Window wrap: what's best at the top?

[ThingOfBeauty]

What are folks using at the tops of window openings, before the unit is installed?
Most of the install instructions I've seen want great protection at the sill, decent protection at the sides, and then the window installed straight to the bare sheathing at the top, followed by flashings & tapes across the top that integrate into the WRB.
To me there are three different situations we treat differently:

1. on flanged windows, we attach directly to the bare sheathing. Since the WRB and so on lap onto the flange, seems to me no water would be likely to hit the sheathing under almost any circumstances. It would have to blow up 1-1/2" to get above the flange and we use a strip of peel-and-stick so it would have to get past the sticky seal. Then there's caulk between the flange and the sheathing anyway so you even have an extra bit of protection.

2. Brickmold units seem a bit more vulnerable. If there was already felt on the sheathing, water that snuck in between the brickmold & the head flashing couldn't directly hit the sheathing. But gravity would pull it down on the head of the window so I'm not sure the felt is doing that much good on a brickmold unit; we've started running a bead of sealant across the corner between the brickmold & bare sheathing before we put up head flashing.

3. A lot of times we install wood units that have no trim on them yet, we're attaching trim in the field. A couple of guys have taken to running aluminum trim coil or peel-and-stick down onto the face of the head jamb to a point that will just be covered by the trim we add later. I kind of like this idea, though I don't think we get great drainage off this flashing, especially after the painters come through a few times & caulk & recaulk, I don't see the harm either.

Well it's a head-scratcher; love to hear what others have decided.

[Riversong]

Re: Window wrap: what's best at the top?

What are folks using at the tops of window openings, before the unit is installed?

I think the jury's still out on the best window installation system.

The AAMA approves four methods:
A: sill flash, window, jamb & head flash, WRB
A1: WRB, sill flash, window, jamb & head flash
B: sill flash, jamb flash, window, head flash, WRB
B1: WRB, sill flash, jamb flash, window, head flash

In all cases, sealant is applied between window flange or trim and either sheathing or flashing, and between any overlayed flashing and window flange.

With brickmold or pre-cased units, either B option would apply.

In an article in the ASTM Journal, "The Importance of Integrating Flashing and the Water Resistive Barrier in the Exterior Wall Systems of Residential Buildings", a study performed at Oak Ridge found that self-adhering flashings applied directly to OSB caused deterioration of the OSB and eventual leakage, and that leakage occured with both types of self-adhering flashing (bitumen and butyl) where they lost adhesion to the plastic WRB at the diagonal cuts at the head - this did not occur with paper WRBs.

Though this is unrelated to windows, they also found that 1 or 2 layers of 60-min. paper kept pressurized water out better than plastic WRBs, were unaffected by surfactants like plastic WRBs, and were just as effective as an air barrier if seams were taped.

[David Meiland]

Re: Window wrap: what's best at the top?

One of the huge advantages (to me) of felt is the fact that I don't need that diagonal cut detail at the top of the window. We felt the wall up to the top of the window but leave off the piece that goes over the window. Ideally, the top of a course of felt aligns right with the top of the R.O. Install the window, tape the head flange to the wall, then install the next course of felt with a notch that's tight to the unit.

[monty1]

Re: Window wrap: what's best at the top?

1. on flanged windows, we attach directly to the bare sheathing. Since the WRB and so on lap onto the flange, seems to me no water would be likely to hit the sheathing under almost any circumstances. It would have to blow up 1-1/2" to get above the flange and we use a strip of peel-and-stick so it would have to get past the sticky seal. Then there's caulk between the flange and the sheathing anyway so you even have an extra bit of protection.

Hi Doug, I have a friend who does nothing but leaky condo repair, and everytime the peel and stick flashing is applied to the OSB by itself,it shows much more rot than if the flashing is applied to building paper first.
I think it is good practice to wrap the window opening with paper first then the other details.

[David Meiland]

Re: Window wrap: what's best at the top?

What about not using OSB?

[Lavrans]

Re: Window wrap: what's best at the top?

I think it would be a mistake to wrap the head- if water gets in, you don't want to trap it in the plywood.

The solution to the cuts at the top- for the systems that recommend the modified-Y cut- is simple: don't do it. Install a piece of WRB that runs fully across the head just above the flashing. No cuts to tape & then hope the tape holds its seal. That design is flawed from pretty much every angle, and is why paper WRB would perform better.

I flash above the trim- I think any water that gets down to the window frame is going to work its way to the sides, but not much through to the frame. I do caulk the flange to the sheathing, then run a layer of butyl over the flange, then install trim, then install z flashing, then bring paper over the top of flashing. If the window is a wood frame, I install the butyl 1/2" onto the wood, then the trim goes on top of that, but all other details are the same.

I don't trust the butyl to have a longer life than the window, but expect it should be effective even after it stops sticking. And it'll get replaced (hopefully) when the trim does fail & need to be replaced.

If it's OSB I'll wrap with the stapled flashings- I know some people prefer them (Vaproshield, Tyvek, etc.). They are cheaper, and if water gets behind them it can get out easier.

No OSB is good, too.

[Riversong]

Re: Window wrap: what's best at the top?

What about not using OSB?

What, you want to go back to the dark ages of plywood? Next thing, you'll be suggesting real wood sheathing. ;-)

[Dick Seibert]

Re: Window wrap: what's best at the top?

What about not using OSB?

This is off the topic of windows, but the APA just came out with some rules on OSB and roofing requiring that you ventilate your attic to use it, maybe they'll even come around and require you to ventilate your walls to use it; after all, Vancouver was requiring that even plywood on walls be ventilated with 2" holes, I thought Vancouver had such a good idea that I got permission from my SE to drill top and bottom holes in each 16" bay.

[David Meiland]

Re: Window wrap: what's best at the top?

What, you want to go back to the dark ages of plywood? Next thing, you'll be suggesting real wood sheathing. ;-)

Yeah, I was idly considering what it would take to build an all-local-lumber house here. The limiting factor would be the tempermental sawmill guys. I might actually just have to BUY a sawmill to git 'er done.

I've bought OSB once in my life. After a fire destroyed a garage some of us rebuilt it. There was a loft space above part of it for storage. There was no money to spend. I went and charged two sheets of OSB on the FD's lumberyard account, needing to save the $3 per sheet difference versus CDX. The chief was still pissed.

There were Volkswagen engine parts in that garage, which made for some very exciting moments during the fire.

[tayriver]

Re: Window wrap: what's best at the top?

We use sealant directly to sheathing at heads of both flanged and precased windows. This is in accordance with most recommendations I've seen. Although Tyvek recommends using StraightFlash VF for sealing the brickmold to sheathing, I don't use VF. I'm curious to see Bill R's technique for using VF!

I've used the modified "I" cut for WRB - but it's interesting that many seem to install WRB after window installation. Tyvek also allows this, so I might start doing this more often.

Also interesting is this from building science. "note no sealant behind flanges (unnecessary and dumb)". This is one of there more recent newsletters, and seems to contradict this earlier digest. Unless I'm missing something.

[Riversong]

Re: Window wrap: what's best at the top?

the APA just came out with some rules on OSB and roofing requiring that you ventilate your attic to use it

Actually, the APA document you linked to offers "guidelines" not requirements. Perhaps you were confusing the APA with Americans for Planetary Action or some such enviro-fascist group.

I thought Vancouver had such a good idea that I got permission from my SE to drill top and bottom holes in each 16" bay.

Is that to give the mice an entry and exit path? Kind of silly to use an impermeable sheathing and then put holes in it so it will breathe.

[Riversong]

Re: Window wrap: what's best at the top?

"note no sealant behind flanges (unnecessary and dumb)". This is one of there more recent newsletters, and seems to contradict this earlier digest.

I guess even good ole Joe can learn new tricks.

He also left out the building paper jamb wraps shown in the earlier article.

There is something to be said for the old "belts and suspenders" approach, though.

His current thinking, based on Canada's PERS system for commercial high-rises, seems to be that as long as there is a good drainage path, let the water leak. But he's relying a lot on the long-term adhesion of self-stick flashings.

[Lavrans]

Re: Window wrap: what's best at the top?

Also interesting is this from building science. "note no sealant behind flanges (unnecessary and dumb)". This is one of there more recent newsletters, and seems to contradict this earlier digest. Unless I'm missing something.

The one big problem with Joe L's point about this is that, while it's really not necessary (I agree with him on that) it's specifically detailed in most of the window manufacturer and WRB manufacturer's instructions. That means that, in the interest of attempting to guarantee that little warranty thing, I'll keep doing it until that's removed from their instructions or has been shown to be actually detrimental.

Sometimes you do dumb things because of good reasons. Sometimes not :-)

[monty1]

Re: Window wrap: what's best at the top?

[QUOTE=Dick I thought Vancouver had such a good idea that I got permission from my SE to drill top and bottom holes in each 16" bay.[/QUOTE]

Dick i am not sure if this is still a requirement now as rainscreen is mandated or not. Before they could make rainscreen part of the code, it was found that walls actually pulled in moisture and water due to pressure differences and those ventilation holes were a hope to minimize it. A lot of areas don't require them any more, but i am not sure of Vancouver.
You are right though, it is a good idea.

[Dick Seibert]

Re: Window wrap: what's best at the top?

Jesse:

As I've stated many times, I never use sealant, if the architect specifies it (like between concrete precast panels) I have it installed by a sealant contractor who provides a warranty complete with service schedule and offer of a maintenance contract to the owner, nobody knows how to properly size and install sealant beads, getting and calculating the coefficient of linear expansion of the diverse materials and installing the required backer rod and sealant bead is something only a professional sealant contractor knows how to do. Putting a sealant bead on something like a vinyl window flange and smashing it against a sheathed wall is stupid, even the sealant manufacturers all require sizing and backer rod to properly hold the gap to the proper size for the sealant to move the 9/16" that an 8' vinyl window moves in a 100° temperature spread throughout the year.

1) You can't water test your windows, sealants temporarily seal flashings if they are inadvertently improperly installed. All fenestrations should be water tested just like shower pans are required to be tested by code.

2) You can never completely waterproof a building, it's better to allow a building to drain when the water inevitably gets in than to try to keep it out. Our former Exterior Details moderator Patty McDaniel use to preach to us about never putting sealant on a horizontal bead.

3) Sealants, even the best of them, seldom last longer than 7 years on the weather side, if you are depending on sealant to waterproof your fenestrations you are guaranteed a leak before your latent defect warranty expires, you are doing your customer a disservice to install something that will only last 7 years.

4) The chemicals in sealants make some people sick, you are introducing chemicals like stoddard solvents and formaldehyde into homes.

5) Public perception that only bad contractors need to fill gaps in faulty construction with caulking.

As to Lavrans' comment about the manufacturers' warranties, they never honor them anyway, all they have to prove is that your bead wasn't properly sized or backed and they're off the hook. Do it right and you don't need it and won't have any problems requiring a warranty claim. It costs a fortune to retain an attorney to go after a warranty, they know that the manufacturers have armies of lawyers skilled at delaying until you run out of money with the reams of paperwork they throw at the case.

Lstiburek also says:

RR-0106: Problems with Housewraps
The primary function of a housewrap or building paper is rain penetration control. It is not air infiltration despite what the manufacturers say. The energy aspects of housewraps are vastly overstated. They have been embraced by builders for this function as can be evidenced by their market penetration. Yet their critical role in building durability is under appreciated and not marketed. It has been a triumph of marketing over physics.¹

Fortunately in our area plastic house wraps are not approved by code, you must use asphalt impregnated felt behind siding and two layer Grade D Kraft paper behind stucco, sometimes AHJ's will approve plastic as an alternative, but I understand the IRC does now allow it, why anyone would want to put a 10 minute boat test paper behind siding when it costs more than felt I'll never understand, Lstiburek says it's been a "triumph of marketing over physics", but it's hard to understand that contractors can be that gullible, especially as the failures mount.

¹ http://www.buildingscience.com/docum...ith-housewraps