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How to insulate a drop ceiling
Ensure that your ceiling tiles can support the weight of the insulation.
Although batt insulation is fairly lightweight, it can put an undue amount of stress on flimsy drop ceiling tiles and break them.
If you have fiberglass tiles, you'll need to replace them before proceeding.
Fiberglass ceiling tiles cannot support the weight of insulation. If you have the more common wood-and-gypsum ceiling tiles, they will need to be at least 5/8 inch (15 mm) thick to be used safely with batt insulation.