R-Guard Installation Detail

Sealing Window Flange

metal studs with gypsum sheathing/OSB sheathing/plywood

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Install the window “plumb, level and square” into the rough opening prepared with Joint & Seam Filler and/or FastFlash.

Contractors option: if the manufacturer’s instructions say to “wet-set” the exterior window flange, install a continuous bead of AirDam, FastFlash or Joint & Seam filler on the back of the flange along the top (head) and sides (jambs) of the window -- making sure to leave the sill flange free of sealant for drainage capabilities.


Place the window in the prepared rough opening. Install fasteners as directed by the window manufacturer. Use AirDam as the interior air sealant to ensure compatibility with the treated rough opening and create a long-lasting, weather-tight seal.


Counter flash to the top (head) and sides (jambs) of the window. Do not seal the window bottom (sill) or obstruct weeps.


To seal the window flange, apply FastFlash over the outer edge of the window flange. Then, apply FastFlash over the structural wall adjacent to the window flange at the window head and jambs. Use a dry joint knife, trowel or chipper brush to spread the wet product to create a seamless membrane, directing bulk water away from the window and the rough opening. Apply additional FastFlash as needed to create an opaque, monolithic membrane free of voids or pinholes. Ensure both window flange jambs and the head-to-wall interfaces are covered. Do not seal the window bottom (sill) or obstruct weeps.

Ted Barnekoff - Air & Water Barriers, PROSOCO

Ted Barnekoff
Product Support - Air & Water Barriers


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