We were asked to investigate this leak. It turned out to be due to condensation. The pot lights were added much after the construction of the house, and the installer did not use an air-tight insulated box for each light. As a consequence, warm and humid interior air entered through the pot-light enclosure into the ceiling cavity, and with minimal insulation left (because it was mostly removed to make room for the pot lights), there was a LOT of condensation.
The do-it-yourself remodeller also made similar mistakes elsewhere in the house, piercing the vapour barriers, and not allowing any air circulation above the insulation. As a result, the interior air infiltrated the cold spaces and almost “rained” condensation into the interior.
In the section https://prsconsulting.wordpress.com/links-and-useful-information/, there is a link to a very good article in Fine Home-building Magazine which discusses ventilation issues and has some nice diagrams showing show how the ventilation should work.
We also have had reported leaks in bathroom fans, which turned out to be condensation, and other “leaks” which turned out to be condensation from poorly insulated air ducts conducting cold air (in summer, obviously). So when you spot a “leak”, it may not be what you think it is. Time to do a little sleuthing.
(c) 2013 Paul Grizenko