Continuous Insulation Using Styrofoam Over Tyvek (2025 Builders' Show)

In the ProTradeCraft LIVE Construction Demonstration Zone, we installed continuous exterior insulation using Styrofoam over Tyvek. The Tyvek was detailed as the water control layer so the Styrofoam could do its job of blanketing the house.

Remodeler Michael Anschel and editor Dan Morrison go through the "what" and the "why," while carpenters Swede Carlander and Nick Balkcum show the "how" part of the equation.

TRANSCRIPT:

We're going to talk about exterior foam insulation, and we're going to show you how to put it up. You know, the details are not really in nailing the foam to the wall. The details are in figuring out how to get everything watertight, airtight, and high-performance before throwing on an extra layer.

Bottom: Base flashing protects foam and pushes water away

That's right. So what we're going to do is put it on the wall here. We're going to do a detailed modified drip edge water table. It's going to project out an inch away from the house. It's going to be not quite a 90°—it's going to be a little more obtuse than that so it can shed water—then come down with a hemmed kick-out. And that's because water control is happening at the WRB; it's not happening at the face of the foam. So we want to make sure that the water that gets back behind the foam—because it's going to happen—is able to get back out of the system. But we also want to protect that bottom edge from UV and miscellaneous stuff.

DrainWrap allows drainage

We're going to put a sheet of Tyvek up now. A couple of things to note: we're using the drain wrap product; we're not using the flat wrap product. That's because we want that three-dimensional texture. You're all familiar with drain wrap, right? It allows for faster drainage behind the cladding because it provides a small space for water to exit. This is the most critical layer in the entire building assembly. This is where we control all of the water—we keep it from coming into the house.

Tyvek is the water control layer

The water control layer is an important detail. There are lots of thoughts on how to put a window in a wall or open a door. The method we're going to recommend is to cut the WRB flush with the framing. Now, the best—what he's doing right there, we're on it right now—the best way to do it is to cut the WRB about half an inch wider than the opening. But that's difficult to do; it's hard to hold a straight line. And the framing provides a good guide for the knife.

So we're going to go flush with the framing. After we tape the seams here, we're going to set a pan flashing in the window. We're going to use DuPont FlexWrap—I think most folks are probably familiar with the product. It's going to create our pan flashing. It'll go up the side of the window about six inches on either side and out onto the face. This is going to let water shed out and not behind the WRB on the sides.

We're going to get two pieces of tape and lap two inches onto the face of the WRB and two inches into the framing. This is going to create an air seal so we stop that air pathway from getting into the jamb opening.

Seal pipe penetrations with flexible flashing

Who seals their pipe penetrations? Anybody? Good—awesome. I wish all the hands went up, but I think we can all say we've seen job sites where there's a penetration, and siding shows up, and they just kind of side across it, right? This is another opportunity for air to travel along the side of the pipe and back into the house. So we're going to control two things in this move here.

Nick is going to demonstrate. We're going to apply a flashing to the bottom of the pipe. We're going to seal that flashing tape to the pipe itself—we're using the FlexWrap again—and then bring it back down onto the house wrap. It's a two-flashing process, again shingle-style, with a bottom element and a top element. But we are tight to the pipe, so we've air-sealed at the pipe itself.

I've seen this called a saddle flashing. Some other people call it other things. He sealed the bottom first before the top because, again, water's pretty good at following the law of gravity. And FlexWrap is really great at sealing around corners. I think the key detail there is that you seal it to the pipe, and then the house wrap makes it a heck of a lot easier.

Continuous insulation breaks thermal bridges 

So, we're going to put one inch of continuous insulation on the outside of the house. It's going to function as a thermal break. And really, in every climate zone, there's value in having a thermal break on the side of the house—whether you're in a cooling climate in the South or a heating climate in the North. One inch is kind of the minimum; that's where we should start. You can do more than that.

We're in Minneapolis in Zone 6, and farther north in Zone 7, we're going to put two, three, even four inches on the exterior of our structures. But at one inch, you're only going to make one of the trades a little bit upset.

Make change easy for the trade contractors to implement

Everything we've done to this point is exactly the same detail you'd use on any of your building projects. Period. There's no deviation. At one inch, most of your manufacturers have a detail that allows for standard nailing, a modified nailing pattern, or an elongated nail that lets you put up siding the same way you normally would. Other than corners, you're largely the same.

Most windows project out from the structure about an inch, so when you put your casing up, you've covered up the foam. You've got a little bit of that window left to nail to—just enough to butt up next to—and it looks pretty.