Best Practices Manual

3.2 Window Retrofit
  • Existing conditions to be retrofitted.
Window Retrofit Detail Step 2 | Hammer & Hand
  • Carefully remove existing trim and try to salvage for use after new window is installed.
Window Retrofit Detail Step 3 | Hammer & Hand
  • Remove existing window.
  • Adjust framing as necessary to make opening square and allow for 1/2” of space around window frame.
  • If adding a sloped sill, be sure to account for the height of the sloped sill in addition to the 1/2” of space on each side of the window casing.
Window Retrofit Detail Step 4 | Hammer & Hand
  • Apply Joint & Seam Filler to corners, intersections, and edges of opening.
  • Tool into place.
Window Retrofit Detail Step 5 | Hammer & Hand
  • Apply FastFlash around inside of opening and extend out as far as possible from opening on face of sheathing.
Window Retrofit Detail Step 6 | Hammer & Hand
  • Lift up any existing building paper and continue FastFlash out as far as possible.
Window Retrofit Detail Step 7
  • When possible, bring FastFlash out over the top of siding for continuous lapping (shown with window installed).
Window Retrofit Detail Step 8
  • Use shims to leave a space between the bottom flange and building frame to allow drainage in case of window failure.
  • 1/16” to 1/8” horseshoe shims are recommended.
Window Retrofit Detail Step 9 | Hammer & Hand
  • Install window in RO and fasten per manufacturer specifications.
Window Retrofit Detail Step 10
  • Bead and tool Joint & Seam Filler along top window flange to prevent water intrusion.
  • Optional (pictured): Apply Joint & Seam Filler to jambs as well, but NEVER to sill.
Window Retrofit Detail Step 11 | Hammer & Hand
  • Install head flashing to protect the trim.
  • Complete the window retrofit by fitting trim and caulking around edges where the trim meets the siding on the sides, but NEVER the bottom.
  • Kerf bottom of sill trim with a 3/16” drip edge.


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