Last year in December I went into our attic and discovered the felt on the roof was covered in condensation. We had 6 roof vents installed. After about 3 weeks the condensation had gone. We had no further issues. But I went into the attic yesterday to discover small patches of condensation have returned. the patches are spread out over the felt. There is not one isolated area where the condensation is forming. I am concerned that all the felt will be covered in condensation again as time goes on and the weather is only going to get colder. Any advice because I already have air vents in the attic and there is no water tank in the attic that could be contributing to this issue. There doesn't seem to be any issues with the guttering.
It is quite normal to get condensation forming on the underside of the felt just as it is normal to get condensation on windows in very cold weather.
If you get substantial deposits of condensed water collecting on the floor of your attic then you do not have enough vents installed.
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