Mossy roof

I thought this roof looked quite pretty but I am sure it is not a good idea to have that much moss on a roof. It would act like a sponge and the water could penetrate under the tiles.  I delivered two clocks in the morning and was treated to coffee, cream and mince pies although I passed on the latter as it was too soon after breakfast.  I came away with three more clocks so I shall not be putting my feet up yet.