Is Damp Coming from My Chimney?

Last Updated 23 August 2018

Damp from chimney

Leaky chimneys are a common source of penetrating damp in the roof of a property. Penetrating damp is especially dangerous in the roof due to the abundance of timber, which is at high risk of developing mould, wood-boring insects and wet and dry rot.

While damp anywhere in a property is unpleasant, damp in a roof can lead to severe structural issues and costly repairs, such as replacing rotten timber.

Here are some of the common causes of chimney damp and the signs to look out for.

Damp from leaking chimney flashing

In a typical period house, the point where the brick chimney meets the roof tiles is covered by sheets of metal called flashing, which seals any gaps between the two and stops water from pooling in the intersection of the roof and the chimney.

Over time, these metal sheets can peel away from the roof or the caulk that forms a watertight seal around the sheets can become eroded. DIY attempts to fix flashing is likely to result in recurring leaks, so it’s best to leave it to a professional company who can offer a long term guarantee on the works.

Leaky flashing is the most common cause of chimney leaks and dampness, the symptoms of which are usually wet, discoloured or dripping roof timbers. If the roof has been converted, you may see the plaster sagging, bubbling or forming mould from the penetrating damp.

Free Damp Survey - Book Today

Damp from damaged chimney stack

Like any other brick wall, the chimney stack is vulnerable to decayed pointing and cracked bricks, which allow water to seep inside the brick and damage them through freeze and thaw.

Many chimneys have been repointed with concrete mortar, which damages the brickwork. Mortar should be soft and porous to allow movement in the structure and for the bricks to release moisture, otherwise you end up with wet, cracked bricks.

You can learn more about how decayed or low quality pointing can result in damp problems here.

A compromised chimney stack can result in roof leaks or penetrating damp. In severe cases, the structure of the chimney may be compromised, though this is very rare.

Damp from cracked chimney flaunching

Chimney flaunching is the mortar or concrete mix that holds the chimney pots in place. If your chimney flaunching cracks, these cracks can fill with water which widens the crack further through erosion and freeze-thaw during cold weather. If the cracks get wide enough, water can trickle down into the chimney stack or down the flues.

Damp from damaged chimney pots or cowls

Chimney pots and cowls are designed to stop droughts and rainwater from entering the flues if the chimney is in use. If the chimney’s unused, the pots may be capped.

If these pots or cowls are damaged or missing, rainwater can trickle down the flues, which can lead to damp and increased moisture levels inside the property, increasing risk of condensation.

You should have your chimney regularly inspected

Chimneys are a part of a building that’s usually out of sight and out of mind, and in most properties it isn’t used at all. This can lead to chimneys becoming seriously decayed before anyone notices, by which point you may also have further property damage from penetrating damp.

This can be an especially nasty surprise for someone who’s about to sell a property, only to find its value significantly reduced by the need for expensive chimney and/or damp repairs.

It’s recommended that you have regular chimney inspections to catch any erosion, damage or leaks early on before they build up into more serious and costly problems.

If you have any concerns about the health of your chimney, feel free to get in touch with us by calling now or requesting your call back today.

How a leaking chimney causes damp issues

  • Flashing (the metal sheets which cover the intersection between the chimney and the roof) can become damaged and allow water into roof.
  • Brick chimney stacks can decay like any other wall, where damp can penetrate into worn pointing or shattered bricks.
  • Chimney flaunching is the mortar or concrete that holds your chimney pots in place. This highly exposed material can wear down and become leaky.
  • Missing or damaged chimney pots or cowls allow rainwater to trickle into the flues, which often goes unnoticed if the chimney is not in use.
  • Damp from a leaky chimney can cause severe damp and rot in your roof timbers, leading to dangerous structural issues and costly repairs.

Need Help or Advice? Then request Your Callback

Holly from environ calling a customer
  • London Based
  • Free Advice
  • All Works Guaranteed
  • Friendly Service Team

Here are some helpful related articles

Damp Proof Paint is Bad For Your Home

Waterproof paint on exterior brick walls doesn’t fix damp in period properties. In fact, it can make it much, much worse. Find out why, and what to do instead.

Damp Proof Paint is Bad For Your Home

Should I Paint Over My Damp Walls?

Damp proof paint has its uses, but by itself it can’t fix most damp problems. Learn about three types of damp proof paint, what they treat and what they won’t.

Should I Paint Over My Damp Walls?

What Causes Lateral Damp?

Lateral damp is caused by groundwater which has saturated your walls or floors. It’s most common in basements and more severe in areas with a high water level.

What Causes Lateral Damp?

What is Lateral Damp?

Lateral damp is common in basements, where groundwater seeps through the walls. If untreated, moisture-attracting salts from soil accelerate the spread of damp.

What is Lateral Damp?

What is penetrating damp?

Penetrating damp is damp which comes from exterior defects or leaking plumbing. If left untreated it can lead to mould, rot or even dangerous structural issues.

What is penetrating damp?

What Causes Penetrating Damp?

Penetrating damp has many causes, from plumbing and drains to tiles and cracks. Some can be fixed with a bit of DIY, others require a help from a professional.

What Causes Penetrating Damp?

Pointing causing damp

Is My Pointing Causing Damp?

Decayed or poor quality pointing damages bricks and leads to penetrating damp. Read our blog to learn how to spot problem pointing and how it harms your walls.

Is My Pointing Causing Damp?

Damp advice

How To Avoid Damp Scams

During many of our damp works, we discover properties that have fallen victim to damp scams

How To Avoid Damp Scams

How to treat penetrating damp

How To Treat Penetrating Damp

Penetrating damp needs to be treated ASAP to prevent property damage and mould. Read our blog to find out how we identify, treat and repair penetrating damp.

How To Treat Penetrating Damp

Basement damp

Why is My Basement Damp

In London, it can be difficult to find the room or get permission to extend your property. This means that more and more people are turning to their basements for extra space.

Why is My Basement Damp

Rising damp causes

What Causes Rising Damp?

Rising damp worrying you? Learn how to identify rising damp and what causes it in this blog by damp expert and Environ Property Services founder, Terry Clark.

What Causes Rising Damp?

How to treat rising damp

How To Treat Rising Damp

Find out how to spot rising damp, what causes it and the best way to treat it with this handy guide from Terry Clark, damp expert at Environ Property Services.

How To Treat Rising Damp

How To Treat Lateral Damp

What is lateral damp, how can you spot it and what’s the best way to treat it? Answer all these questions and more with our guide from damp expert Terry Clark.

How To Treat Lateral Damp


4.80 Average

128 Reviews


Highly recommend this company! After we travelled back through Asia we picked up some nasty little critters, however Environ came out and with no …

Esther W

Over moon pest free! Highly recommend this company to anyone who has a pest problem, we travelled back from Manialla and picked up some very pesky …

Frank McL

Emily has been very responsive in getting visits to me before Christmas to sort out a rodent problem. We had our first visit from the technician ( …

Holly is available to take your call

Call Holly