Every winter iget this problem, condensation on the roof felt and on the wooden rafters.-I have installed sofic vents 4 one side 6 otherside, and have a extractor fan running twice a day for half an hour, but still have the problem. Would air bricks help and is the condensation bad enough to rot the rafters if so how long!! also would it be a good idea to insulate between the rafters and cover with builders paper or something similar. any comments and ideas welcome, before it becomes too costly
Your have condensation in the loft because it is winter, it is cold and you are producing a lot of water vapour in your home.
Water vapour comes from washing, cooking, breathing, drying things on radiators.
It gets into the home because people leave doors open.
If you have extractor fans in the kitchen and bathroom use them, in any event keep the kitchen and bathroom doors closed, open a window to let the water vapour out.
Check that the trap door into the loft is properly closed.
Water vapour can and does move up through holes in the ceilings, it does move through plasterboard ceilings and through the fibre glass insulation above.