Creekmore Dorset 1960s ex council houses with Stonewold roofing tiles on it . You would of thought there is not much to go wrong with a up and over roof of this age, as it is a straight forward design , however with interlocking tiles th moss can build up and block the interlocking channels which can then ,ake the rainwater overspill on to the undersarking felt.. As you can see from the pics the undersarking felt has more holes than a tetley tea bag and some big enough for a large squirrel or dog to fall through or another creature you might have hiding up in your loft. If your under sarking felt looks like this then you might soon have water ingressing into the property.