Air sealing around can lights. Ideas?

[herlichka]

It is actually the vapour that you want to stop: if water vapour is allowed to travel from the warm interior of your home into the insulation it will eventually reach a point where it is cool enough to condense. This condensation will eventually cause mould, mildew and will cause structural decay. This is why we install a vapour barrier on the "warm" side of the wall, and a house wrap such as Typar or Tyvec on the outside. The house wrap is an "air barrier", it prevents wind and wind driven rain from penetrating into the wall from the outside, but does allow the insulation's accumulated moisture to dissipate to the outside. Moisture can accumulate simply from the change of seasons, and the moisture content of the outside air. To deal with the moisture inside the house we must install some form of mechanical venilation, and/or a Heat Recovery Ventilator.

I have seen horrendous water damage inside the cavity of exterior walls adjacent to kitchen, bath or even laundry rooms, caused not by actual water penetration, but condensation from moisture seeping out to the cold side of the insulation. I have even seen ice in the insulation above ceiling light fixtures in the attic, from moist air traveling upward from the interior of the house through the electrical devices. Our winter temperatures in Ontario can drop to -30c or more for extended periods, so these ice deposits can become substantial in size, and when the temps rise and the ice melts the wall surfaces can be damaged, people often think that they have a leaky roof.

All for the price of a roll of plastic and a roll of tape.