If I may bend those ears listening about yet another window/waterproofing question. T111 siding has been used quite a bit here in California and I have seen that windows (usually aluminum) have been installed first, putting the plywood siding over their flanges. Evidence of water intrusion is not unusual on those walls more exposed to the elements. I’ve reversed the procedure before, embedding the window flanges (now vinyl) in caulk over the exterior siding followed with bituthane and trim.
I understand this installation method now puts the weak link at the head flashing, as opposed to what appeared to me to be at the bottom of the window before. Before I side my next job, I thought I’d put it out there to that great sea of wisdom to see if anybody has navigated these waters (literally) and found a better technique to installing vinyl windows and T111 siding.
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Replies
When you stack T1-11 you use Z flashing to prevent water intrusion at that joint.
Use the same technique over the window, just above the trim.
Yeah, we did that. Being a slow worker, I left the interior unfinished for many years, which allowed me to watch water leaking in over the flashing down onto the lower piece of T111. Not a lot of water, but enough to stain the lower piece. I believe that this would not be noticed if the interior were finished. So, who knows how well that Z0flashing really works.
You didn't by any chance paper the walls first, install the lower T1-11 sheet, then perch the Z-flash on top of that and then top it with the next sheet? And not lap the paper over the Z?
Any siding with vertical joints (that water could penetrate) such as t&g cedar, T-111, etc. should be flashed with dams at each end of the window head flashing to prevent any water that enters from traveling down the sides of the window behind the siding.
The siding should be held at least 1/4 inch above the flashing, and should be back primed and edge primed.
Rich