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Chimneys & Fireplaces

How to ventilate and insulate a capped chimney

I recently moved into a house built in the 1800's. There are 3 floors, with open fireplaces in the ground and first floor. Previous owners have removed and completely capped the chimney above roof level with no ventilation.

There are large patches of damp to the right of the chimney in the 1st and 2nd floor rooms which I assume is caused by condensation. The wall outside is roughcast and appears to be sound.

I intend to plasterboard over the fireplaces and am wondering if I should ventilate the chimney at each floor and in the attic or can I just fill it with vermiculite?

5 Answers from MyBuilder Chimney & Fireplace Specialists

Best Answer

Definitely Vent all fire places and in the loft if the stack has been lowered below roof level, otherwise if you have a chimney pot a pepper pot insert would be my preferred option


Answered 13th Jul 2019

If you cover fireplaces with plasterboard and vent it at each floor as well as attic level this should be enough to allow an airflow circulate in the void .However you should check that the chimney is free from blockages before sealing up.


Answered 13th Jul 2019

I don't think that filling your chimney with vermiculite is appropriate in this situation, it wont make the damp go away. If it is definitely not water coming in from the top of the chimney where they have capped it then i would say ventilation would be your only option to get rid of the damp.


Answered 13th Jul 2019

Hi, uncap the chimney, replace chimney pot, install bird guard on top of chimney pot. At the center of each chimney breast, at about a foot of the ground, install an air brick , there are two sizes, single brick or double brick, decide which is more appropriate and fit.

Mark the wall, using a 12mm drill bit drill out the area within the line,(use the air brick as a template).
Clean the bricks inside the hole, level etc, and cement the air brick in place.
You can use a plastic vent cover to hide the air brick.
It will take a while for the chimney breast to dry out.


Answered 13th Jul 2019

better vent all old fire places with air vents where the fire sat and chimney stack top flues with gas cowls or you will get condensation


Answered 13th Jul 2019

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