I thought I had fixed a leak, but the water has returned. What should I do?

Property Clinic: An inspection by a building surveyor should help diagnose the problem

My query is in relation to an external water leak when it rains. The property is about 15 years old. I noticed water dripping from the top corner of a ground-floor window. Closer inspection revealed a 25cm-long narrow crack (stretching outwards and upwards) in the external plaster at the top corner of the window frame/reveal. There is no evidence of water on any internal walls.

I had the crack filled by a tradesman, but this doesn’t seem to have sorted the problem. I’m wondering what my next step should be and would welcome advice.

Your property is relatively new and the type of cracking you mention is typically associated with initial settlement of the building. Filling of these settlement cracks to prevent direct water ingress is the correct approach. And, as with any ailment, a full assessment is needed to pinpoint the problem. Leaks are an indication but in some instances the issue can be remote from the area where the leak appears.

I have seen leaks show up on ceilings where the water has travelled along concealed steel beams in the ceiling void. In that particular instance, it was only after localised roof repairs above the damp area failed to address the problem that the ceiling was opened up and the source of the problem identified. Water was travelling in the web of the steel beam and leaking at a fixing many metres from the roof leak.

I have also seen another case where water used during construction was trapped in the voids of a precast concrete first floor. A leak persisted here for many months and baffled all who tried to diagnose the problem.

Your external walls are plastered or rendered. Masonry walls with a render finish allow an amount of water to enter their fabric and this dissipates slowly through evaporation. In extreme cases or where an elevation is exposed or west facing, the walls can become saturated and water can actually enter the cavity that exists between the inner and outer leafs of the external wall.

When this happens, water will travel down the cavity and egress at the base of the wall. Where windows and doors are concerned, a damp-proof course (DPC) will be provided above them to capture this water and direct it away from the opening. If this DPC was not installed, water would simply escape at these openings and enter the building. Sometimes these trays can be poorly installed or omitted altogether, leading to the type of issue you describe.

As I mentioned above, a good, detailed inspection and assessment will help in reaching the correct diagnosis. You haven’t mentioned if the leak coincides with rain. Are there any waste pipes or rain water pipes concealed in the wall fabric? Are any overflow pipes present above the area that may be directing water into the external wall? Are there weep holes in the walls to allow water to egress and evaporate? Could there be an issue with condensation? All these matters need to be considered.

It sounds to me like there is an issue with the formation of the DPC above the window, but an inspection is needed to determine an accurate diagnosis and correct remedy.

You are fortunate that the water does not appear to be reaching the inside of your house. Still, as with any water ingress issue, swift action will reduce the extent of damage and ultimately the associated cost of repairs. Your local chartered building surveyor will be well versed in dealing with this type of issue. – Noel Larkin

Noel Larkin is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland, scsi.ie