Does retro installed Cavity Insulation cause damp?
Having surveyed countless properties filled with cavity insulation I can genuinely say yes, retro installed cavity insulation can cause damp issues to the internally decorated walls.
How does this happen?
First thing to say is, no current or former cavity insulation material used is impermeable yet they the modern materials do have BBA approval. When I say impermeable, that's to say if you soak any of the cavity insulation materials they will retain the moisture like a sponge.
The BBA accreditation's they hold are proof of their thermal values as energy efficient improvements which is why grants are available with them.
"But they are guaranteed installations"!?
Hmm. Sadly, many of the installing companies are no longer in existence. Its not unreasonable to say there are probably more contractors taking the stuff out than installing it. There is an association on hand who will take up a guarantee claim called CIGA but it can be stressful and not as straight forward as a guarantee claim should be.
So why does damp come about because of cavity insulation?
It's my own experience that it comes about for two basic reasons. Firstly, if the construction was not in suitable condition in the first place it should never have been installed. Thereafter, if it was in sound condition, it should be maintained in good order.
In particular, this is in respect of the condition of the mortar between the bricks. If it was in poor condition it should have been re-pointed before the installation. If it was ok but lets say, the property is in a coastal lying region, it needs to be kept in good order to prevent rain water penetrating through the mortar and brick.
Things such as good quality masonry water repellents also help to prevent rain water penetrating but only if the brick face is sound.
There are also bigger issues that to my mind, boarder on neglect and that's when installers block up sub-floor air bricks. I have seen this a number of times and on one occasion, saw that it resulted in a significant outbreak of Dry Rot across the joists and floorboards to 3 rooms including a bathroom which had to be ripped out.
In summary, to answer the basic question, yes, it can cause significant damp issues. In the right property kept in good order, it works absolutely fine and will improve energy efficiency but in the wrong property or a property poorly maintained, in can be extremely damaging.