What could be the cause of water ingress at a verge?
Placing the undercloak under the underlay at the verge can be the cause of water ingress to the roof because the bedding mortar is not truly waterproof. Under driving rain conditions water can run onto the undercloak behind the mortar. The quantity of water will increase if a hairline crack between the mortar and the undercloak or roof tile exists. Once the water is on top of the undercloak it may run down the roof slope. If there is a fall in towards the roof water can run off the inner edge of the undercloak. It may run under the underlay into the roof or the brick cavity. If the undercloak is placed over the underlay water will run onto the top of the underlay and down to the eaves. If the underlay is placed over the undercloak and is allowed to come into contact with the mortar, water can be sucked in through the mortar and create a slip plane between the mortar and the undercloak. By keeping the underlay under the undercloak this will not happen. It is essential to finish the unde
