Ask an expert

Get free help from our community of tradespeople

Capping a chimney

Posted by David Draper, on
I have a twin chimney stack but one side is no longer used and I want to cap it off. I am getting conflicting advice from builders/roofers about whether the cap can be a complete seal, or whether it should be vented to allow a small amount of air circulation. What is the approved best practice?
sam boswell

sam boswell

Hi, unless your going to cap both sides, I would recommend using a vented cap. that way the other side wont cause condensation and rot the brickwork. Regards Sam
(3) Was this helpful?
David Halliday

David Halliday

Hi david, If you plan on capping your chimney you should always vent the flue. The best practice for this is to fit a vent at the wall where the original fire would have been and to fit a vented cap on the chimney stack at the chimney can that way it allows for free air circulation around the inside walls or as we call it the flue. The reason been is that if you don't allow the free passage of air you can end up with condensation and all other sort of nasties that can occur in time. When your builder does the work get him to carry out a smoke test to make sure that all is fine. This is done by placing a smoke pellet up the opening and making sure everything is in place. Good luck with your project, Dave Halliday Edinburgh Stonecraft.
(2) Was this helpful?
Chris Plastow

Chris Plastow

I fix the problems caused by not ventilating capped chimneys , condensation will build up in the flue or even in the remnants of a chimney through the absorption of moisture to a chemical within the brick work called ammonium sulphate. If you don't ventilate top to bottom, it will cost you plenty to re render the interior later.
Was this helpful?

mark andrew bond

Hi david I would recomend a vented cap and some form of air brick at base of chimney where fireplace was to allow for proper ventilation of stack
Was this helpful?
Michael Tucker

Michael Tucker

Hello David, You can cap your chimney off but you will need to introduce an air brick to the chimney. Regards Michael
Was this helpful?
Louis De Courcey

Louis De Courcey

I would just cap it off , but it would do know harm to vent it , as both options are correct . I know it doesnt really answer your questions but it is one of those situations where both are correct.
Was this helpful?

What would you like to do now?

Find more questions Create my Job

Homeowner stories

Homeowner stories - Nick

Nick shares his story of finding local tradespeople in his new area.

app-icon

Get our app for homeowners

  • Send messages and get notifications from tradespeople
  • Add photos to get more accurate quotes
  • View tradespeople’s profiles