Cavity wall insulation should only be undertaken after a sufficient CCTV survey. The purpose of this is to identify any mortar snots that lie across the ties inside the cavity between the walls. Builders often forget to remove this excess fallen mortar, which conducts moisture through to the inner wall, causing damp spots to appear on your inner walls. If this inspection is not undertaken properly, or at all in some cases and you are unlucky enough to get damp appearing, then any savings you will have realised from reduced heating bills will have evaporated along with a significant pile of cash for the repair costs.
There are mixed messages in the ether about the true value of cavity wall insulation and even fewer quantifiable/tangible savings figures from those who have had it installed. That is not to say it is not worth having in the long run, but be forewarned, if installed incorrectly or your property is inadequately surveyed then it is a gamble I would wholeheartedly advise against.
More on this topic here: newbielink:https://www.renewableenergyhub.co.uk/types-of-insulation.html#jump_156
[nonactive]Richard.
