In the latest of our technical troubleshooting series, Mat Woodyatt, technical training manager of BMI UK & Ireland, looks at the causes of, and problems arising from, water tracking into roofs.
One of any good roofer’s main concerns – and a roof’s most important function – is keeping the water out, which is why it is very disappointing to get into the loft space and find damp or water damage. There are a number of factors that can lead to the appearance of water on the ‘wrong side’ of the roof – the most obvious being an outright leak.
Unless dealing with an aged roof, it is unlikely that the covering itself has failed. Delamination of clay or slipped or cracked slates and tiles could be the culprits of this type of damage; yet more often than not, the problem is found elsewhere.
If the roofing material appears to be in good shape, then the next place to look is the perimeters and joins. Unsurprisingly, the roof is most likely to leak where the tiles stop and the ‘joining details’ include wall abutments, ridge and verge systems, valleys and hips to name but a few.
Wherever there is a break in the tile coverage, the performance of the roof is dependent on the contractor to properly weather the detail; and, unfortunately, very often the most tempting spots on which to take shortcuts are these details.
Another concern in these areas is where products of multiple manufacturers are expected to interact with each other; and potentially knowledge of all the different product systems – and the skill to fit them – is needed to make them work together. For example, ridge to hip junctions are among the most common locations for roof leaks – and inspections have revealed installation of products from up to five manufacturers: none of which interacting in a way they are supposed to.
If nothing else, that’s a good case for trying to focus as far as possible on a single manufacturer for your full system – manufacturers have taken the time to produce products and rigorously test them to ensure their compatibility and watertightness – to provide both the property owners and contractors peace of mind.
Yet if the workmanship is of high quality, and the roof is in good condition; what else could be causing water ingress?
The next likely place to look is the battens and underlay. In a boarded roof, one needs to check whether it has been properly counter battened to allow the flow of air beneath the roof covering.
On an open rafter system, you need to see whether has the underlay been pulled too tight. An insufficient ‘drape space’ in the underlay between the rafters means that water cannot flow freely under the battens, so it becomes trapped and tracks into penetrations – ultimately rotting the timbers.
Finally, we have to consider the old chestnut of condensation. In a cold roof, care must be taken to properly ventilate. Warm air and moisture rise through the property and when it meets the cold surface of the roof it will condense and work its way back down into the property causing all manner of damage to the timbers and beyond.
The NHBC recommends low- and high-level ventilation in any cold roof system to guarantee the proper flow of air and release of moisture from the roof space. Failing to properly ventilate or the covering of ventilation is one of the biggest causes of water damage in our roofs.
