remove and Re-insulate Cavity Walls G#731 N#753

By 15 July 2014November 22nd, 2018Uncategorized


Remove and Re-insulate Cavity Walls 

Remove and Re-insulate Cavity Walls


My colleague and I have attended your talk at launch of the AECB EofE Group in Cambridge and were wondering if you can help given your immense knowledge of various construction materials and products.
We are involved in a house extension and upgrade project where the clients are proposing that we fully fill the existing cavity wall with spray applied closed cell polyurethane foam insulation
  • GBE CPD BIM A Spec Writers Perspective (Shop) G#11814

which we have never used before. The cavity in question is already insulated with stone mineral fibre
  • GBE CPD BIM A Spec Writers Perspective (Shop) G#11814

, which will have to be taken out before the foam is sprayed in.  From the various online threads we have been reading, it seems that spraying foam into an existing cavity can lead to problems in the long run especially when this is not installed properly.
Have you come across this type of insulation before and are you aware of any impact on the existing fabric?  We have contacted [manufacturer’s name removed] and they confirmed that they have not monitored any of their projects after installation. They have applied for BBA certification but this is still pending after 2 years.
If you can kindly give us your view on using this type of insulation and/or direct us to any studies that you know of, that would be greatly appreciated.

Thanks in advance for your assistance.

  • I have never heard of insulation being removed from a cavity,
  • Is there any equipment? probably no
  • Is there anybody who can claim to be capable for doing it? probably no
  • Will [manufacturer] or an installer sign off the state of the cavity knowing it was previously filled and allegedly now empty? probably no, but willing to be corrected
  • Will you do an infrared survey to see if the insulation is removed thoroughly?
  • Will [manufacturer] and/or the installer stand by their guarantee if the cavity is not 100% clear? Unlikely but willing to be corrected
  • If asked would they sign a Declaration of Conformity?
  • If asked would that sign a Manufacturer’s review of proposals?
  • Will you [architect] sign off the cavity is clear?
  • How will you ever know?
  • Will the Building Inspector sign it off?
  • Will a judge rule in anybody’s favour?
  • Is this just wishful thinking on the part of the client, that you should be steering them away from?
  • You have a ‘duty to warn’ your client that this approach is highly problematic.
  • Who said spraying in stone mineral fibre is free of problems?
  • Have you carried out an Infra-red thermography survey of the wall with the stone mineral fibre in place?
  • Mike Malina, in AECB East, could carryout such a survey for you.
  • Mike Malina <>
  • All spraying of insulation into cavities is potentially problematic and rarely checked by IRT survey.
  • When checked it will probably be found wanting.
  • Will you repeat the IRT survey at the end to see if the PU is done well?
  • You PII provider will advise you not to go to [manufacturer] until they have an Agrement Certificate
  • Two years in the making suggest there may be a problem.
  • Does the Certificate say it can be use in previously insulated cavity? Probably No or silence.
  • PU foam is used in SIPS
  • PU is closed cell probably moisture impermeable (vapour closed) so it will change the dynamics of the wall which is currently vapour open with (assumption) highish resistance gypsum plaster inside, (Unknow block type) vapour open cavity insulation and vapour open outer leaf.
  • PU is probably hydrophobic so will stop rain getting in to cavity and prevent access to inner leaf unless the insulation is patchy.
  • I do not know of any studies but BRE digests must cover it if its not a new invention by [manufacturer].
  • I hope I have convinced you, that you should not be doing this.


  • If you are determined, warn your PII provider in advance, see what they say.

Sorry to be unhelpful, but I hope you will agree in the end this is helpful.

28 Jan 2013 – 22nd November 2018

Remove and Re-insulate Cavity Walls


28 Jan 2013 – 22nd November 2018

Remove and Re-insulate Cavity Walls
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© GBE NGS ASWS BrianMurphy aka BrianSpecMan
28 Jan 2013 – 22nd November 2018

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