# Flashing a window with PVC trim



## Golfnut_NC

I am hanging insulated vinyl siding, D6, 1-1/4" projection. Two story house, about 33 sq of siding. I did J channel on my last house, and it was okay, but this one needs to be fancier, so I am going with PVC trim boards.
1-1/2 x 4" trim around the windows, 1-1/2 x 6 corner boards. I am cutting a 1-1/4" x 1" pocket for the siding to slide into, ala J channel. I am going to cement all joints, pocket screw, and use trim stick to help hide all joints.

The windows will be correctly flashed, starting at the sill and running the flashing over the nailing strip of the siding below, then flashing the sides, and finally flashing the header. Now to the question.

Over the window header I will have the siding sliding down inside the pocket, but how do I handle the rain that will run down the siding, into the J pocket I have created? Looking at the header trim from the side :

|| |_| <- siding
||___
||xxx| flashing | felt | sheathing
||xxx|
||xxx| <-- PVC trim board
||___|

The only thing I can think of is to use aluminum flashing and basically bend a J channel hidden inside the pocket of the PVC trim. It would start up behind the siding, come down to the bottom of the pocket, and then turn up along the inside face of the pvc pocket. I could leave a slight lip on the top of the PVC face so the aluminum flashing would be covered from above.
Even if I was to do all this, the best I have done is moved the water to the sides of the window, but I am still behind the siding, and just directing water down my window flashing on the sides.

Having to leave the expansion gaps for the vinyl siding in the PVC trim area leaves these exposures. What am I missing to control the rain? 

Gordo


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## Tom Struble

your never going to keep moisture from behind the siding

you flash horizontal surfaces out to the sides specifically so it can drain

windows and doors should not rely on ''trim'' for weather resistance


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## rossfingal

Here's a link to the "Vinyl Siding Institute's", installation guide.
http://www.vinylsiding.org/publications/VSI_2010_Installation_Manual.pdf
This may help.

Also, "Google" - "Rain Screen".

rossfingal

Happy Holidays!


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## Golfnut_NC

Thanks Tom. I realize I can't keep the water completely out, but it seems like my pvc trim is actually fighting me and acting like a funnel to put water right into my flashing. I understand some water would get back there anyway, but I will have all of the water that is cascading down the siding above the window, working its way right onto the flashing. 
Are you saying that if I have done the flashing correctly that it can handle all of that water?
Is there a better way of doing the trim work? I am thinking about cutting out a |_| pocket instead, so I would have a thin piece of pvc behind the siding . That would be a water tight way of forcing all of the water to the sides, where presumably at least some of the water would end up back on the face of the siding.


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## Golfnut_NC

rossfingal said:


> Here's a link to the "Vinyl Siding Institute's", installation guide.
> http://www.vinylsiding.org/publications/VSI_2010_Installation_Manual.pdf


Thanks rossfingal. 
This manual is much more comprehensive than the Certainteed manual I have been using. I noticed the use of the drip cap, under the J channel in the PDF. I had also noticed the drip cap in Tinner666's web site on window flashing http://www.albertsroofing.com/Window Flashing.htm. 
The windows do have brick molding on them now, and based on other things I am finding, I won't be surprised to find no flashing, or poorly done flashing (1981 construction so it should be there but.......). 
I was trying to decide if installing a drip cap between my pvc trim and the header flashing would be needed, to become the primary water diverter, thus allowing the flashing to be the secondary. I am concerned that the drip cap might look strange coming out between the window frame and the PVC trim, and I also wonder how much water would the drip cap even handle when the PVC trim is presumably nailed down tight over the drip cap.
I have an inclination I may be over thinking this..........


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## loneframer

Here's how I've done it in the past. It's important to remember to slit the felt and counterflash the J-flashing.


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## Gary in WA

You want to direct the water down over the window, not in to the side jambs, as you well know. Here are some of the best window sill, head flashing details I've found. After you read them, you will be dryer, inside and out. Take them for what they are worth, let me know what you don't agree with, thanks.

http://www.nrc-cnrc.gc.ca/eng/ibp/irc/ci/volume-11-n2-1.html
http://www.nrc-cnrc.gc.ca/eng/projects/irc/manage-rainwater.html
http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc50031.pdf

http://joneakes.com/jons-fixit-database/2062

http://www.cmhc-schl.gc.ca/en/inpr/bude/himu/codemo/codemo_090.cfm

And bad installs: http://media.godashboard.com/gti/1ResearchCap/1_3EnergyUtil/MoldResearch/Task3_3_200604WindowInstallationTest%20Report.pdf

Gary


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## Tom Struble

where as i can understand installing an end dam drip directly to the unit head i don't see how you could incorporate it into a J channel [manufactured or a component built J pocket

i don't see why directing to the sides and down and on to the drainage plane or out the drainage leg as Loneframer shows would present a problem with a properly SA flashed/wrb integrated flanged unit


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## Gary in WA

Good point, Tom. I was just giving the Op some window flashing (head and pan) ideas as he has head flashing over the brick-mold as he mentioned, #5. Directing down the side is fine, as long as it stays there. With water under wind pressure, it could veer off onto the paper and easily run under the side jamb channel flanges. (Unless a caulking bead was run under them before install). I mentioned this before in that Code site on window installs ... it covered fastener leakage in felt paper also (it gets saturated and hangs like a sponge on the building with every staple wicking (capillary) water to the OSB). Try to hide the top (hanging) staples under the next over-lapping course above. Any extra staples are potential leaks as felt gets more permeable as it gets wetter (5-30 perms). Add in all the nails for the siding, possibly thousands of holes that could be reduced to hundreds. OSB doesn’t like to get wet.
Looks like the helper installed the short siding with a gun nail out-of-slot……oops.

I fixed some siding and flashing similar to that pictured, though years older, just this year. The slots cut in the channel leaked water at the arch, though the siding was the older style with the water flange on the bottom that dumped the water from above right in to the arch. It filled it up and overflowed going in to a slot wetting the OSB which also needed replacement. We taped the slots closed with Grace as counter-flashing to prevent further problems. I’m surprised instructions don’t say that or do they? My “picture” reference was not to Loneframers’ pics. I’ll pull that now, thanks.

Gary


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## Tom Struble

thanks Gary:thumbup:,i agree we tend to put too many staples and other penetrations thru the paper which is why i now use a capped fastener for all wrb which not only helps to seal around the staple but also more securely holds the paper requiring fewer staples


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## Windows on Wash

Nice.

Tom...you should get that pneumatic cap stapler. The guys love it.


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## Tom Struble

i'm not that fast:laughing:

this model let's you select whether you want a cap or not,makes starting a little easier


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## Golfnut_NC

Thanks Gary and Tom for your posts. The links Gary posted were very interesting, although I admit I just skimmed the major documents and did not study them in depth, which is what I would need to do to fully comprehend the details. 
Since I am remodeling, and not removing the windows, all of my flashing will be outside of the RO. However, if I was understanding Gary's last link,

http://media.godashboard.com/gti/1R...sk3_3_200604WindowInstallationTest Report.pdf

it appears to me that spray foam, when applied correctly, was shown to be effective at keeping water out of the window opening. Did I interpret that data correctly?

I should have enough access to add spray foam to the RO / window first, then flash and WRB.

I bought a 50' roll of 10" pvc flashing to install on the jambs and header right before I put the pvc trim on the window. This is intended to be the primary water barrier, that will channel most of the water back to the siding surface. Under that will be my actual flashing and wrb. Probably overkill, but since this is not a job I need to make profit, if I waste a few hundred on over-flashing it is not devastating to me. As long as it is effective though. I'd hate to do all this and still not have an effective water barrier.


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## joecaption

Sell sticking wide window tape would work better.


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