chimney damp
Help & Advice

Chimney Damp

What we do with a Damp Problem is try to explain, that the damp is not always directly in the area of the damp patch, it could be:

  • the lead flashing
  • a ridge tile
  • un-felted slate roof
  • missing tiles
  • leaking water pipes
  • the seal around a bath
  • shower or sink
  • frost damaged chimney stack
  • blocked gulley
  • badly fitted or gutter in disrepair
  • the flashing around the chimney pot
  • has a disused chimney not been closed off properly (capped with an air vent)

Signs of Chimney Damp

The signs of chimney damp can be similar to the signs of regular damp, except they all occur around your fireplace or chimney. There may be damp patches on the chimney breast or the ceiling above it, or possibly the walls around it. You might also see staining or discolouration in these areas.

Why Do Properties Suffer From Chimney Damp?

Chimney damp will often occur if your chimney is unused and boarded up. Unused chimneys usually aren’t ventilated properly, so moisture can easily get trapped inside with no way out. If your chimney is open at the top but is not in use, rainwater can travel all the way down to the bottom of the chimney stack. If, on the other hand, the top of the chimney is capped, but it isn’t ventilated, moisture can build up on the inside of the chimney stack, a further cause of damp.

Another significant cause of chimney damp is poor maintenance of the chimney stack, or damage caused by improper building work. Where there are any cracks in the mortar of your chimney stack, water can easily enter through them. If you or your neighbours have had building work carried out on your chimney in recent years and you’ve then developed a damp problem, this is the most likely underlying cause. Some examples of modifications leading to chimney damp include installing a wood burner without the correct flue, or the blocking of ventilation.

What Causes Chimney Damp?

When coal or wood is burned in the fireplace, the tars and salts given off by combustion are absorbed by the flue and chimney breast. These salts are hygroscopic, meaning that they can easily absorb moisture from the atmosphere. Under the right circumstances, this moisture will then spread to other parts of the building.

Even if you haven’t used your chimney in a long time, salts can still remain in the flue from years of combustion residue deposited by your home’s previous owners. The older your house is, the more likely it is that this will be the case, particularly in period homes where fireplaces were used for many years before other types of heating were installed.

What to Do About Chimney Damp

If you suspect you have chimney damp, your first step should be to contact a reputable damp company to have your diagnosis confirmed. You’ll then be in a position to begin tackling the problem. If your chimney is completely unused, it will need to be ventilated at high and low levels to prevent any further damp occurring. You’ll also need to be sure that the room below the chimney is adequately ventilated.

Tracing the Damp Problem

You need to try and trace the problem using a damp meter, like a Rapitest Dtm 118 Damp Test Meter, there are now many more cheaper versions available from, or

Look at the diagram below of how to draw a map to trace the damp:

Then test an area and mark your results on your diagram, this should give you a pattern so giving a good guide line as to the worst damp area, then you can look to possibly finding the cause. This plan can also be used in attic spaces as well, just draw in the timbers and mark the results along them.

In the right hands, the treatment of chimney damp is quick and easy. So call Chim-Me-Sweep on 07879 472119 as soon as you think you have this problem. Our damp specialists will return your home to its usual cosy condition with the minimum of stress and disruption.


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