There is rainwater leaking into the chimney breasts over our bungalow

March 2014

Question

We have a problem with rainwater leaking into the chimney breasts in our bungalow. The water is soaking down through the concrete blocks, causing the paintwork on the chimney breast walls in the rooms below to bubble. This has happened before, about three years ago. We had previously removed a fireplace and closed up the opening. We also sealed the chimney pot. This work was done about seven years ago. Our house was built in 1977. Can you help us?

Answer

You do not say where the chimney is located, at gable end; along the ridge or at eaves’ level. What is the finish above the roof, plaster or brick? The top has been sealed to shed water away. How was it sealed and was the pot removed? There should be a damp proof course (dpc) underneath the capping to deal with any moisture absorption. Also further down at the chimney and roof slope junction, a dpc tray should be installed, to prevent moisture ingress from cracked or porous plaster, brickwork, pointing and poor lead detailing. Part of the dpc tray can sometimes be seen in the attic. If no tray was installed, then moisture can penetrate. How are the outer lead upstand and cover flashings constructed? There should be minimum 150mm upstand height for the lead plus an adequate lead back gutter.

If the angle of roof pitch is very low and there is insufficient head lap of the slates then driving rain will enter particularly at exposed locations. Any holes in the roofing felt under will provide a path for rainwater. Check this along with the chimney and the felt junction. The felt should be dressed up under the outer lead which is sometimes omitted. There may be other factors at play such as condensation or porous plaster on the outer wall to the chimney. The enclosed chimney space should also be vented.

In a dry spell you can test the roof finishes with a water test and by a process of elimination you may be able to identify the point of entry. This would require a controlled even spray by an experienced roofer in the presence of your professional advis er. I would really need to know more about the chimney and roof construction and therefore recommend that you seek advice from your local chartered building surveyor. An inspection at roof and attic level along with a check on the surrounding roof construction may identify the problem, before any testing is carried out. Even better, if you can coordinate this by providing safe access for the surveyor onto the roof.

Jim Drew is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland .