Condensation after cavity wall insulation can be a major problem. Many people have experienced huge condensation problems after installing cavity wall insulation.
Cavities have been used in building practice for hundreds of years. The idea of having a cavity between two building layers is for air to circulate – to allow the internal wall to have no contact with the outside wall so that the elements do not come into contact with the internal wall. Makes sense doesn’t it?
When you install cavity wall insulation you block the airflow between the walls and the roof – you also block the airflow from the subfloor if you have one.
You also allow the outside wall to come in contact with the inside wall, so what effect does this have?
Well if you block the subfloor from rising to the roof, moisture under the floor will stay under floor and you will have rising damp, a big under floor problem.
If you allow the outside wall to come in contact with the inside wall any wall ties that hold the outside wall to the inside wall will be allowed to rust away from moisture sucked through from the outside wall, penetrating dampness and unfilled air pockets leaving cold spots on the inside walls will attract condensation.


With the roofspace locked up and the walls blocked up what do you think is happening in the roof – massive condensation problems. It will be raining in your roof causing dry rot to the building materials, water soaked insulation rendering its R value useless. Worst of all the added moisture will be the cause of mould and mildew problems which can lead onto SBS (Sick Building Syndrome) also look at our BLOG – “Warning Read This Before You Design Your Next House”.
So think twice about installing cavity wall insulation result no subfloor dampness – no inside wall dampness – no condensation.
Leave the cavity there, it is there for a reason.
If you effectively ventilate your roofspace you will find that any value received from cavity wall insulation will be far exceeded by proper roof ventilation and won’t cost you anywhere near as much.


To allow air to rise from the subfloor or the slab, to rise up through the walls into the roofspace and out of the roof ventilation, this has worked well for hundreds of years so it is best to leave well enough alone.
With the air rising, due to friction, when it is cold it will be warm and when it is hot it will be cool. It is obvious it was designed for a reason so why try and fix something when it is not broken.

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