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With this recent blizzard we recently saw our ceiling lighting fixture leaking water (slow, about 1 drop every 5 minutes)

I got up in the attic and saw that some snow had been apparently blown into the attic through one of the vents. I removed about 2 handfuls of snow from on top of the insulation, but 2 of the pieces were still damp. Should I remove them? Or will they dry up soon enough? Are there any problems with that?

Also, should I do something to seal up the electrical box from the attic?

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If your insulation is damp, chances are good it could freeze or stay damp for a while. If not too much is involved, it would be a good idea to remove it to a warm place to dry out, or simply replace it. Never a good idea to leave wet material against ceiling drywall. It could dampen and ruin the drywall. If left too long, mold or mildew could result. The snow coming through the vents is probably an isolated event. Don't close the vent. Maybe just lay a sheet of 4 mil plastic over the insulation to keep snow off your insulation. Keep an eye on it. If it happens often, consider a better louvered/screened vent fixture that won't allow snow to blow in as easily.

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    Depending on if there is a vapour barrier under the insulation, putting plastic sheet over it may make the problem worse. If the insulation has no vapour barrier under it, warm wet air from the house may be moving through the drywall celling and into the insulation. This can in some cases cause small amounts of condensation within the insulation. However, when the weather is warmer the insulation will generally dry out again, being removed by the loft ventalation. If it is covered in plastic then this drying out may not be able to occur, as the plastic will hold any moisture in the insulation.
    – flamingpenguin
    Commented Feb 3, 2011 at 14:26
  • I was only meaning to put some plastic down to stop snow from comming in contact with the insulation, not as a vapor barrier, It can be removed when repairs are made to vents. Talking a small piece of plastic here.
    – shirlock homes
    Commented Feb 19, 2011 at 21:50
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Some types of insulation will not insulate effectively when they are wet. The insulation could grow mould and the water could damage other materials that it comes into contact with such as the the wood fabric of the root, or the ceiling. I would definitely try to dry it out or replace it. Make sure you use appropriate safety equipment (gloves, correctly rated mask) if you touch or move the insulation.

I wonder, if snow is able to be blown in through your vent then can rain also get blown in that way? It might be much more difficult to notice the effects of that as it would be more gradual rather than all melting at once and running though the ceiling, but over a long period the dampness could damage the wood in your loft, the insulation or other materials. I would look into having the vent replaced with one that prevents water getting blown in.

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I think it depends on how wet it is and how long it will take to dry out if you do nothing.

We know it is above freezing point in your loft, as otherwise the snow would not have melted. Assuming you have good loft ventilation and hence air movement above the insulation, it will dry out.

If the insulation is only damp rather than wet, I would do nothing at present, and then check it in a few weeks’ time to see if it has dried out.

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