Replies

1. Expert Member
   MALCOLM TAYLOR | Oct 04, 2021 09:56pm | #1

   Forrest,

   If y0ur trim sits on the siding, the relationship of the furring strips to the R.O. doesn't matter much. If your siding butts up to the trim, you want the furring to straddle that intersection, either by using two pieces or a wider one.

   The new jambs should extend out to the furring strips if the trim is g0ing to butt up to the siding. If the trim is g0ing on top of the siding, the jamb extensions need to extend out to the front face of the siding. The 0nly time I could see the jambs just extending back to the sheathing would be if you were adding brick-stops to the windows.

   You may find this useful: https://hammerandhand.com/best-practices/manual/

   I'd urge you to consider a wider gap that 1/4". A gap that small is easily bridged by the wrinkles in the WRB, and difficult to screen off at the bott0m while still maintaining an opening. 1/2" works well.

2. 
   user-7601308 | Oct 06, 2021 02:19pm | #2

   ok! In my case I was going to have the siding but up to the trim, so I didn't have all the gaps from the clapboard siding profile if the trim sat on top of the siding.

   I do have some 1/2 inch cdx plywood I could use for the strips. It is just a little warped, so will take more fasteners to get it tight to the building.

   To clarify, I would put the strips right up to the sides of the RO and use either a wide strip, or 2 strips so I can put the trim on top, and have room to catch the siding which will butt up to it. Jambs will extend all of the way out to the depth of the furring strips. since my windows are not flanged, just wooden jambs, do I incorporate the window in any way to the housewrap, or just do the rough opening as well flashed and wrapped, and then have the trim flashed well to protect the window?

1. Expert Member
   MALCOLM TAYLOR | Oct 06, 2021 05:38pm | #3

   Forrest,

   Once the window and new jamb extensions are in:
   - Use flashing tape (something like Tyvek Straight-flash) to bridge the joint between the new jambs and the house-wrap on the sheathing. Run it several inches wide on the wall and out to the end of the jambs.

   Because the trim is in the same plane as the siding, the furring and head-flashing are done a bit differently:
   - The trim above the window should be furred 0ut on horizontal strips.
   - Above this a metal head-flashing with end dams gets installed onto the trim. It should be bedded in a bead of caulking on the top of the trim, and extend right back to the sheathing, with the house-wrap lapped over it.
   - Once that's done, the furring strips above the window get installed over the vertical leg of the head flashing.
   - The siding over the window is held up about 1/8" over the head-flashing to allow drainage.

3. 
   user-7601308 | Oct 06, 2021 05:58pm | #4

   thanks! my jambs are only 3/4 inch thick, so I don't have much to adhere to, but I will try. I guess, if I have room in my rough openings, I could add some more material to stick to? after running the flashing tape back to the sheathing, I would put my furring strips on top, and that pressure should keep it in place. better than nothing! and similarly, doing the head flashing prior to adding the furring strips.

   thank you!

4. 
   andy_ | Oct 07, 2021 11:31pm | #5

   Maybe I'm missing something here, but the standard and easiest way to do this is to butt the siding ends up to the trim. If your siding is going to be thicker than the window trim, just use a thicker trim.
   Putting the rain screen spacer material under the trim makes it unnecessarily complex IMO. The spacer isn't typically visually acceptable compared to the trim material and it probably isn't as weather resistant either. Even if you don't see the material, you need to now cover that gap at the window so another piece of flashing is needed. You also have to reconsider bulk water movement there too.

1. Expert Member
   MALCOLM TAYLOR | Oct 07, 2021 11:50pm | #6

   Andy,

   You may be right in this situation. There might not be much of advantage with wood windows.

   All the windows I use on rain-screens have been flanged ones. That makes it easy to fur out the trim, and not worry about protecting the strips as the window frame outboard of the nailing flange does that.

   The advantage is in extending the benefits of a rain-screen cavity to the vulnerable area around a window. I like to keep the furring strips off the flange on all sides. That creates a gap right around the window with all the important attributes a rain-screen adds: A capillary break, a path to remove bulk-water, redistributing moisture, etc.

5. 
   user-7601308 | Oct 30, 2021 01:57pm | #7

   Thanks for the advice thus far. I am getting even closer to getting them in, and wanted to share some pictures to see if I have the idea right. Excuse the floppy tyvek around the RO jamb, I haven't stapled it to the inside yet.

   photo A shows how my window frame jambs will be proud of the sheathing, and photo B shows the window jamb being flush with my 1/2 inch rain screen furring strip.

   Photo C shows that once I have the jamb in place at the proper depth, I will put some peel and stick flashing tape from the jamb over to the tyvek WRB I will do this on the sides, and head, but not on the bottom of the window.

   photo D shows what it would look like after flashing the jamb, and then attaching the furring strip.

   Since the jamb will be proud of the sheathing, the flashing tape will 'taper' back to the WRB. I guess essentially bulging out from the wrb. Especially on the head flashing, I feel like this will make a deviation to my otherwise flat drainage plane - but seems like the best way I can do this with the wooden windows I have.

   Siding will butt up to the trim.

   What do you think?

   Thanks!