Building Resilience (10): Open Cladding That Lasts

October 16, 2020

A cladding system designed to look great and leak like crazy

Last time on Building Resilience, we were flying around above the city of Minneapolis admiring what a great job we’re doing. 

On the ground, we were flashing holes in the wall, putting up an invisible WRB, and installing two types of rainscreen systems.

One, an entangled-matrix drainage mat is made from polypropylene and offers excellent drainage and compression resistance. 

It is being used wherever the ¾ inch PVC Paint Pro Panels from AZEK will be installed. The other rainscreen, Batten UV 
[Batten UV}
Is being used over the black InvisiWrap so that they disappear behind the open joint cladding system, also from AZEK.

MA: Here we have the intersection of our InvisiWrap UV and the ventilated rainscreen system, Slicker MAX, which then continues on around the house. On that portion of the house, the ZIP System is our WRB. and technically on the other section, 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. 
These battens, from Benjamin Obdyke—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.

The battens are stapled to the house, and we’re ready to do this open-joint cladding.

The cladding systems are separate, but intertwined to some extent. The panel edges are trimmed with architectural metal profiles, so a lot of the cladding layout is done when the trim is installed. The crew lays out the Tamlyn trim profiles to align with windows and other architectural elements. 

The Tamlyn profiles overlap the Paint Pro Panel edges to allow for movement, but the edges of the open cladding just butt the termination trims.

MA: This is a PVC deck board that we’re repurposing as a cladding material, which makes sense. It’s already designed to withstand the elements. It’s undersigned to be walked on, it’s designed to basically be beat up, and we’re putting it in a spot where it’s going to get a lot less weather, a lot less UV, it’s going to get no foot-traffic at all. It should last an incredibly long time. 
So we have three screws at the edges, which pins that piece in place. In the field, two screws keep it fastened to the structure. 
A lot of people have questions about expansion and contraction. And I learned a lot in this process. 
So, here’s some crazy stuff. We all know that PVC expands and contracts, right? Just like wood. Except that what I learned is that PVC doesn’t actually expand so much as it mostly contracts. 
And this is the crazy bit: after it’s contracted, it stops. So it goes through this process where it releases… how do I describe it? 
It’s like a piece of wood...

Let’s just cut this right here and go to the experts. Michael is summarizing a technical call we had with the Zoom team about sustainability, PVC, and cladding movement.
 
Dave Parker, AZEK: Yeah, so let’s talk about expansion and contraction because that’s what’s seen as the Achilles heel of PVC.
The trick is in installation. The installation plays a key role in limiting the amount of expansion and contraction that you’re going to see. 
The first thing to do is to fasten PVC correctly. Make sure you’ve got the right number of fasteners in it.
The second thing is… wherever you’re butting ends of PVC trim, glue those joints. It’s not the expansion and contraction that people have a problem with, it’s shrinkage. 
So how do you get around that? It doesn’t matter if it’s hot or cold outside, always install PVC tight.
When we see problems, it’s typically when people installed it in the wintertime, left gaps, it expanded out like it was supposed to that first summer, and then it got cold again, and that next winter, it never grew back out to its full length.
And they ended up with gaps. They went from  1/8 gaps in the winter to tight in the summer, now they’ve got ¼ inch gaps in the winter and an ⅛ inch in the summer.
You can constrain the expansion of the product, but you can’t stop the shrinkage of it. But you can constrain it. If you install it tight, and always glue your joints, now you’ve always got a full-length board in the summer and maybe a ⅛-inch gap in the winter. 
People don’t complain about a 1/8 -inch gap in the winter because they are typically inside their home. In the summer, when they’re outside, the board comes back. 
Deck boards do the same thing. So, we would always tell you to install the products tight.

Here’s how the open cladding sections go together. 

Over the existing sheathing the ZIP System R-12 panels provide continuous insulation and weather resistance.

At the base of the wall is a base flashing to kick water out and away from the foundation.
Because the joints in the cladding are open, the crew installs the black InvisiWrap WRB over the ZIP R-12.
Next, come the Battens and then the termination trims are installed as specified on the plans.
Open cladding pieces are installed according to a couple of patterns also specified on the plans. Spacer blocks are used to keep the gaps consistent and to speed installation.
The cladding is face screwed into the wall sheathing. The screw holes are plugged with Cortex plugs for an invisible look.
But invisible fasteners are not really very useful if the cladding system doesn’t work and you have to replace it. 
To that end, Michael got up early one weekend and broke out his scientific garden hose...

MA: Alright guys, I have here this very scientific tool

...and ran some experiments to test the open cladding hypothesis.

MA: It’s called a garden hose with a spray nozzle.
OK, hey. We are here on the site of the Building Resilience Show and I want to show you one of the finished sides of the house. We’ve got panels and soffit all on. We’ve also got our open-joint cladding system installed. The whole thing is finally coming together, and man does it look sharp. 
I wanted to show you how this open joint cladding system works. I think it’s new for some folks, and that’s totally cool, but for folks who know about it already, this is like an upgrade on the concept, in my opinion.
We’ve got InvisiWrap behind it, it’s a black surface, you can’t see anything. We’ve got the Batten UV system back there, from Benjamin Obdyke, so that all of the boards are held off of the black WRB by about ⅜ -inch.
And I’m going to show you how fast—I mean, I think this is pretty obvious, how fast it drains. 
Now the panel system, I can’t show you this side, because it’s all closed up.
But in the event of rain, if water got behind any part of this system, the entire thing could drain out the bottom. 
At the bottom of the wall is a ½ inch gap designed to let all of the water come flowing right back out.
I’m going to use my super-scientific hose, and I’m going to blast this surface with water. 
You can see that it’s dry down there right now, so this is the first run at this experiment (which isn’t really much of an experiment).
It’s training really hard. It’s like a sideways rain, it’s getting super-wet back there, but that’s OK because you know what’s happening on the other end? 
Let’s take a look, you see all the water draining out the bottom?
Not only in this system is the water able to drain out the bottom, but every few inches we have a full ½-inch gap that lets lots and lots of airflow back there behind the cladding system. 
We have excellent drainage, water cannot get hung up inside this system. The beauty of this particular system is that we’re using a PVC deck board. This is a TimberTech product from AZEK, we’re using it as a cladding system here because the problem with open-joint rainscreen is that the water remains on the leading edge of the board.
When we see this done with ipe and the like, the water just sits on that edge, and eventually —I don’t care what species of wood that board is—it’s gonna rot. 
It’s going to open up and that board is going to start to fall apart.
But with this product, because it’s made out of PVC, we’re just not worried about its ability to rot because, well because it can’t.

With a rot-proof open joint cladding system in place, we’re going to wrap this episode of Building Resilience and get ready for next week when we take a closer peek at the Paint Pro panels covering the rest of the house.

That includes below grade, as protection for the rigid foam insulation board.

Spoiler alert: There’s more unscientific science in that episode, too.

MA: What’s going to happen at the bottom of the wall?

Well, let’s take a look down here and see...
Until next time, stay tuned and stay resilient
 


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