Another important note. You want insulation on top of the attic access. An uninsulated attic access cover can reduce the average insulation value of your entire ceiling of up to 25%. I prefer using polyisocyanurate foam that is glued down so that you don't have to deal with juggling a section of batt insulation.
Just to add here, of course conditioned (so warm air) rising from the house in winter can cause this frost. But to simplify it, it’s too much heat on the attic regardless of the reason. Even with a properly weatherstripped hatch this can happen. Bad air sealing at plumbing and electrical runs etc, and bad air sealing at the hatch. But also just not enough venting. Regardless how well you air seal, how much insulation you put, all you are doing is slowing down the transfer of heat - not stopping it. Regardless how much you air seal and insulate you need proper venting. If the attic is warm, and the outside is cold, the only barrier (roof plywood/shingles) will form condensation on the warm side - so attic side. And when it’s cold enough, this condensation then freezes and you’ll get this frost.
Another important note. You want insulation on top of the attic access. An uninsulated attic access cover can reduce the average insulation value of your entire ceiling of up to 25%. I prefer using polyisocyanurate foam that is glued down so that you don't have to deal with juggling a section of batt insulation.
Great point. Thanks for commenting.
Just to add here, of course conditioned (so warm air) rising from the house in winter can cause this frost.
But to simplify it, it’s too much heat on the attic regardless of the reason.
Even with a properly weatherstripped hatch this can happen.
Bad air sealing at plumbing and electrical runs etc, and bad air sealing at the hatch.
But also just not enough venting. Regardless how well you air seal, how much insulation you put, all you are doing is slowing down the transfer of heat - not stopping it.
Regardless how much you air seal and insulate you need proper venting.
If the attic is warm, and the outside is cold, the only barrier (roof plywood/shingles) will form condensation on the warm side - so attic side.
And when it’s cold enough, this condensation then freezes and you’ll get this frost.
I caulked my attic access because it is full of asbestos.