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Vertical corner flashing & house wrap remains unclear on standard practice?

Ryan_SLC | Posted in General Questions on

Hey all,

I see details for metal flashing integration with house wraps for horizontal areas (like windows). So…what about vertical areas?

What about metal corner flashing at an inside corner? Is metal flashing saving the housewrap (so over the house wrap) or is metal flashing the last line of defense if house wrap fails (metal flashing is behind the house wrap)?

My plan for today is multiple layers of integrating a new osb wall to existing brick wall:
1. prosoco joint filler on most outside of trim area to seal air channels created by mortor,
2. Siga Fentrim 6″ shaped on brick wall and osb wall,
3. 4″ metal L mechanically nailed, then edges zip taped to Siga on both sides,
4. house wrap with appropriate taping vertical


More than needed, but anything specifically wrong?


Thank you!


Thank you!

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  1. Ryan_SLC | | #1

    So I see this question asked a lot without answer or that "half the country does it this way and other other half does it this way."

    I looked at the L flashing I bought at HD, the install specs are for horizontal, not vertical. But it shows the house wrap is....NEITHER in or out. It terminates completely before. That is 100% not where I've read.

    If we treat the roof underlayment as the house wrap, I suppose they are saying the flashing sits on top of the house wrap.


    1. freyr_design | | #5

      Counter flashing like this is used for future repairability. It allows for the removal of step flashing without removing your siding, people also use a two piece counter flashing in this area. You could just bring the wall underlayment down over the L or step flashing and have good waterproof, just harder repairability.

  2. Deleted | | #2


    1. freyr_design | | #3

      You may have just mislabeled and meant L flashing, as this build up with step flashing would essentially defeat its purpose?

      Also this layering would funnel water under underlayment.

      1. Deleted | | #8


  3. Ryan_SLC | | #4

    Hopefully what I did is safe.

    I did it as I said above to my two inside corners.

    Prosoco joint filler, Siga Fentrim 6" tape, 4x4" L flashing, and taped the OSB side to the wall with Zip tape--all shingle style.

    House wrap will go over.

    The corners are very much more defined now. Which is great. I hope I did it right, but I can't find vertical install wall transition I did my best.

    1. freyr_design | | #6

      I would not think of metal flashing as waterproof at all, I would think of serving the purpose of siding and shingles, a protective cover for the underlying water resistant barrier. Your build up seems fine.

      The problem with metal vertically is water is like a snake, it will find its way behind. It is overlaps that are the most important for water barriers (aside from zip, also with zip ensure that horizontal tape is applied first or you will likely get a leak as the tape bumps up when it crosses). The more continuous your wrb around corners, the better.

      For masonry, counter flashing is often used for horizontal transitions. This counter flashing often goes behind the masonry and ties into the WRB behind. Sometimes it is just a kerf the the WRB is let into. I would not use this approach on your system though as you do not have an overlap vertically.

      The point of step flashing is that if water gets onto the flashing and travels horizontally it will not just go under the shingles, it will be pushed out over the next row of shingles. If you had a solid piece of metal L flashing under the shingles if any water got on that and went under the shingles it would travel under the shingles until reaching your eave.

      Putting metal flashing behind a wrb makes little to no sense unless you are trying to support over a gap.

    2. Expert Member
      MALCOLM TAYLOR | | #7


      As freyr_design said, just as in your thread on outside corners, there is no useful purpose to using metal flashing on the vertical intersection of walls.

  4. Ryan_SLC | | #9

    Thanks all.

    It did support a straighter corner, so that was probably worth the 30 bucks it cost.

    So now that I firmed up the corner with the old brick to the osb new all, which I'm reading you all as saying did nothing for water proofing, should I put L flashing in front of the house wrap on inside corners?

    I did the Siga Fentrim at the very first level. I admit I wasn't as impressed with that $200 as other online seem to think of it.

    I will waste all the money in the world just to get it right. If you think leave it at house wrap now, great.

    Thank you!

  5. Ryan_SLC | | #10


    So I have read that caulking at my 4" trim from this inside brick corner to the new osb is considered the drain plain.

    It fails the idea of multiple protections, but I do have Prosoco filling the mortor gaps and Sig Fentrim in the corner on the brick and osb, plus the L flashing which is nailed and taped on....

    I don't like the idea of caulk being assumed as the successful drain plain because brick does soak up water, but the brick does not directly touch the OSB, so water isn't going to wick over to the OSB

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