This video from Insulwise in Pittsburgh explains how to insulate an attic that is already insulated, as well as the importance of air sealing attics in the first place. There are three primary reasons to air seal an attic which are to reduce energy loss, improve comfort in the home, and reduce the flow of moisture (in the form of water vapor) from the home to the attic space so as to limit the risks for mold growth.

The main trick in locating air leaks that may be hidden beneath insulation is to first create a map of all of the air leaks in the attic floor before going up into the attic. These attic air leaks consist of wire holes, top plates, bathroom fans, drop ceilings and bulk heads, recessed lights, etc. Once the map is complete it is then MUCH easier for a team to go into the attic and methodically track down all of the penetrations in the attic floor.

00:00 Intro
00:13 What Are Air Leaks and Why are They Important?
01:20 Why Air Leaks are Usually Hidden?
02:15 How to Find Attic Air Leaks from the Rooms Below
04:00 How to Draw a Map of the Attic Air Leaks
04:54 How to Find Air Leaks and Seal Them
06:52 How to Seal Large Voids in Attic Floors
08:30 Finished View of Air Sealed Attic