A relative has lean-to roof. Concrete marley etermit tiles on batons, felt, T&G close-boarded, rafters. 22-degrees. Close-boards stop at the double-brick wall, tiles are then bedded on felt, on mortar, with mortar edging.
Over the double-brick wall at a north-facing corner for about the bottom 15" the mortar is falling out and the felt is disintegrating. Interesting population of woodlice. The result is a damp stained plaster-skim over browning for about 6-inch below and a plywood cupboard has delaminated rather spectacularly over about 3-inches. It is a kitchen below so damp loves company on a north facing wall re dew point. Ventilation is now 220+270m3/hr, open gas appliance removed.
Q - How can I effect a reliable roof repair?
Is it a case of wedge & lift tiles, put impermeable membrane over the wall on mortar, bed the tiles back on mortar. What is the best membrane to use - felt rolls are too heavy for me to handle.
At some point the roof needs redoing with more appropriate low-angle interlocking tiles, I'm unsure if the ceiling fixed to rafters makes that more difficult, but in any case putting the job off a while would be useful since it will be me that has to subsidise. The other side appears ok, at least relatively speaking.