So, once you've built out the new walls, how do you deal with the large gap between those walls at the window and still retain the isolation? Here's what we did. A thin sheet of neoprene was used to cover the entire window sill from wall to wall so that it overed the gap between the walls. Then the window was trimmed out with 1X2 on the inside wall closest to the window and 1X3 on the outside. Rigid fiberglass wrapped in black fabric was placed between the trim pieces helping to separate the dual wall system. The sill trim stops just at the drywall. We over cut the neoprene so it can be wrapped around and covered with trim later. As the trim will be on the window plug, wrapping the neoprene around finishs off the drywall edge.

Once the window was trimmed out, we could start constructing the "plug".

			We started with a wood frame (we used 2X3's) made just small enough to fit within the window trim and used rigid fiberglass on all edges.

		What will be the back and the sides were covered with fabric.