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Community and Q&A

Outside corner flashing detail

kevinjm4 | Posted in General Questions on

i need help going around an outside corner w/ the flashing profile that I am using for my drip flashing that’s going around my house over the skirt/water table board. And I want to just use what’s on hand, I.e. splice them, intertwine, overlap whatever it’s called.

id rather not and can’t at this point in my project wait for a custom flashing that sits over the top of the ends and does the corner for me so to speak. I was hoping to get this aspect of the job done today.

Cant seem to find any details or videos out there doing an outside corner with my profile.
thanks for any help offered.

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  1. Expert Member


    I'll try and describe it as best I can.

    - Cut one end of the flashing along the seam which forms the junction between the two parts of the L the same distance as the flashing protrudes from the wall.
    - Bend the upright portion of the flashing so it creates a vertical leg that goes around the corner of the wall.
    - Bend the horizontal portion of the flashing from the corner at 45 degrees. The bend is only a slight one.
    - You now have your bottom piece completed.
    - Cut the flashing which will overlap from the other direction at 45 degrees. This cut should leave about 1/2" of the bottom drip edge intact beyond the 45 degree angle to be bent around the corner as a lap.
    - Install the bottom flashing.
    - Place a bead of caulking on the top of this flashing where it will be overlapped by the top one.
    - install the top flashing.

  2. Peter Yost | | #2

    Couple of considerations:

    1. It looks as though, using google images, that the more common relationship between cornerboards and water tables is to have the cornerboard terminate on the water table, rather than the other way around.

    I think it makes more sense to have just the opposite configuration: have the cornerboards extend to the bottom of the wall cladding system with the water table terminating at the cornerboard. This eliminates the water table 45 degree miter, notoriously difficult both in terms of keeping water out and appearance when the water table miter ultimately opens up over time.

    2. This gets a bit more complicated if the water table is two-piece, rather than one. With a two-piece water table detail, the cap accomplishes the slope to the top of the water table rather than the slope being accomplished by mitering the top of the one-piece water table.

    Given that the top or cap of the two-piece water table detail may extend well beyond either the vertical water table element and the cornerboards, could be that the vertical leg of the two-piece water table terminates against the side of the cornerboards while the top or cap gets notched around the cornerboards and does extend to meet the caps of each side of the corner.

    3. I don't understand why your water table flashing is at the plane of the furring strips; what function does it serve there? If both the water table and cornerboard detail, as they should, have the furring running behind them, then any flashing needs to carry back to the plane of the WRB.

    I don't think that I would flash the termination of the cladding on the water table detail at all; just let the plane of the un-interrupted WRB carry this load.


    1. Expert Member
      MALCOLM TAYLOR | | #3


      The rule of thumb for flashing walls with rain-screens is that the flashing at wall penetrations (including doors and windows) goes back to the WRB, but flashing between horizontal joints in the cladding only goes back to the furring, so that the cavity is continuous from foundation to roof. Both the photos Kevin and I posted show this. The water-table is covering a ventilation strip behind it. If the flashing went back to the WRB, how would you vent the cavity?

      According to our code, not flashing the horizontal joint between claddings is a violation.

    2. kevinjm4 | | #4


      There will be no miter in my water table corner joint. And there will be no slope cut into the top of my one piece water table trim, the flashing will accomplish what that would have, plus it’s hardie - that would be a nasty sloped rip cut.

      And The flashing is there also to keep the water table trim clean-ish. Note the profile, water should stay off the face of the trim for the most part.

      I could terminate the water table at the corner trim, that is an option, and just end dam the flashing at the corner board. It was a toss up for me and it’s been a while I can’t remember why I decided to wrap it all the way around, but I’m not at the point of no return either just yet.

  3. pnwbuilder | | #5

    I don't want to hijack this thread, but I am curious if your decision to install a water table was based purely on aesthetic reasons?

    1. Expert Member
      MALCOLM TAYLOR | | #6


      One of the practical benefits of including a water-table, especially one detailed as Kevin's is so that it can be easily replaced, is that it can be seen as a sacrificial part of the cladding, located in the area close to grade which has traditionally seen the most deterioration due to splash-back or snow accumulation.

      1. pnwbuilder | | #7

        Thanks Malcolm. Snow accumulation in our area is not a concern, but splash-back certainly is. Looks like I have to plan for more work in a few weeks :)

    2. kevinjm4 | | #8

      Another thing for me was that by using at least a 6” board down there allowed for me to stick to 8’ panels on my siding, instead of going with 9’. Practically it made sense for that reason as my wall from soffit to sill plate is about 100” at least on the roof overhang sides of the house. And also what Malcolm says is a great way of thinking as well. But ultimately yes they are optional.

  4. Colin63 | | #9

    Off topic but hopefully everyone who reads this will remember it. No matter what material used for flashing... Seal your overlaps with a quality silicone or I'll be there in 10 years fixing it!

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