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Wall outside corner flashing for air/weather: Tape seam, house wrap, metal L flashing too?

Ryan_SLC | Posted in General Questions on

So sorry for the basic question. A lot of googling focuses on the bottom z bar flashing drip/kick out. Hardie plank will be my cladding.

I understand the z bar at bottom, but what is the best wall outside corner flashing detail?

I am currently thinking;
-taping osb sheathing seams (zip 4″–doing all seams this way),
-4″ L metal flashing over tape,
-house wrap.

Is the L flashing right or superfluous? I’m thinking at worst, it’s not hurting anything right?

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  1. Expert Member


    The is no reason to add flashing at the corners. Flashing is used in two situations: To channel water from behind the cladding to the outside (head-flashing, etc.), or on the exterior surface to stop water getting behind the cladding or roofing (step-flashing, etc.). It isn't a supplemental WRB. In situations where you think for some reason the house-wrap might not be adequate, you use a flashing--tape or membrane.

    Why not use flashing at corners - or over the whole wall for that matter? First because it isn't a very effective barrier against infiltration when it gets holes through it, and more importantly it's not a good idea to add impermeable materials that can inhibit drying to the outside - especially when those materials, like metal, also can attract condensation.

  2. andy_ | | #2


  3. Ryan_SLC | | #3

    Thank you kindly to you both. I read mention of corner L flashing somewhere, but your advice lays it to rest.

    Thank you!

  4. Ryan_SLC | | #4

    My inside corner question received not a hit. Maybe I'll try here.

    My new osb sheathed wall abuts existing wall brick. I'm planning ISO cauling between mortar gaps, siga fentrim tape over the whole area, and then metal flashing--where the siga concrete tape is the true weather barrier but also isolating the galvanized steel L flashing from touching the brick.

    Bad idea or just right?

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