Repairs: roofs and rainwater goods

If there is no obvious route for water entry, check the tile gauge, i.e. that there is sufficient lap for the specification and size of tile being used. (Sometimes there is a temptation for the roofer to open up the gauge and save a little bit of money and weight.) You will need a long ladder to investigate, unless you can pull away a section of roofing felt from inside the roof (which usually needs permission from the owner).

As well as resisting driven water penetration and helping to even-out wind loads through the roof, the felt laps into the gutter to prevent accelerated decay to the timbers beneath. However, traditional felts can soon decay from solar exposure, causing the edge lapped into the gutter to deteriorate. There is a proprietary plastic eaves detail now available from some u-PVC window and cladding manufacturers, and this profile can be sleeved under a deteriorated felt edge and into the gutter if only a small and relatively localised felt repair is needed.

Where there is a particularly aggressive and wet climate, counter-battening helps to ensure any driven rainwater is drained away over the felt should it penetrate under the slate covering. This also reduces the risk of the battens rotting if moisture becomes trapped between any poorly set sections of roofing felt that may be trapped under a conventional roofing batten.

Note: adjust the tile gauge to prevent driven rain penetration. The felt will help protect the roof from moisture, but its primary function is to control the effects of wind load and suction on and through the roof.