Cavity Wall Insulation Advice

8 Sep 2014
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United Kingdom

I have recently removed an old chimney that ran through my bathroom from the kitchen below out through the roof above. The chimney was not large, approximately 12" wide and protruded into the room approximately 6". It ran through the cavity of the wall, but was obviously blocked at either side.

Now that I have removed the chimney, I am going to re-brick to the line of the existing wall. There will therefore be a cavity in the wall as standard.

Although this is only a small section of wall, I would like to take the opportunity to put some insulation in, either fibreglass/slab or PIR board. There was previously polystyrene balls that were installed a number of years ago before I owned the property.


- Do I need to add in a moisture barrier when installing the insulation?

- If yes, which side should the moisture barrier sit, outer wall side or inner wall side?

- Should I leave an air gap or completely fill the cavity depth with the chosen insulation?

- In your opinion, which form of insulation is better?

Any help or advice you could give will be much appreciated.
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