My parent's house is on the market (Wales) the buyer's survey has shown that the roof pitch is too shallow for the tiles they have for an extension. The roof is 15° and the tiles are recommended for 17°. The overlap between the top and bottom of the tiles is much deeper than the minimum spec though (120 mm vs 100 m) and that seems to have made it workable. DH has taken some tiles off and there are no signs of water ingress - rafters are dry and unstained, underlay is dry and no staining (we figured if water had got in you'd see a water mark). There's even some scraps of paper than got trapped in there when it was being built - again all dry.
Parents shared this with the buyers but the buyers are spooked and want to negotiate on price as they are worried the roof will leak in the future. Does past dryness suggest that it will remain dry? It’s Wales for goodness sakes so that roof has seen some proper wet weather in the last 5 years. Or is that wishful thinking on my and my folks' part? Worst case scenario - presumably it can be fixed by using a suitable underlay?? I don’t want to see my folks sell for under the market price if they buyer is just freaking out about a possible theoretical risk. All of this is happening alongside trying to buy a house ourselves!