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Liquid Applied Flashing and Invisible WRB (Building Resilience Episode 7)

Hydroflash LA and Invisiwrap UV make a watertight, airtight, and UV-safe opening behind the open cladding
October 28, 2022

LAST TIME on building resilience, we were sticking house wrap to the walls. Literally. The HydroGap SA from Benjamin Obdyke is a self-adhering WRB, so it really helps to tighten the air barrier system.

Michael Anschel: Typically, when we have a paper or a non-woven fabric WRB and we get to the edge right here where the sheeting meets framing, we want to cut that and tape it so that we seal it so we get that air seal between our building paper and our framing.

With the HydroGap SA, it IS the tape. So we literally just get to the edge, cut it, bring it around, apply some pressure, and now we are fully air sealed at the framing so my sheeting, my framing, they’re all encapsulated. And I have no way for air to get behind my building paper across my sheathing to my window flanges.

This time, we’re going to take a walk-through window installation with a sticky flashing tape that disappears behind open joint cladding systems.

Oh hey Dan! Check it out. I wanted to show you the flashing tape on these windows. We’re using this hydroflash UV, it’s super awesome. Love this stuff.

We’re also gonna look into a tube at something magical.

In this tube, is something magical. In all seriousness, inside this tube we have some blue goo. We’re calling it the blue magic instead of black magic.

From our good friends at Benjamin Obdyke, this is a sausage gun. The stuff comes in these big floppy sausage-y type things. You stick them in the gun and then this is like a giant caulk gun that allows you to kick out a lot of volume very quickly.

What’s exciting about this stuff is it’s a siliconized polyurethane. So it stays flexible forever. It’s very very sticky when it comes out and it remains tacky for a very long time but it will always remain flexible.

And this is really really key when we talk about liquid flashings, or fluid-applied flashings, any of those materials that we want to cover gaps or cover spaces and be able to flex and move with the building, and have that long-term durability in our bulk water control areas.

PLAN OF ATTACK: Flashing a window opening for an open-cladding system

Our bulk water control areas basically boil down to holes in the walls, like doors, windows, wires, and ducts. The housewrap folds over the windowsill for an air seal. Over that, we’ll apply a liquid-applied flashing which will provide water protection and another layer to the air barrier system.

It covers the sill framing and extends up the sides of the rough openings too.

Because we’ll have an open cladding system on this house, we will cover all of the colors, but more importantly, we need to provide long-term UV protection. That’s where Invisiwrap UV and its corresponding flashing tapes come in.

The sill is already water and airtight, so the flashing tapes really just add UV protection to the flashing products and invisibility to the open cladding system.

So that’s the plan; now, let’s see how different the terrain is from the map.

JOBSITE KNOWHOW: How to Apply Hydroflash LA

To flash the window sill, begin with a couple of generous beads of Hydroflash LA. Lay a bead in the corner where the sill meets the trimmer stud, and go up the sides 4-6 inches.

Spread the Hydroflash with a squeegee to achieve a consistent 20-40 mil layer over the window sill. You can check the thickness with a thickness gauge.

With the rough openings flashed, it’s time to install the Invisiwrap UV. It’s not really invisible, though. Otherwise, how would the building inspector even verify that it is installed?

It is called Invisiwrap UV because behind the open joint cladding system, it disappears just like it should. It is also highly UV resistant, so it will not break down from exposure to sunlight.

Sol does his best to hide the ProtradeCraft logo when sharpening his pencil, but he can’t hide it forever.

There it is!

He uses the edge of his table as a cutting guide, which is pretty smart, and then he staples the WRB into place between the windows in the upper half of the house.

Following Sol and Steven is Michael, who is covering the liquid-applied flashing with a UV-resistant flashing tape, that’s part of the Invisiwrap UV system.

He begins by finding the center of the flashing tape and sticking it in the center of the window opening. For wide windows, use the buddy system. Extend each edge to the side jamb, tuck the tape tightly into the corner, and then stick it up the jamb.

Now we’re ready to remove the second release sheet and fold the tape into place.

Because it is not one of those fancy flexible tapes, you need to make relief cuts at the corners and then cover the corners with a patch. If you cut just shy of the actual corner, you can bend the edge of the tape over the vulnerable spot.

The jambs are then folded over the Invisiwrap and patched. The vulnerable point is triple protected here: the liquid-applied flashing, the flashing tape bent over the corner, and the patch.

Now it’s time to stick those windows in the walls.

Fortunately for these guys, they’re carrying one of the little ones, unlike this quadruple unit going into the kitchen.

Because it is such a big window, Sol uses a so-called laser to align all of the flex points to get a perfectly flat bottom. The guys outside nail the corners.

When they are happy that the window is square, the guys nail off the rest of the window. Steven is confident that he will not whack the expensive frame with his framing hammer but is secretly terrified that he will.

OK, here comes the part that may seem a little different.

When taping the flanges, he rolls the edge of the tape onto the actual window frame, bridging the frame over the flange to the HydroGap SA house wrap, which is sticking to the exterior sheathing.

If you just tape the flange, there is a gap around the entire perimeter of the window.

Of course, it slows the taping process a wee bit.

It is important with almost every kind of adhesive product to mash the adhesive into the substrate with a roller, squeegee, or a similar pressure-inducing tool.

At the head, they remove the backing paper from the sticky housewrap…

Wow, that’s a pretty sticky




and stick the HydroGap SA over the head flashing. Steven seals the angle cuts with a few dabs of the liquid applied flashing and squeegees it smooth.

Let’s look around and see what else we can seal with the smurftastic blue magic. Here we go—wire sticking out of a wall.

After calling Benjamin Obdyke’s technical department for affirmation that we can and should do this, we do this. Squirt a little goop around the wire and spread it out with a handy squeegee.

Looks like the easy road to a waterproof drainage plane comes in a sausage tube.

Next time we’ll start covering up these drainage planes with exterior cladding from AZEK.

All right, let’s talk about cladding. So we are using two primary types of cladding. PVC panels and PVC decking that’s wrapped in vinyl.

We already talked about the open cladding system we’ll use up high but down low; we’re going to do a board and batten detail using AZEK Sheets and trim with PaintPro Technology.

More on Window Flashing and Open Cladding

Building Resilience is a production of the SGC Horizon media network. See all of season two here.

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