Frosty insulation.

Last December I installed some R-21.5 Roxul (perpendicular to the joist) over the blown in rockwool that filled the 2x6 cavities in my attic. I did what was recommended by the inspector and sealed as many holes as I could find in the attic and installed baffles at every 2nd soffit to ensure proper ventilation. I even took care of weather stripping and properly insulation the attic hatch. Yesterday when it was -25c I check out the attic and was shocked to find that insulation a little bit of frost on top of it. The was no frost on the underside of the roof or rafters. Is this normal? Will the insulation dry out?
Thanks for you help
Marc
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Marc wrote:

At -25 C ~ -12 F it is cold enough for some interesting things to happen. You don't have any bath or kitchen vents into the attic do you?
" installed baffles at every 2nd soffit to ensure proper ventilation." Were there vents in to the outside on the other soffits????
--
Joseph Meehan

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