Step 6: Seal the perimeter

Tom Silva installing a window «»
Cut a strip of 6-inch-wide waterproof membrane 1 foot longer than the window is wide. Center it under the window and adhere it to the wall so it covers the bottom nailing fin.

Cut two more strips of membrane 1 foot longer than the height of the window and repeat the above process on both sides of the window. Make sure each strip's lower end overlaps the strip under the unit.

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    Tools List

    • hammer
      20-ounce hammer
    • two-foot level
      2-foot and 4-foot levels
    • tacker hammer
      Hammer-tacker,
      for stapling builder's felt
    • utility knife
      Utility knife
    • 16-foot tape measure
      Measuring tape
    • caulk gun
      Caulk gun
    • drill
      Optional: Drill-driver and 1 5/8-inch stainless screws,
      for attaching sill extender to bottom of narrow aluminum sill

    Shopping List

    1. WINDOW

    2. CAULK

    3. MINIMIALLY-EXPANDING FOAM INSULATION

    4. 15-POUND BUILDER'S FELT

    an alternative to membrane for flashing the rough opening



    5. WATERPROOF MEMBRANE

    6. METAL FLASHING

    7. FOAM INSULATION

    8. 1 1/2-INCH ROOFING NAILS

    for fastening nailing fins to the sheathing