I have a garage cum granny flat 17 metres long by 4.5 metres wide the entire ceiling has fibreglass insulation and the floor of the attic is covered with timber wood chip sheets 8 ft by 4 ft. The space in attic has only slight standing room in the centre. The granny flat is not used the entire winter. I was considering insulating in between the rafters just under the felt. Is it worth it.Will it just make my attic warmer and not the rooms below the ceiling.The cold water tank frooze recently, no damage done. Pipes are lagged but the tank was nt insulated. Should I just insulated tank only or try insulting under the felt.Which material would be best. Can sheepwool be used in this area?What about condensation under felt when weather is very cold outside. Would prefer not use fibreglass. Is rafterlock an option?The entire roof area is 70 metres square> Any advice welcome.