Rainwater ingress-Wrong Diagnoses

The client's lenders required a survey to investigate damp to the chimney breast in the lounge which had been identified by the lender's surveyor.

There was evidence of damp staining to approximately 800mm below the joint between the ceiling and the chimney breast. The owners have had the guttering replaced and the lead flashing's at the base of the stack renewed to try and resolve what has been an ongoing issue for a number of years. The have had to redecorate annually to cover over the damp staining. Re-pointing of the chimney stack was next course of action for them when they get some money.

The chimney stack sits at eaves level on the gable end of an 80-year-old bungalow. They had also been advised by a builder that rainwater was running down the flue causing the damp.

I have seen this so many times and thought it would be beneficial to share with those who have not come across it before.

During prolonged rainfall, the stack will become saturated. In a well-ventilated roof void, the water simply evaporates from the stack before it can appear below ceiling level (unless the roof has a shallow pitch). In this instance, the rainwater has migrated through the stack and resulted in damp staining and spoiling of the decoration.

Possible solutions-

• Reduce the stack (if it is redundant) below the roof pitch and piece up the roof.
• Reduce the stack and shroud it with either lead or GRP.
• Line the chimney breast internally with cavity drain membrane ensuring that the abutting timbers and ceiling are isolated from the damp masonry.

It sounds simple but I have seen this misdiagnosed so many times, especially in low roof pitch situations and where the stack sits at eaves level. I hope some find this helpful.

Regards Neil