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Green Basics

Video: Air Barrier Inspection

Superinsulation Can't Work if the Windows Leak

Some of the hardest parts of a house to seal are the windows, which are really just big holes in a wall filled with glass, wood, and plastic. The reason it’s so difficult to seal around windows is that the hole spans many layers of different materials—drywall, framing, exterior sheathing, housewrap, and siding. In a superinsulated house, there are even more—the house featured in this video has an extra two layers of rigid foam on the outside. All of those layers need to connect to the window frame, which is usually made from a thin piece of wood, plastic, or metal. Because stopping air leaks is so important to energy efficiency and the durability of a house, it’s a good idea to double and triple check the air-sealing details at every seam of every layer in every wall.

Thick walls complicate window connections

Building Science Corporation designed the home in this video so that the drywall creates a continuous interior air barrier. The home’s 4-in.-thick layer of rigid foam sheathing puts the outboard-mounted windows several inches away from the interior edge of the wall. This deep gap around every window has to be bridged to make the airtight drywall work. BSC’s solution is a plywood box extending from the inside of the framing to the outer edge of the rigid foam, within each rough opening; everything from the foam to the framing gets caulked or taped to this plywood, making air sealing consistent and reliable. BSC principal Joe Lstiburek, Ph.D, P.Eng., ASHRAE Fellow, uses his eyes and experience to make a thorough inspection of the various sealants and tapes to be sure this detail works as planned.

Understand air barrier principles to solve real-world problems

Dr. Joe points out that in…


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