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Flashing details for external door with rainscreen

canada_deck | Posted in General Questions on

There is real progress (floor and walls are up) on my energy efficient shed and now I’m trying to figure out details for installing and flashing a door.

My wall assembly is 1/4″ plywood on the inside, 2*6 studs, 3/8 sheathing plywood for a total thickness of 6 1/8″.  My door jamb is 6 5/8″ so it is 1/2″ thicker than the wall.
I will be putting Tyvek as the WRB over the exterior plywood, then 3/4″ furring strips and then HardiePlank siding.

I’m trying to figure out how to detail this assembly.

Here is what I have in mind:
Rough opening:
– Make a silpan out of flashing tape at the bottom.  Also run a piece of flashing tape down each side of the rough opening.
– At the top, I will run metal flashing from the wall and over the top of the trim.

Door:
– Install the door so that the door jamb is flush with the plywood surface on the inside of the shed (so the jamb will protrude 1/2″ beyond the exterior sheathing.
– Along the sides of the rough opening cut the Tyvek back 2″. When the door is in place, run some flashing tape that will cover the edge of the Tyvek, the 2″ of bare plywood and then make a 90 degree angle and run 1/4″ – 1/2″ along the exposed (perpendicular – outside) edge of the door jamb.  That becomes my WRB layer.
– Fill the gap between the door and rough opening with low expansion foam sprayed into the gap from the inside of the shed.  This foam will fill up to the flashing tape on the outside.

Trim:
– Nail a 1/2″ thick piece of wood (ideally PT but I will see what I can find) beside the door jamb.
– Install trim on top of that.  It will have to be thick enough to be slightly proud of the siding (which will be sitting on 3/4″ furring strips.)

One alternative may be to install the 1/2″ furring directly beside (in contact with) the jamb and then run the flashing over that.

Any thoughts on whether I am on the right track here?

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    Canada_Deck,

    It's a shame the door jamb wasn't sized to be flush with your inside surface and the outside of your rain-screen strips. That way you could just surround the RO with furring strips, and run another one so it covered the transition between the trim and cladding. As it is 1/4" shy, I would line the outside of the RO with 1/2" plywood wider by several inches than the trim.

    Don't plan on attaching the flashing tape to the door frame. Instead, run it back several inches into your RO before putting on the furring strips or 1/2" surround.

    Fasten the trim to your door frame before installing it (much as though it came with a brick-mold). You can either bed the trim in caulking, or caulk the backside of the intersection of the trim and frame. This both gives you a much more water-resistant joint, and makes hanging the door far easier, as it is held flush in the opening.

    Once the door is hung, push backer-rod into the gap leaving a 1" to 1 1/2" drainage space at the exterior, and fill the rest with low expansion foam.

    1. canada_deck | | #2

      Thanks for this Malcolm.
      Yes, if I was building a house, I would have been picky about the sizes. Because it is just a shed, I bought a door that was available at the local supply yard. It's a good high quality door ($600 CAD) but I didn't have a lot of choices since I wanted it to be 36" left handed outswing with no window and needed something on the shelf in a small town.

      Thanks for this recommendation. I want to make sure I have it right:

      On the plane of the wall working from the wall towards the door: My water barrier will be located on the face of the sheathing and will wrap into the RO. If any water sneaks underneath the 1/2 furring strips that surround the door, it will end up in between the edge of the RO and the door jamb and will then make its way down to the flexible sill pan.

      On the same plane but working from the face of the door towards the wall:
      The trim piece will be sealed with caulk against the face of the door jamb. That will act as the water barrier.

      Would you consider nailing the 1/2" strips directly to the plywood sheathing and then having the flashing tape go on top of them so that the water barrier would be on top of those strips directly adjacent to the door and it would be less likely for any water to ever reach the RO from the drainage plane on the wall? I could still put flashing tape along the inside of the RO in case anything got into there to protect that wood.

      I like your suggestion better than my original plan but I'd like to understand the specific reasons why.
      These seem like potential issues:
      - Getting a reliable seal between the flashing tape and door jamb may be hard - especially if it is just 1/4" to 1/2". As things move and contract, that might fail.
      - It creates a cavity in between the RO and the door jamb with vapour barriers on both sides.
      - Filling the gap entirely with foam will prevent any drainage.

      1. Expert Member
        MALCOLM TAYLOR | | #3

        CD,

        Yes you can use flashing tape over the 1/2" plywood or under. I don't think it makes much difference. Flashing tape on any of the surfaces of the RO or outside of the door frame would be good insurance, but certainly aren't essential.

        This video shows a similar approach - but he fills the whole cavity. https://www.youtube.com/watch?v=oXUfU5A5uzo

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