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Finally someone who understands flashing

jar546

jar546

CBO
Joined
Oct 16, 2009
Messages
12,996
Location
Not where I really want to be
IMAG0382.jpg
 
I found the stuff they sell at HD (I think) calls for 1" crown staples, or refers you to the manufacturers website which takes you to a site in China that sells tarps with no info whatsoever.....
 
This is pretty standard for what I see around here. Many of the window suppliers now have their own installation crews. they are very specific on how they want their windows set. Often I see flexible pan flashing from the installer. Idon't know if this is still the case with this building bust. What about drip cap? I can't tell if it is there in the picture.

Joe
 
I thought the window flashing tape was to be directly on the sheathing? I was told that any moisture that gets behind the house wrap will run down and follow in the top of the window. This info came from a class hosted by PHRC.

docgj
 
Doesn't really make much difference how you flash plastic wraps, water goes right through them anyway, DuPont was never able to pass the "Boat Test" with their Tyvek so they got an ICBO Report Approving it as an air-barrier, something not even required by code, eventually they got a test of their own approved called the "Hydrostatic Pressure Test" as an alternative to the "Boat Test", the Boat Test (ASTM D 779 and ASTM D 226) deals with how much bulk water can pass through it, the Hydrostatic Pressure test (AATCC Test Method 127) deals with how much water vapor can pass through it, and the surfactants present in redwood, cedar, and fibercement eat right through the plastic anyway. The stuff seems to have the uncanny ability to let water though then trap it once it gets into the walls.

If interested read Tom Butt, FAIA's excellent 2005 ASTM article.
 
docgj said:
I thought the window flashing tape was to be directly on the sheathing? I was told that any moisture that gets behind the house wrap will run down and follow in the top of the window. This info came from a class hosted by PHRC.docgj
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It is on the sheathing, at least at the top.

That installation is referred to as an A1. The flap that is cut in the WRB above the window allows the head flashing to be adhered directly to the sheathing.

Bill
 
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Hi Bootleg,

I looked at the portion of the upper window and I can see that the bottom wrap appears to be on the fin. What about the possibility that there's an an additional piece of flexible flashing under the nail fin as well as the one we can see. I know that some window manufacturer's don't like to see sealant used under the nailfins because they, mistakenly believe that because the bedding joint's depth can't be controlled the joint will fail. These manufacturers would prefer to see the self adhesive flashing reversed lapped on the bottom fin. I don't agree. AAMA's standards also speak to applying the bottom piece of flashing and sealing the bottom fin over it.

If that's the only piece of flexible flashing across the bottom, I agree with you because of the reverse lap.

Bill
 
My personal opinion is that if you place flashing over the bottom fin you are making an assumption that water will never enter behind the window.

If that is a safe assumption I don't know why you would bother with the sill pan.
 
TimNY said:
My personal opinion is that if you place flashing over the bottom fin you are making an assumption that water will never enter behind the window.If that is a safe assumption I don't know why you would bother with the sill pan.
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Hi Tim,

Sill pans are not typically required under windows with welded corners. Still there are ways to apply the tape similarly to what is depicted and still let the sill pan drain.

Bill
 
Again, my personal opinion. If I were doing it, I would do it differently.

Anderson depicts the flashing under the bottom flange, so if they added another piece over the top I don't think there is anything to prohibit it.

EDIT: I realize those aren't Anderson.. but I think we're all in agreement the flashing is required underneath the bottom flange.
 
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This is harder than it looks--from a code standpoint. Section R613 says to do according to the manufacturers written installation instructions. R703.8 gets specific gets specific about flashings extending to the WRB or exterior wall. If you are using foam with tape sealed joints for a WRB (code approved) most window manufacturers don't have instructions for how to do them (though the DOE Building America commissioned a good detail from the Building Science Corp). And then go get your Hardi Panel instructions, which the code also requires you to follow, and figure out how you are going to integrate them with what the window manufactuer says to do.

If you are very detailed you can do an excellent job with a pan in the bottom with a dam at the back of it, a separate head flashing at the top and don't double tape the fin at the bottom so that water can run out. Excellent detail can be done but you can't tie it to the manufacturers instructions or consequently the code. You have to use some judgement but I wouldn't pass the one in the picture.
 
Sorry to keep going on about Anderson.. but it's what we use here 80% of the time..

Anderson is very clear about "flash windows like depicted here OR follow the architects instructions". This allows you to use those good details. I am not familiar with the Hardi instructions.
 
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