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Community and Q&A

Curved corner sill pan flashing

elyk22 | Posted in General Questions on


We have our sill flashing membrane spanning full width at bottom of rough opening (window sill -> interior 2×6 wall).

Some sill/jamb corners were not glued tight (curved up jamb) and there is air leakage coming through this created space.

How best to deal with this?

– Taping the leaky corner tight to inside 2×6 wall doesn’t seem right, and is tricky to get a good seal at that spot (outside corner/inside corner).

– Cutting a slice in the curved corner of membrane, starting about 2 inches from window -> back to interior.. would allow the curve to flatten out.. and I could air seal the leak closer to window with silicone, or other.

– Or should I could cut back the whole flashing membrane.. closer to window. A bit of work at this point.

I don’t believe spanning the full width of rough opening sill with the membrane was necessary . No water should ever make it past the window very far?

Thanks again,

The advice from the members of GBA has really helped my get through my project.

I owe you all a cyber beer!


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  1. Expert Member

    Cut the membrane flush with the interior of the window sill and lower jambs and seal the joint with either backer bead and caulking or canned foam. Extending the membrane the full width of the framing back into the conditioned space serves no purpose.

  2. elyk22 | | #2

    Thanks Malcolm,

    I understand it serves no purpose. I'll cut one back and see how easy it is to remove from plywood.

    Would it be worth it to leave a couple inches of membrane at window sill and fold to make backdam?

    If it does not come off easily from plywood.. is there harm having it full width?


  3. Expert Member

    No harm at all in leaving it. Whatever is easier. If you do cut it out you could leave a 1/2" proud to fold up as a back dam or cut flush and just seal the joint at the sill to prevent water moving inward.

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