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Advice for lack of rainscreen or proper flashing

I'm hoping to get some advice regarding my split entry house (circa 1990) in Eastern Canada that has no house wrap, tape or sealant of any kind. Wall assembly is (inside to out) 1/2" GWB, poly v.b., 2x6 studs, 5/8" OSB, 1/2" EPS rigid foam (nailed with roofing nails and no tape anywhere), vinyl siding (no furring). The brickmould for the windows and doors rest against the insulation and are only flashed at the top, tied back to the insulation, not the OSB. I've been replacing windows as needed over the last 5 years and have noticed damage to the OSB and under the windows at each location. Also found many rusted nails that fasten the rigid insulation. I was younger and "less knowledgeable" than I am now about flashing and drainage planes, so I simply replaced the windows/door in the same fashion as previously.

However, I have learned since then and so with the last window I replaced I framed the rough opening with ½” plywood to match the thickness of the insulation and used peel and stick flashing from inside the RO all the way around the frame to the OSB. I also flashed the window flange to the OSB after the window was secured. Then the insulation was cut back and butted against the plywood frame over the flashing. I’m fairly confident of my installation for this one window, but the others I’ve replaced and remaining original windows and doors are worrisome.

I will be replacing 3 windows and 1 door this summer and wonder if I really need to worry about the existing or older installations in terms of the impact on long term structural damage. Do you think it would be wise to invest in a whole house removal of the siding, rigid insulation and windows in order to properly install the house wrap/drainage plane, insulation (probably go with 2" rigid instead) and properly flash all windows and doors? Or do I simply repeat my flashing efforts during my remaining window/door replacements and hope that the existing OSB/rigid insulation plane will suffice for the long term?

Thanks in advance for your thoughts,
Darcy Grant

Asked by Darcy Grant
Posted Apr 5, 2012 12:27 PM ET


6 Answers

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If the original flashing methods on your house resulted in damage to the OSB under each window, you can be fairly confident that installation of replacement windows with the same faulty details will result in more OSB damage.

So, if you know you did it wrong, the right answer is: open up your wall again and do it right.

However, if that option is expensive and discouraging, you can always ignore the problem until the OSB rot is so noticeable that you have no choice but to fix it.

Answered by Martin Holladay
Posted Apr 6, 2012 7:42 AM ET


I agree, the proper course of action is to just fix ALL windows, which is daunting and discouraging for a DIY'r. However, if I were to replace all the windows and install the flashing as I noted in my original post, do you think this is the proper way to handle the window installations? And secondly, what do you think of leaving the wall construction as it is, without adding a proper rainscreen? Given that I'll be replacing multiple windows/door at once, this would the better time to invest in the whole house re-siding project.

Answered by Darcy Grant
Posted Apr 9, 2012 6:13 AM ET


I can't tell from your description whether your proposed flashing makes sense. To flash a window, you must first define the water-resistant barrier (WRB). I'm not sure what you are installing for a WRB -- is it the rigid foam? Or do you have a layer of housewrap?

Once you have defined your WRB, you need to flash your rough opening to drain to the WRB using sill flashing or peel-and-stick membrane. Ideally, your rough sill will be sloped and will include an interior dam.

Then you install your window, and you provide more flashing; in most cases, the perimeter of the window is also flashed to the WRB. All flashing should be lapped shingle-style. Ideally, there should be a drainage gap between the WRB and your siding, but such a gap isn't always possible. Even wrinkled housewrap provides some limited drainage.

Don't forget the metal Z-flashing at the head.

Answered by Martin Holladay
Posted Apr 9, 2012 8:25 AM ET


Hi Darcy, your problem is common here in Utah and I have remediated mold and rot from many homes just like you describe. The best strategy for me is to remove all the vinyl and label it as you remove (ie. nw 1a, nw 1b, nw 2 etc.). Undo the nails at the top flange and push the siding straight down until it unsnaps. Remove doors and windows, install a self draining housewrap, then flash as you re-install all windows and doors. This is a lot of work, but vital to the longevity and energy efficiency of your home.

Answered by bill bradbury
Posted Apr 9, 2012 8:54 AM ET


I guess that's my issue is that I haven't got a true WRB. The original builder didn't use housewrap or flashing (other than the z-flashing over the heads of windows and doors. So, I've flashed my window using the steps you suggested above to the OSB relying on the OSB as the WRB, but it was never really installed as a WRB.

Thanks Bill for your input. That's obviously the best way to approach this, isn't it? So, flashing the window to the OSB as a non-existent WRB is better than nothing, but not necessarily a long term solution. What has been your experience if I were to leave this wall construction as is? Do you ever deal with home insurance for remedy?

Answered by Darcy Grant
Posted Apr 9, 2012 9:01 AM ET


As you now apparently realize, OSB is not a WRB. If your flashing directs the water that sneaks past your siding to your OSB, your OSB will eventually rot.

Answered by Martin Holladay
Posted Apr 9, 2012 9:21 AM ET

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