Which side does the foil go on insulation, which side faces out, and how do you lay foil backed underlay?

Regardless of whether fiberglass insulation is installed in a wall, attic, or crawlspace, the paper facing should always face the inside of the home.Water can't pass through the paper because it has a layer of asphalt glue.

What do insulation boards do with foil?The board faces onto an air gap and the foil covering adds to the insulation value.The foil doesn't add value when the board is covered.For sticking in a roof, almost all of the boards were fine.

It faces in, it faces out, and it looks towards the space and the room.It should have foil on both sides because it can face the room, ceiling, roof and space all at the same time.

In an upside down installation, where the paper faces the unheated portion of the home, condensation from the humid inside air can get trapped in the insulation during the cold winter months.This will result in growth of mold and rot.