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Cavity wall house: insulate external only or external plus cavity?

We have a cavity wall detached house (built '76) on Anglesey. We are in an exposed position and get a lot of wind driven rain (storm driven rain is closer the mark). The house has had render problems from new (something to do with salt in the brickwork leaching out?). We have wind driven rain coming in around windows (sides and centre of lintel). We get mould on walls in certain corners . The cavity has not been insulated.

I now intend to get new windows fitted and the rendering re-done. I'm tempted by external insulation (I read that its guaranteed to stop water ingress). My question is: should I also get the cavity insulated at the same time? Would leaving the cavity empty undo the benefits of external insulation?
Are there any other options I should consider?
Many thanks

1 Answer from a MyBuilder Insulation Installer

Best Answer

if you seal the property too tight you are at risk of getting condensation dampness unless you have inserted adequate ventilation. it may stop damp penetration but it will cause extra dampness internally.

Externally, you should use a water REPELLENT. This does not seal the wall but allows vapour to pass through without letting rainwater in.

Cavity wall insulation can be beneficial if carried out correctly and ventilation has been addressed within the property to compensate. Another check to make is that the walls are dry before inserting cavity wall insulation otherwise this will hold the moisture making the walls internally worse.


Answered 20th Sep 2016

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