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Flashing Duct Penetrations
Sealing the ducts to shed water also seals air leaks.
We have a number of duct penetrations through the exterior walls, specifically, 6-in. ERV intake and exhaust, 6-in. range exhaust and makeup air intake, and 4-in. dryer exhaust. For air-barrier continuity and water management, we sealed each duct to the Zip System sheathing using Zip Stretch tape.
We also taped the ducts to a piece of Zip sheathing we installed over the Roxul exterior insulation as a nailing base for siding around the ducts.
The Roxul insulation is cut away from a 4-in. area around the duct. The release sheet on a 4-in.-wide by 8-in.-long strip of Stretch tape is scored in about 1-1/2 in. from one edge so the paper can be removed in two pieces.
Here’s the sequence of the two-stage process:
One piece of release paper is removed, and the sheet is folded face-to-face.
The sticky side is bonded to the duct and pressed tight along the duct to the sheathing joint.After the tape is stuck to the duct, the other piece of release paper is removed and the tape is flared out onto the sheathing. Two pieces of tape are needed, and the second piece overlaps the first piece by about 2 to 3 in. at each end, so the seal is continuous around the duct.The Roxul insulation that was removed in order to install the flashing tape is reinstalled.Pieces of 5/8-in. sheathing are cut to fit around the duct. The sheathing pieces are in the same plane as the 1×3 furring strips and provide a nailing base for siding around the duct.Even though the duct is flashed at the wall-sheathing level, I install an additional layer of Stretch tape from the duct to the sheathing pieces for good measure. Since the duct is along the bottom of the wall, any water blocked by this layer of flashing tape will drain over the rain-screen vent strip.Double-flashed and ready for trim and siding.
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