Causes of Moisture Around Recessed Lighting
Common problems from improper insulation material use and type include can or pot lighting. The heat from the pot light collides with the cold from the roof deck forming condensation. The larger the difference in temperature, the more the condensation. One aspect of this type of problem in a flat ceiling (pictured above) or cathedral ceiling is there is not much that can be done to remedy this problem because of the lack of space available in the cavity making this a very messy fix.
Getting Proper Insulation and Air Sealing Above the Pot Light
If there is no room to get into the cathedral attic, then the only way to properly insulate is from below by drilling holes in the ceiling for access. Then a professional insulator can insert a hose and use pour-in-place foam to insulate air seal the light. Generally 2 holes will have to be drilled one above and one below the light. This will stop the transfer of energy and moisture issues that exist. Please not that this type of foam is water based and may react with any moisture that is currently on or in the cavity. It is recommended to make sure that the area to be foamed is dry. After the insulation is injected, the holes can either be plugged and patched if the ceiling is drywall, or the hole can be plugged with the original plug that was taken out and wood filler can be used to fill the small gap that is present.
Using this method WILL NOT save any energy but will keep your house healthy for years to come. To save energy, have the insulation contractor use dense pack cellulose on the main portions of the ceiling for maximum air sealing at the lowest possible price point.