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Building Resilience (9): A Redundant Water Management Strategy

Two WRBs and two rain screen systems accommodate two types of wall cladding
June 09, 2023

Last time on Building Resilience we were Installing Marvin’s high-density fiberglass frame windows and the stacking sliders both from their Modern collection.

The windows are fastened through the frame rather than through a fin, which makes it very easy to get the frames perfectly straight.

The huge sliding stacking glass doors were sort of the star of the show:

Michael Anschel, remodeler: The slider is a four-panel slider. Each of those panels weighs about 130 pounds. The track that it sits in is all unassembled when it arrives. So we get these super-long crates that are super cool, we turn them into work tables afterward, all designed to protect the components.

You lay them out on the ground and go through the construction manual, and you think, “Wow. This is going to take a few hours.”

And it does, but honestly, the frame that you’re working with is so lightweight, it is easy for two people to handle it, put it into position, make little adjustments, tack it into place…

You know, one of the cool things that Marvin has done with their instructions process is that they’ve added in QR codes. So, as you are installing the products, you can scan the QR code, and a little video pops up and shows you in context what you’re about to do.

Now that the windows are installed, they’re making hay. The drywall is up, and the painters are even inside painting the trim.

While he finishes up, we’re going to go outside for a peek at what we’re covering this week: Water management through WRBs and Rainscreen systems that provide vented claddings.

The primary WRB was the ZIP System sheathing on the outside of the R12 panels.

But because this house will feature an open-joint cladding system in some parts, Michael uses a black WRB from Benjamin Obdyke called InvisiWrap UV because it is designed to disappear behind open cladding systems and it has excellent resistance to ultraviolet light rays that break down mere mortal building materials.

The other cladding type on this house is a ¾-inch PVC panel from Azek. The AZEK sheets with PaintPro Technology will cover the Slicker MAX rain screen, and the open cladding will go over the black InvisiWrap UV.

"The house is almost fully wrapped now. All of the Zip Panels have pretty much vanished. You can see how we’re changing between the ventilated rainscreen and the InvisiWrap periodically throughout the house.

As the cladding types change, we’re changing our methodology. We’ve got batten strips that still need to go up on the InvisiWrap that will bring it out to the same plane as the Slicker MAX. Ultimately we’ll have a ⅜-inch air gap around the entire structure.

Under the section of the house with Slicker MAX, the Zip System R-12 panels are the WRB. On the other sections, the ZIP System is still the primary WRB, but because we are doing an open-joint cladding system, they use InvisiWrap UV which will give a beautiful shadow line behind the cladding system.

We also have this unusual flashing tape, which some people may be familiar with, but a lot are not.

It’s a fabric-looking material, and it’s slightly vapor-open. The invisiWrap UV is also vapor open, which is important in a cold climate. We want to make sure that we’re using the right product behind an open-joint cladding system, which is not going to be a typical WRB."

Before the InvisiWrap or Slicker MAX can go on, though, the primary WRB needs to be completely sealed off. Michael explains the flashing process on a couple of wall penetrations.

"I’d like to talk about pipe flashing. So here’s what we’ve got. One layer of ZIP tape goes inside the opening on the bottom and is seated all the way underneath.

The second layer of ZIP tape goes over the top of the pipe, like a hood or a shroud. It’s nicely protected, and this opening is really well-flashed. There’s foam back there inside, so it’s air sealed. And in case the water comes around and drips in here, we know it’s not going to get into the OSB; it’ll roll down the surface of the ZIP sheathing.

Sometimes HVAC guys cut oddly-shaped holes—like this one—that are larger than they need to be, and they don’t give you the opportunity to flash it first.

It’s the same concept, except on this one, we’ve added a third component. We have the seat, a side leg, and then the top.

They’re still lapped in the flashing order, and I think that’s going to stay nice and dry."

So with the windows and holes wall sealed up against leaks, we are ready to begin the rainscreen process. But first, we want to take a minute to answer what is sure to be a question.

Do you have to seal nail heads on ZIP System sheathing products?

No. The answer is no.

Fasteners that are deeply over-driven should be sealed with a piece of tape or liquid flash, but what you see here is overachieving, not following the installation guidelines.

OK, Let’s put up some InvisiWrap.

It comes in about a five-foot roll, so one worker can install it quite well by themself.

It’s installed with a slap stapler, not a cap stapler.

To place the battens, the crew snaps lines every 16 inches. They are not aiming for studs because there is two inches of foam between the cladding and the studs. Engineers from AZEK said it would be fine to screw into the ½-inch outer structural sheathing of the ZIP System R12 Panels.

"For an open-joint cladding system, it is really important that you keep the cladding from being held tight to the building paper. We want drainage back there because water is going to get in. So for that, we have these battens from Benjamin Obdyke.

They’re the Batten UV product; they’re a UV-stable black plastic because we don’t want to see the strip on the outside, so this will help keep it invisible.

You’ll notice it’s got all of these holes in it, and that allows air to pass horizontally through the system as well as vertically.

One of the problems with wood furring strips is that they’re solid. And if you’ve got a solid block running up to something like the bottom of a window, what happens is that the air is trapped. And if you forget to leave a gap at the top, it can’t get out.

Of course, in an open-joint cladding system, that’s not an issue because there are gaps everywhere.

If I were to be installing a lap siding, then the furring strips would create that condition.

I am in favor of using this entangled matrix system (Slicker MAX), which lets air flow in every direction, there’s really no way to cut it off, it runs behind everything, and you don’t have to monkey around with individual furring strips.

If you have to use furring strips, use these core-vented UV battens that allow air to move through the system up and down, and side to side. It reduces the chance of stopping the airflow, creating a bottleneck and not getting the ventilated rainscreen action that you’re looking for."

Battens are stapled to the wall to hold the cladding off the WRB. The staples are placed sideways to prevent compressing the battens

On the other parts of the house, SlickerMAX is installed similarly to how the InvisiWrap is installed. One small piece at a time, off a ladder, with a stapler.

It cuts just like any other roll product, fairly easily with a sharp knife.

"This is pretty cool. You can see here at this connection point, the Slicker Max is holding us off the house by about 3/8 -inch. And that’s really important.

What’s also important on the Slicker Max is the outer fabric, which helps keep the entangled matrix from compressing. A point load could compress it, but this fabric helps reduce that.

But when the siding or cladding material is pushing against it, it is very difficult to compress. It’s kind of like a snowshoe. When you step on a snowshoe, it keeps you on top of the snow because of its surface area, even though it has lots of holes in it.

It’s the same thing here. We don’t need a solid furring strip to hold our cladding off the building. We can have something with lots of holes in it that lets air flow behind it in all directions and still has the ability to resist that compressive strength when I go to put my cladding on."

Speaking of cladding, there are two types, and we’re going to talk about one of them next week: the Open-Joint Cladding system from AZEK.

We’re also going to do some weird science to see if this whole rainscreen system works.

Alright, guys, I have here a very scientific product called a hose with a spray nozzle., and I’m going to water the wall—in a way that it doesn’t… doesn’t. Isn’t. It’s never going to see water like this, but we’re going to make a point. I’m going to do my best to spray the wall and pan the camera at the same time…

Lots of water.

It is rushing out the bottom of the cavity. Crazy. I’m willing to bet that pretty much all of the water that we put into the wall, probably 95% is out already.

Until then, stay tuned and stay resilient.

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