Door and Window Detail

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French Door Flashing Detail - Rough Window and Door Opening


Flashing Tape

Flashing Tape to Back Edge of Rough Opening

  • Roll at the end with roller.
  • Corners have 12" long piece, folded around corner. Or use flashing corners
  • this example shows flashing tape over rough opening overlapping only about 1.5" of the front face

  • Go 6" up from sill pan [1]
  • Requirement is that flashing tape (self-sealing) extend beyond the window/opening flange. Since most flanges are under 2", that means 4" tape will do - to cover both window opening and to reach the house wrap. [2]

Flashing tape does not go to back of Rough Opening

  • Flashing tape vs flashing corners - flex tape is used in video below.
  • On sides of window (jamb) - tape is used on top of the nailing flange

Flashing Corners made from the Same Material

  • This is part-count reduction friendly, eliminating a specialized product and using multipurpose components for robustness, resilience, and antifragility.
  • This uses a chevron-like cutout for the corners.
  • The vertical part in this design is weak - the edge can break and let water in.

  • Note: the concept is to flash the sill, but under the nailing fin, not above. This allows water inside window to drain out the bottom. This is different than the jambs, where flashing is used above the nailing fin.

  • Note also that flashing goes UNDER house wrap at the top (header) part of the window.


  • MFM states that their cost is lower than butyl tape [3]
  • 400' of 9" wide tape are $138 [4]. 480 feet needed for SEH 2 seams - or $55.
  • Or 900' of 4" for $138 [5]
  • Compare to 4" butyl tape at 50 cents per foot - [6]. For the Seed Eco-Home 2 - there are 24 seams of 20' each - so $240 in flashing tape if using 4" - but really need to use 3" as battens are 3.5"