Insulation, Radiant and Vapor Barriers - Question about insulating above a drop-ceiling .

I have a Mobile Home where the living room has a cathedral ceiling (center of the Home). Im having someone put in a 2x4' lay in tile ceiling grid right now as i type this -- im having this done to decrease the amount of heat gain/loss and thereby reducing heating/cooling equipment runtime . The center height above the drop ceiling will end up being 2' and a steadily decreasing height to the outer walls . I want to insulate above this drop ceiling, and need to know if its better to insulate all the way up to the inside of the roof leaving no air space, or, to allow a certain air space ? Im going to use Batt insulation. So, which is more effective -- air space or no air space and why ? Thanks. David.

Hi David, I have some concerns about your project, but they depend upon where you are. In a cold climate, one has to be careful with multiple layers of insulation. Example, a closet with the back wall to the outside can experience condensation and mold when the door is closed. Reason is the interior warm moist air still enters the closet, but the door blocks enough of the heat to allow the rear wall to drop below the dew point.

Both of your proposals will result in warm air flowing up through the ceiling and insulation and reaching what will now be a much colder old ceiling. Condensation is most likely with the potential for mold to follow.

Now, I'll take a stab at what to do, but hopefully those better qualified will jump in. You need some sort of air barrier on the warm side of the insulation and a drop ceiling doesn't make that easy. If you places a 2" layer of rigid insulation up against the old ceiling and did not insulate directly above the drop it might work, but you need better advice then mine.

help
Bud

Hi David, I have some concerns about your project, but they depend upon where you are. In a cold climate, one has to be careful with multiple layers of insulation. Example, a closet with the back wall to the outside can experience condensation and mold when the door is closed. Reason is the interior warm moist air still enters the closet, but the door blocks enough of the heat to allow the rear wall to drop below the dew point.

Both of your proposals will result in warm air flowing up through the ceiling and insulation and reaching what will now be a much colder old ceiling. Condensation is most likely with the potential for mold to follow.

Now, I'll take a stab at what to do, but hopefully those better qualified will jump in. You need some sort of air barrier on the warm side of the insulation and a drop ceiling doesn't make that easy. If you places a 2" layer of rigid insulation up against the old ceiling and did not insulate directly above the drop it might work, but you need better advice then mine.

help
Bud

Thanks for responding. I live in Florida and the average low temp. in the winter time is 40 f. On the other side of the room is a bathroom/bedroom/and kitchen. Ill wait for others to reply.

Florida, that's good, now the conditions are reversed, which may work out better. Since the space above the new drop is/was actually living space, then there should be minimal outside air filtering in. In warm climates it is the warm moist air coming in contact with cooler air conditioned surfaces, which your new insulation will be helping to keep separated.

As for an air space or not, not required. You can install as much insulation as will fit, avoiding compression of course.

project may continue,
Bud