All About Continuous Insulation (CI on Building Resilience 2024)

There is a balance between exterior continuous insulation and insulation between the studs

Transcript:

 Playing with foam adhesives again this week, I see.  Welcome back to Building Resilience, the show about whole-house solutions for extreme climate, healthy homes, and sustainability. This time, we're in Minneapolis during the coldest part of winter to install continuous insulation on a new addition.  

Michael Anschel: One of the cool things about an extreme climate construction show, like Building Resilience,  is the opportunity for extreme climate solutions, like continuous insulation.

Continuous exterior insulation included under an exposed floor

Continuous insulation includes under the floor if the structure's floor is open to below, like with this pier foundation.  The crew is making semi-SIPs, so to speak. A site-made insulated panel made from three-quarter inches of PVC and one inch of styrofoam held together with a subfloor adhesive.  The crew lays a full sheet of OSB across sawhorses to provide a flat and stable base.  Next is a sheet of PVC, and on that, they apply the adhesive.  The styrofoam is set on top, and they make another panel atop the previous one. This allows the panels to be squished together and the adhesive to set up.  When they're ready to install, They add adhesive to where the floor joists will be and slip the panel in place. 

Which is a lot easier said than done.  Ah, geez, here we go. The styrofoam sheets make a good base to rest on while installing, even if it eats up a little precious space.  Align the panel to the joists.

"How are you doing? " 

Hopefully, we will split the one on the far side. 

"We need to come my way a little bit. And push it into place."

"I'm good there."

"Really?"

"Yup."

"Alright, I'm happy then." 

The tricky part is screwing the panels into the framing when laying on your back with very little face room.  The outer edge of the semi-sip is sealed with flashing tape, and ideally, the tape is tucked behind the house ramp. 

How much continuous insulation on the walls?

Now that the underside is taken care of, we can put some styrofoam on the walls, cutting around the windows and doors. But how thick is thick enough? 

Now, you've seen us do continuous insulation before. Usually, we're putting two inches on the outside of the building. Now, there's this whole thing with ratios.

The amount of insulation you have outside the structural framing is equal to the amount you have in the wall cavity.  The more you have outside the framing, the less you need inside the framing.  

Best case, four inches on the outside, no insulation in the wall. 

The 2024 Energy Code gives Climate Zone 6 four options for walls.

At one extreme, we've got R-0 in the cavity and R-20 on the outside, or 4 inches of exterior foam.

The compromise is a 50-50 where you put 2 inches on the outside and 2 inches of spray polyurethane foam on the inside.

R-13  in the cavity, which can quickly be done with a 2x4 wall and R-10 outside.

And that also alleviates our need for any kind of a vapor retarder in the system because we've moved that condensation point out, away from the framing.

We've got a nice thermal break. It's good performance.  But more common is to put one inch of continuous insulation on the outside of your structure. That's what most builders are going to do. 

So that's R20 in the cavity and R5 outside. R20 is a fully packed 2x6 wall or 3 inches of closed cell foam.  The other extreme is no exterior insulation.

For that, you need to get R30 on the inside of the wall cavity. Which is about four and a half inches of close cell spray foam. 

And so we thought we'd give you a shot, uh, at seeing what that looks like and how we solve it.

So with one inch of insulation on the outside of the structure, we get a thermal break, but the rest of the wall assembly, we have to treat just like a typical wall assembly.

That means we still have requirements for vapor retarders, whether that be a smart membrane or two or more inches of spray polyurethane foam. Now, if you look at this structure here, we've got an existing house and we've got our addition. And we put the continuous insulation on the addition and the existing house.

Well, we weren't actually going to do anything with it. The client decided they wanted us to reside it. So we are and we've made some big improvements to it.

Thermal images show heat loss through walls

But when we take out our thermal camera,  we can see very quickly what a difference we've already made. So you can see at the bottom of the foundation where there's no insulation, we're leaking energy when we go up where all those penetrations are.

There's some insulation in there. But. It's still losing some energy, and when you move up one more layer to where we have our one inch of exterior foam, you can see that that surface has gotten very cold. And that's exactly what we want. We don't want to see all of that energy from the inside of the house leaking out into the world. 

So, some other things that we've done here. We've put a self adhered building wrap around the entire structure. So this is going to give us good air sealing, especially where we have all of those one by boards that were nailed up there in the early 1900s, lots of little air leaks all over the place.

The other thing is it's got these little nubs on it, and that's going to give us good drainage for any moisture that gets behind the cladding.  

Jobsite building science testing: drainage behind Styrofoam

Flashback sequence:
We have a condition, uh, this project. We've got an addition. We're going to be putting one inch of exterior foam on the outside. It's different for us. Uh, and on the house, uh, if we're not, we already have some HydroGap up on the house. And, um, while yes,  HydroGap is rated designed to stick to the face of XPS, and I could put the foam up on the structure and then the WRB over that, flash it, but something in my brain doesn't love it.

So, I spoke to the folks at Obdyke. They assured me that  The little nubs, these little nubs have enough compressive resistance that water will still drain behind the foam, which I kind of like. So, we're going to put it to the test here.  And, uh,  pour some water back there. And,  there's the stuff on the face, but the rest of the stuff that got behind there  There it is, it's coming out.

So,  I guess it works.  

<end flashback sequence...>

We've also added,  at the top of the foundation, a water table kick out flashing of sorts. So this is going to help Move any water just away from the structure that much more. It's a good way to make the building more resilient. 

The styrofoam goes up either vertically or horizontally, whichever works better, and is held in place with cap nails, which are generally ring shank for holding power in the sheathing. 

Again, the nubs on the HydroGap WRB provide enough space to allow drainage behind the foam. So the styrofoam is not the water control layer. The walls are watertight before the crew even thinks about styrofoam. The styrofoam is strictly a thermal control layer.  It's worth pointing out that there are two terminations at the exterior insulation here.

Two ways to terminate the bottom of the foam panels

The old house, and the new addition. Because the foundation sets proud of the wall framing, the crew adds a drip edge flashing to protect that joint.  Styrofoam is added to the outside, and the bottom of the foam is capped against bugs with a metal cap that extends back, but not far enough to close off that drainage gap.

If any water drips into the cap, it'll drip out the back. And that's one of the great things about using materials that are rated for ground contact. They can get a little wet now and then.  These mechanical penetrations are kind of another story.  The crew installed the styrofoam above them a while ago and they had to wait for the mechanical subs to extend them.

Yes, mechanical contractors can do math, they just left all the extensions long with the removable caps so that they can be cut to the proper length after the siding is installed.

Next Time: Windows installed from the INSIDE

And if you liked this episode, you're also going to like the one about Pella's new SteadySet windows, which are installed from the inside. 

Because they are SteadySet, they stay in the opening after you place them there. I mean, don't go off to the hamburger shop before securing them. Finish the job.  

Rarely have we come across an innovation that totally changes how we install the windows, and now we have not just one innovation, but six innovations on a single window that completely change how we install windows, which 

we're gonna do next time on building resilience.