A friend purchased a house approx 20 yrs old. The house had a missing slate and there is rot in the roof timbers. They have had a builder in to look at it and the costs for correcting the problem are quoted at 4500e. My question is should the engineer have spotted the missing the missing slate from an external inspection, and/or should the rotting roof timbers have been spotted in the loft inspection and if so is the engineer liable for cost of repairs. I'm told the engineers report mentions that he is not liable for hidden defects.