We have a tongue and groove ceiling and no access to the attic. We used fiberglass insulation in between the trusses when we built our home. We put vents along the roof line. Now when the snow thaws in spring, we get water dripping through the tongue and groove onto everything. We know that we should have put a layer of plastic between the ceiling and the trusses to prevent moisture from going up to the attic, but it is too late now. We really want to avoid removing all the tongue and groove to put up plastic. Is there any other way to create a moisture barrier, such as painting the ceiling with a very heavy duty sealer? Help!

Nope, not a chance. This project was doomed from the start when you installed dimensuional lumber with no barrier. Even removing the insulation and putting plastic between the rafters is not correct. No way to salvage what you have. You could install a visqueen barrier on the bottom side of the T&G and then put another new ceiling on that but what a waste of time and material. Cheapest fix is labor intensive but removing the T&G, install barrier on bottom side of joists and then reinstall the salvaged T&G what there is of it.