I live in a lovely, terraced cottage which has a flat roof just over the entrance hall. The roof is shared with our neighbours. I’ve recently noticed the top of the wall is damp on the side adjoining with my neighbour. What should I do to find the source of the issue and how should I approach it if the damp is coming from my neighbour’s side?
This is something I have seen a few times in the past on similar cottages. Your question doesn’t detail the type of construction of the roof, so for the purposes of my response I’m going to assume that this is a cast in-situ concrete deck which spans both entrances leading into the cottages. If this is the case, the issue is likely to be quite straightforward.
However, the first thing I would advise you to do is to consult your neighbour and explain the situation to them. Even if they are not affected now, it will only be a matter of time before they will be.
A joint approach, including an agreement to split costs, will ensure a comprehensive repair and harmonious relations in future.
Common sense and common interest should ensure their co-operation, but if for whatever reason your neighbour is not minded to work with you on this then I would advise you enlist the support of your roofing contractor – or a chartered building surveyor – to explain to them why the remedial work is required.
If that fails you may need to consider legal options, but hopefully that won’t be required.
I suspect a crack may have formed within the concrete slab – most likely due to expansion and contraction – and now rainwater is weeping through the crack.
These type of roof porches also typically have a flashing/bench formed in mortar at the junction between that flat roof slab and main front wall of the house. This may have cracked also.
In any event, it is likely that a crack/fracture within these elements has led to water ingress and this is now manifesting internally.
The remedy of this defect is straightforward. The concrete deck will need to be cleaned down, and ideally you should have this re-covered using a mineral torch-on felt to seal over the crack.
This would be the most cost-effective solution to addressing the problem and any competent flat roofing contractor could address this for you.
Alternatively, you could also consider having a concrete repair carried out on the roof deck. However, this is likely to be more costly. It would, however, maintain the original aesthetics. Your local building contractor should be able to advise on what is involved.
Whatever approach you opt for, it’s important you and your neighbour are in agreement.
For the purposes of this article, I have assumed a concrete roof deck as this would be typical in those older cottages.
However, if it turns out that this is a timber roof deck then the approach for the repair will largely be similar in that it is likely to be an issue with an old felt roof covering or the flashing detail.
The most cost-effective solution for the longer term would be to simply recover the porch roofs with a new mineral felt and checking and repairing the flashings/bench as needed also.
Aidan McDonald is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland
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