Flashing 120-year-old windows to new ZIP R-sheathing
I am slowly retrofitting an 120 y/o home in climate zone 1. As typical with homes of this vintage it was very leaky, both of air and occasionally wind blown water during hurricanes. We had to remove most of the siding on one of the walls and are building it back with ZIP R-sheathing and rainscreen siding.
The question I have is how do I flash my old windows to the ZIP. The windows are still in great shape with zero rot and could probably last another 100 years if I can keep them dry. Do I pull off the exterior frame and flash behind? This would only serve to introduce water to the wall cavity correct?
This is the first time for the contractor to use the ZIP product so his crew does not have any experience with these situations.
Thanks in advance. I attached a picture below of the project in process. The windows in question are in the right hand corners of the photo.
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Replies
Mike,
On a job like this -- one that involves replacing exterior sheathing (or adding new sheathing on the exterior side of old sheathing) -- it would be best to come up with a window flashing plan before the work starts.
The best way to flash windows is to flash the rough opening so that any water reaching the rough opening is directed to the water-resistive barrier, or WRB. (In your case, the Zip sheathing may be your WRB, or perhaps you will be installing housewrap as a WRB.) Since the rough openings of older buildings lack flashing, the only way to do this properly is to remove each window, flash the rough opening, and reinstall the window. That isn't easy, but it is the best way to proceed.
A lot of builders compromise, and you can, too -- but you should do so with your eyes open. Caulk doesn't always work.
My usual advice on cutting corners is: whether you can get away with a flashing shortcut depends on the exposure of the house and how much rain you expect. In your case (a) the wall in the photo has a very short roof overhang, and that's not good, and (b) your original question includes the phrase "wind blown water during hurricanes."
My conclusion: your house is not a good candidate for cutting corners.
Martin,
Thanks for the answer. Here are a few more details and photos. The windows are set in an H-frame which seems to prevent a traditional new window pan and flashing as seen below.
My thought is to pull the exterior trim off and flash the ZIP to the H-frame, The H-frame just sits in the 2x4s, It seems to me either way sends the water in the same direction. At the top of the window, this would at least keep the water from running behind the window into the wall cavity. I'm not sure there is any benefit in pulling the windows all the way out.
The window sill is cut out of this H-frame, which makes it hard to put a modern/flashed sill in. I guess I could cut off the feet of the H-frame and then put in a modern/flashed sill but, I have no real world experience with this. Thanks for the insight. Its very hard to find good details about retrofits but I appreciate all the insight and experience on this website.
Mike,
I've never seen that type of H-frame before. Perhaps this system was invented to install windows in walls without any exterior sheathing -- but I'm just guessing.
With such unusual windows, I think you will have to devise your own flashing method to handle the details you encounter on site. Think like a raindrop, and use plenty of peel-and-stick. Good luck.