Warm air rises, so a considerable amount of heat is lost through leaks into the attic.
Here is a list of spots in the attic where air sealing is needed:

• Around the plumbing stack and any other pipes entering the attic. Since thermal expansion causes the plumbing stack to move up and down, the seal must be airtight yet allow for movement.

• Around wires or ceiling light fixtures that penetrate the attic floor. Electrical stores carry a putty-like sealant specifically for use on electrical wiring.

• Around ducting that enters the attic from inside the house – for example, from kitchen exhaust fans and bathroom vents.

• At the junction of the ceiling and interior wall partitions.

• At the top of interior and exterior walls.

• Around attic hatches.

• Around the chimney with a non-combustible firestop.

• Along the edge of shared walls.