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Flashing Pipes, Framing, and Exhaust Vents in Exterior Walls

April 25, 2017
Read time: 2 mins

For walls with a pre-applied weather barrier, make sure the tape is compatible with the WRB coating—or use a primer

If you use wall sheathing with a pre-applied weather barrier (such as Zip System) or if you paint on the weather barrier then you may be at a bit of a loss on how to seal holes through the walls made ‘by others’ during the course of construction.

Because there is no house wrap to overlap, you need to rely on well-adhered flashing tape. Fortunately, there are a lot of great tapes to choose from.


Step by step:

  • The first thing to do with all wall sheathing is to tape the seams of the panels to keep air and water out.
  • Use a J-roller to make a solid the bond between the tape and the panel. Many of these tapes are pressure-sensitive, so you really need to mash them into the sheathing. 
  • The simplest way to flash an electrical box is to tape the bottom, the sides, and then the top—in that order. Other box-shaped holes should be flashed the same way: bottom, sides, and then top.
  • Framing than penetrates through a wall needs a saddle-flashing, and if you have some fancy stretch tape, the process is quick. Just flash the bottom of the framing to the wall, and then flash over the top. 
  • Again, it is important to apply enough pressure to activate the adhesive on the tape.
  • Sealing a pipe through a wall can be done with a single piece of stretchy tape, which is far easier and cheaper than flashing boots, which would then need to be flashed into the house wrap or taped to the wall sheathing anyway.

The rule of whoever cuts the hole has to seal it up can be made easier and more predictable if all of the subs know what you want and where to look for the flashing tape.


Some notes from David Joyce, a high performance custom builder and remodeler with a long track record of super efficient homes that do not rot:

"ZIP tape and ZIP sheathing work great together. For all other tape/sheathing combinations, use a primer. You can find spray-on primer in the roofing section of your lumber yard near the EPDM membrane."


—This animated sequence is based on a 3D model by ZIP System that we found in the SketchUp Warehouse. Technical assistance from David Joyce and Doug Horgan.


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