A common cause of water in the loft during winter months is rain driven in by the wind, usually due to a lack of felting under the tiles or slates. To prevent further penetration, use building paper. This is bitumen-impregnated, and so is waterproof. Pin the building paper in horizontal strips to the rafters, starting at the top and working down. Allow a good 6in/150mm overlap between the strips and seal the joints with water-proof clear adhesive tape. Use brass drawing pins to fix the paper in place. Slip the end of the building paper out under the eaves so that any water collected is directed out of the house.
Treat a felt or asphalt flat roof which develops cracks with brush-on liquid rubber. You can apply the rubber with an old, large paintbrush or a small broom. Clean the roof of any loose dirt or chippings beforehand.
Repair fine cracks in the felt with a bituminous sealant, which fits into an applicator gun.
