Doubling the thickness of insulation will double the insulation's R-value, cutting heat loss in half. Each time the insulation layer is doubled in thickness, this rule applies. ... In some cases, like an attic, it's worth piling on more insulation because there is plenty of room.

Is it OK to stack insulation?

A: There's no problem with installing fiberglass batts over your existing blown-in insulation. ... If you install faced insulation over existing blown-in, you're essentially putting the vapor barrier in the middle, between the two layers of insulation.

Can you put two layers of insulation in walls?

You probably already have insulation in your walls and attic, but maybe you're wondering if you should remove your current insulation or add new layers over the old ones. So, can you install attic insulation on top of old insulation? Put simply, yes.