Moss had built up on a interlocking marley modern tile roof causing rainwater to drip on the underfelt. overtime this damaged the felt and it will finally fail. we looked under roof tiles and could see the last 2 rows of felt needed to be replaced. we set up a scaffold and removed the tiles and set aside for refitting. we then replaced the felt with a modern breathable roofing felt and refitted the tiles. all the moss was removed from the tiles to prevent from future damage.