Z-metal flashing on stacked windows
Fetch
| Posted in Energy Efficiency and Durability on
I have a wall of windows in the back of the house that is very exposed to wind driven rain off the ocean here in Washington state. My second window is now leaking which answers my question if these windows were flashed properly. I am going to remove all of the Hardie trim boards and use a liquid flash with the Tar paper WRB that was used. My question is, based on the photo, where is the appropriate place to use z-metal flashing? I can add it to the top trim pieces that are on the top windows but what about the long belly band in the middle that touches the bottom of one window and the top of another?
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Replies
bfetcho,
Treat every window independently. Each one should have a head-flashing with end dams. That flashing should be bedded in a bead of caulking on the top of the window frame, with the WRB lapped on top of the vertical leg.
https://hammerandhand.com/best-practices/manual/1-flashing/1-2-head-flashing/
Thank you for the quick response Malcom!!
Just to be clear, the flashing should be installed independently above each window, then trim piece above the flashing? See picture- are these correct locations for flashing?
When you say lapped over the vertical leg, you mean the top portion of the flashing correct? Just like the picture from H&H.
Thank you!
Bftetcho,
I was assuming that there are two layers: The siding, which covers the whole area except where there are windows, and a second layer of trim, which is the battens, the trim around the windows, and the belly-band. If that's the way it is built then yes what you have drawn is correct. The flashing over each window will go back to the tar paper and either get lapped by it or covered with liquid flashing.
If that belly-band is thicker and does not have siding behind it, you could use one continuous piece of head-flashing over all the lower windows.
And yes, the vertical leg is just the top part of the flashing like the H&H drawing.
If you have to take of all the siding, that wall would benefit a lot from a rain-screen cavity.
Hi Malcom,
Thank you so much for the quick response again! It looks like you were right in that there are two layers of siding. The trim sits on top of the hardie flat panels. In some areas the panels are cut so close to the window frame, it’s that tight. I cannot tell if the windows were flashed on the top and sides but I’m willing to bet that they are not. So, do I need to cut the siding to expose the window flange so that I can liquid flash the flange to the sheathing?
I agree that a rain screen would be ideal on this wall but what is the best way to fix this without taking all the siding off.
A lot of the trim pieces had moisture on the underside so moisture was making its way past the caulking.
Any ideas or suggestions would be helpful!
Thank you.
Bfletcho,
I can already see where the trouble may have come from. Wherever there is a horizontal joint between pieces of the siding panels there needs to be Z flashing, not just a bead of caulking. That is particularly important where there is horizontal trim over it, like that belly band which can direct water inward. Having used small pieces didn't help, and unfortunately that condition extends on each sides of the bank of windows.
If it were my house this is what I would do:
- Cut away the siding on all four sides of each window enough to expose the flanges and another 1 1/2".
- Install head flashing above each window.
- Install flashing tape, or liquid flashing.
- Fill the area of siding you removed with strips of Hardi-panel and caulk the joints between them and the existing siding, and the window frame.
Reinstall the belly band trim, and install z-trim where it spans in between the windows.
- To deal with the problematic horizontal joints and cover the repairs, trim the windows with Hardi-trim wide enough to span continuously between the windows. You will have to cut back the battens above the top windows to get it in there.
- Caulk all horizontal joints in the trim except those that have Z-flashing.
- re-caulk the horizontal joint on both sides of the window. That isn't ideal, but it's less susceptible to water getting in as the roof overhang above is closer there
I would look at the Hardie trim installation manual:
https://www.buildsite.com/pdf/jameshardie/HardieTrim-Boards-Installation-Instructions-1987326.pdf
The z should go above each horizontal trim piece and run all the way back to behind the WRB. This would mean cutting the Hardie panel a bit above where the exiting trim was and sliding the Z up behind the WRB, reinstall the cut out piece and put the trim back.
In case of the band between the windows, see if you can get a Z bent up with a long leg that can sit at the top of the lower window and run all the way up to under the flange of the upper one.
You don't want any horizontal trim directly dealing with water as you would need to rely on caulking to keep any water out from behind it. By putting the Z above the trim, it avoids any of this issue plus it can channel any water coming down behind the siding out past the trim/windows.
Thank you for your great responses! As advised by Malcom (I agree), I cut away some siding and found that water was getting behind the tar paper WRB so I cut some more to expose it. Definitely mold growing behind the WRB. It seems that I may need to change tactics because of this?
Should I cut more below the window in the picture? Wondering how much siding I should remove.
Thank you!
Bfletcho,
Unless the OSB is punky I think you are fine. You are removing the conditions in which mold can grow. I might coat the exposed areas with Concrobium to be sure, but once you are finished the mold should not re=appear.
Yeah, I do have one section between the two sliders that is soft and brittle (punky). Might be able to replace that piece without removing the sliders.
I’m thinking of trimming the widow out differently since it seems that large belly band was causing so many problems. The other problem was no head flashing on the top windows.I posted two options that would allow for flashing the top and bottom windows. The other option would be the belly band with metal flashing on top or top and bottom.
The trim was installed on top of the flat hardie board, is this the best way or would installing the trim straight to the sheathing (with WRB) be better?