Window flashing tape

[Shawn Prentice]

Here is the problem-I installed some patio doors on an addition. The sheathing used around here is either polyiso foam or OSB with wrb. This particular addition has OSB with Tyvek. I understand that the wrb should lap over the drip cap that has been flashed with tape to the sheathing. But, I haven't found any flashing tape that sticks very well to OSB (it sticks to the wrb well), so for that reason I taped the top of the doors to the wrb. How concerned should I be about water getting behing the wrb? And if it is a concern, then what detail would you use to remedy the issue? Most everyone around here tapes to the wrb on all sides because it's easier than cutting back the wrb. I do it because I haven't been able to get the flashing tape to stick properly to the OSB and it seems like wasted effort if it'll leak anyway if water gets behind there. This addition will have vinyl siding. I've tried Protecto, Opti-flash, and MFN wraps with no success sticking to OSB. Thanks.

[Lavrans]

Re: Window flashing tape

I like to have drip cap made with a 3-4" up leg. You don't have to tape it then- the only reason for taping most drip cap is because it's made wrong with only 1 to 1 1/2" up leg, which doesn't create enough barrier. Even if you tape, the tape needs to be at least 3" or more. I don't use regular tape, I use 4"-6" Protecto Wrap or Grace Vycor and staple it at the top. It will stick very well to the flashing, and eventually to the substrate, but also can be stapled to add security.

[Shawn Prentice]

Re: Window flashing tape

The 4" are the types of tapes I am having a problem with (Protecto, Optiflash, MFN brand.) This job was a Marvin subcontract, so the drip cap supplied is what I am supposed to use (1-1/2" up leg.) What I did was to tape over the up leg to the Tyvek. The tape sticks well to the up leg and tyvek, but not the OSB. My question is whether I should be worried about water getting behind the wrb. And, if that is a valid concern, then what would be a solution if I can't get the tape to stick to the OSB in order to seal the top of the window/door under the wrb? If the tape won't stick to OSB well, then how does stapling it help?
I just did a job 4 weeks ago where there was a mix of foil foam and OSB. The tape stuck to the foam well, but the OSB not good at all. Areas where it was taped to the OSB were gone over multiple times over successive days without any real adhesion improvement.

[Dick Seibert]

Re: Window flashing tape

Most everyone around here tapes to the wrb on all sides because it's easier than cutting back the wrb.

Shawn:

Therein lies your problem, tape should never be used, it's my understanding that tape was designed as an air seal, the flashing should always be properly installed under and over the WRB, and then there is no need for tape.

[dgbldr]

Re: Window flashing tape

I haven't had any problem with Vycor sticking to the OSB we get around here, but Dick has a point. Flashing can be done just fine without adhesive tape. I see plenty of well done flashing jobs from the days before adhesive tape.

Another option is try a different brand OSB or go to ply.

[Shawn Prentice]

Re: Window flashing tape

I am talking about the 4" self-sealing adhesive membrane like Lavrans mentioned. The factory instructions say to 45 cut the wrb at the top corners of the unit, then run the tape up the sides over the wrb and under the folded back wrb at the top, then tape the up leg of the drip cap to the sheathing, then lay the cut back wrb over that, and finally tape over the wrb and 45 cuts. My problem is the flashing membrane tape I've used (brands listed above) doesn't stick to the osb sheathing very well, so I eliminated that step since it'll do no good. The only way the units can leak is if water gets behind the wrb. Is there anything that can be done to deal with that scenario, in light of the adhesion problem? Or, do I even need to worry about water getting behind the wrb?

[always-learning]

Re: Window flashing tape

Shawn,

I, as well as you, like to tape the drip to the sheathing. This makes it so that if water is running down the sheathing, behind the wrb, it runs over the top of the P&S and expels itself out over the top edge of the drip cap. OSB is more difficult to have it stick to, but if you really want it to, try using a heat gun after application to the OSB.

Heat the tape onto the osb and then use a rubber j-roller to push it into the graining of the OSB. Takes an extra step, but it usually sticks with no problem once it's been heated up slightly.

I'd follow Lavrans recommendation as I also use the vycor and protecto wrap for my installations. The heating of these tapes is much more likely in weather <60 Deg. Fahrenheit. The colder it is outside, the more heat will be required.

IMO, the protecto wrap sticks much better than the Vycor since they made some chemical changes to the Vycor, the beginning of this year.

[Shawn Prentice]

Re: Window flashing tape

dgbldr-I don't make the sheathing decisions. Also, around here, plywood rarely gets used. When I do this type of work I'm just a sub sent out to set doors and/or windows in someone else's project. They will pay for flashing tape, but not to have drip cap with a longer up leg on it bent up to match the unit or any others extras. I've started doing sill pans on installs that I contract, but I'll bet I'm one of few, if not the only one, in this area who does that. As far as working as a sub, no one will pay for those extras. I was even talking with a window salesman about sill pans a few weeks back and he said, "Can you say waste of money?" But, he's never repaired framing damage and I've done dozens of framing repairs from leaking windows. Another window salesman said he'd seen sill pans once around here about 20 years ago and not since. Where can I find a detail showing good flashing practice without using tape?

[Shawn Prentice]

Re: Window flashing tape

always-learning-do I have to use heat gun or would a hair dryer on high heat work? If not, is there a particular brand of heat gun that is better than others?

[always-learning]

Re: Window flashing tape

always-learning-do I need a heat gun or would a hair dryer on high heat work?

Heat gun..... Hair dryer won't work, unless it's from some of the women who grew up in the 1980's and listened to lots of Bon Jovi music. They had the super duper hair fryers that would have worked, but I hear that UL had them banned in the early 1990's ;-)

[Joe Adams]

Re: Window flashing tape

I'm pretty sure Protecto-Wrap recommends the use of a primer when attaching to OSB. It is a pressure activated adhesive so be sure to press it down with a laminate pressure roller.

[Shawn Prentice]

Re: Window flashing tape

Always-learning-Thanks, that's what I needed to know.

Dgbldr-I would still be interested if you could point me toward an old style flashing detail without tape.

Dick-the air sealing tape is what the framers used on all the windows (I was out there only to set what they didn't want to...3 monster patio doors.)

Deepcreek-thanks for the tip.


I've let the guy who contracted me know that I've got an answer to the adhesion problem and that I'm prepared to go back to fix the tops. The next problem is the all the windows are flashed the same way except with the air seal tape. So, if I go back to fix my door installs, then the framers will have to come back and fix all the windows. My hands are tied this time since I was a sub of a sub, so I must wait for the big boss to give the okay to stir this pot because everyone except for the guys I answer to will be pi$$ed.

[steves]

Re: Window flashing tape

As deepcreek said, get the primer for the grace P+S
We put some Vicor on with the primer then when we found out that the Goldguard system was not compatable and had to peel it off it was stuck so good that pieces of the sheathing riped off with it.

[dgbldr]

Re: Window flashing tape

Shawn,

I, as well as you, like to tape the drip to the sheathing. This makes it so that if water is running down the sheathing, behind the wrb, it runs over the top of the P&S and expels itself out over the top edge of the drip cap.

Yes, that's the generally accepted method and logic, but in reality it doesn't always work that way. The tapes we're talking about are of various thicknesses. When water runs down the sheathing, it's not going to climb the edge of 1/8" thick tape. It's going to run sideways on top of the edge until it finds an easier down path.

I have seen flashing done with foil tape of the HVAC kind and that's so thin I'm sure water climbs the edge. By the way, good foil tape will cling ferociously to OSB.

Anyway, the detail without any tape is to use L shape flashing with drip edge, copper or otherwise. Simply tuck the vertical leg behind the sheathing. Seen it on old and new buildings with and without any sealant. Works fine. Very similar to the Z channel you put (horizontally) between T1-11 sheets or similar. Works the same way.

[Shawn Prentice]

Re: Window flashing tape

Thanks dgbldr. Around here, the drip cap is usually in front of the sheathing, but it makes sense that it'll do no good if water is behind the siding. So, are you saying water climbing the edge of the tape is a good or bad thing? I know foil tape sticks well to osb, but it's not self-healing, as you know, like the thicker flashing tapes.

I did get a call back from the window guy I answer to. He talked to his boss and they agreed it should be fixed, but left it up to me. I said absolutely I would go out this weekend and fix the head flashing on the doors, but I didn't want to have to answer for the framers flashing details on all the windows. At least I'll know that the detail on the doors is right, which is what my boss and myself will be responsible for. Even though he provided the windows, the framers and GC are liable for that aspect of the install.