What you should know about spray foam insulation
Foreword by Ian Thompson, Editor
In this video post, Jordan delves into a comprehensive analysis of spray foam as an insulation and air sealing solution in new home building projects or renovations. Renowned for its high R-value and often high purchase and application cost, spray foam is typically hailed as an efficient insulator. However, as Jordan highlights, it’s not without its caveats, and its performance largely hinges on proper application.
Firstly, Jordan emphasizes that the desired insulation value can only be achieved if the spray foam is applied to the required thickness. An underfilled cavity (which can be hard to see), even if it meets the correct thickness, may lead to inferior insulation. Secondly, he addresses the issue of the foam potentially detaching from the studs, which can significantly impact its air sealing properties. This detachment can be influenced by various factors including the foam’s temperature, the condition of the studs, and the surrounding humidity during application.
For me I question the environmental and health issues associated with some spray foams. It can be messy to apply and involve a lot of clean up and waste if the applicators concentration wavers. Where I do like it to be considered is underneath suspended ground floor systems, especially when space is tight and sealing is difficult – it can stick well and can work better than other insulation options. Although he doesn’t explicitly discuss these topics in the video, it’s important to note that improper application of spray foam can lead to off-gassing, which is a health issue that we need to address more in our builds.
Jordan also brings to light some structural vulnerabilities of spray foam, particularly at the junctions where the wall meets the roof and the bottom plate of a wall. These areas are prone to air infiltration and require additional sealing solutions.
While spray foam can help meet building code requirements like all products it’s all about the skills of the applicator that makes this insulation product type win or lose. My choices for insulation are primarily about performance and cost, but the combination of sustainability and health rank a close second – and for me there may be slightly better choices.
In conclusion, the specifiers need to understand the importance of vigilance and knowledge when opting for spray foam insulation. Although a recommended product to consider for your home insulation I encourage clients to be aware of the potential problems and to ensure the correct application. Over to Jordan’s post.
3 Spray Foam Problems
Is Spray foam good enough for high performance air sealing?
Jordan takes a look at a few reasons why spray foam might not get you the air sealing performance you were hoping for.
There are five things that this wall behind me is doing right now. It’s keeping the roof off of my head, it is keeping out moisture, it is keeping out air, it is controlling heat, and it is controlling vapor drive. Today, I’m going to talk about this product here, spray foam, and its ability to keep out both heat and air. So, everybody knows that spray foam is a good insulator. It has a high R-value. If installed correctly, it can also be a good air barrier. There are a few things that you need to look for to make sure that both of those are done as well as they could be on a spray insulation job.
First, you want to make sure that your required thickness for your insulation value is actually there. The spray foam doesn’t have to be full cavity depth, meaning you don’t have to overfill the cavity and then come shave it back off. Especially if you’re using a thicker stud and your R-values are lower, maybe you only need, say, four inches of insulation and you’ve got a two by six. So, you’ll have some insulation that is just this bubbly texture on the front and it’s not shaved off. The problem with an underfilled cavity, even if it’s to the right thickness, is it’s hard to tell if there are any spots that are underfilled. If you went all the way to full cavity thickness and then shaved it, even though you’re wasting that time and that labor and the material that you’re putting on the floor, it’s easy to check to make sure that it is all uniform thickness. In this house, I’ve seen several places where it’s actually underfilled, where there’s not enough insulation, and we’re gonna have to come in and bring that back to full thickness.
The second thing that this spray foam insulation should do is keep air from infiltrating into the house. At least, that was the case in their original design. This is a house that we have taken over mid-construction. It was all the way to sheetrock, and they were putting cabinets on the wall. We’ve ripped off all the exterior cladding and all the interior and are redoing it, and we found several places where this spray foam is not only underfilled but also pulling away from the studs. And so, if that spray foam is pulling away from the studs in the same place that you have a seam in your sheathing and the exterior sheathing is not taped or doesn’t have a fully applied membrane of some sort keeping out the air, then your air will leak right through that hole in the gap in the sheathing and then right through the gap between your stud and your spray foam.
I called my spray foam buddy up, and I said, “Hey, what causes that? I’m doing this video. What causes it to pull away from the studs?” He said, “Man, it’s so hard to tell you in a quick phone call without actually being there because there are all kinds of parameters. There’s the heat of or the temperature of the spray foam as it’s coming out of the guns. Too hot, and you have a problem; too cold, and you have a problem. If the studs are wet, you’ll have a problem. If the humidity in the air is not exactly right and the operator is not cognizant of it, you can have a problem.” So, there are a ton of variables that the operator has to be aware of when he’s applying this to make sure that he is doing the best possible job.
Now, even if you get a really good operator and they put it in really well and your whole wall is airtight because you’ve done everything right, you still have this issue here at the bottom plate. Now, in this house, what they’ve done is they’ve come with this foam, this fire-rated foam, and have sealed the bottom plate. This stuff I don’t like for this very reason. I can come up here and chip it away all day long with my finger. Now, the idea is it goes in and then your finished floor goes in, and everything is good, and everybody’s happy. The reality is that we’ve got a lot more construction left here, and that is going to be chipped up all over the place. And then, over time, as this bottom plate expands and contracts and as our concrete expands and contracts at different rates, that interface is not going to hold up with that spray foam. It just doesn’t have the adhesion that we need. So, I much prefer either a caulking process or I’ll show you what we did here with the Poly Guard stuff once we get outside.
So, another place that spray foam is weak on air sealing is where the wall and the roof assemblies meet. I’m outside the original house right now. We’ve added this on, but it’s a great place to look up and see where the original rafters exited the house. We had an exterior wall coming up here meeting this roof, and they’ve put up OSB blocking, and then they sprayed it from the inside with spray foam for the air sealing. The problem is, every time that they have the scabbed-on stud tying the rafter into the load-supporting stud, there’s about a half-inch to quarter-inch air gap between every single one of those, and that’s a huge place for air to leak in. So, spray foam is prone to air leakage. What do you do? Well, we don’t depend on spray foam for our air sealing. We’ve done it in the past, and we’ve had good numbers that spray foam will give you numbers that hit code. We have to be at least three ACH here in Austin, down in Houston, they’re at five ACH. So, if you’re trying to hit those types of numbers, spray foam will get you where you’re going. But if you’re trying to get really low, let’s say passive, which is 0.6 ACH, then you’ve got to do a different strategy. I’m going to take you outside and show you what we’re doing on this house for both our moisture and our air control.
So, if spray foam is not the panacea of air sealing that we might have thought it was, what do we do? Well, in this case, we’re actually getting our air sealing from the outside of the wall with a luma. This is Polly Walls Illuma Flash, and it’s a fully adhered WRB that is stuck to our OSB and seals all of the seams in between the different panels. So, we don’t get air infiltration through there. Now, some different products that are applied with just say cap head staples will do okay on infiltration because they will get sucked in tight between those when the air’s leaking in between those seams. The fabric will get pulled in tight and will stop that air leak somewhat. But on exfiltration, you’ll actually create a balloon. You’re actually blowing that WRB away from your wall. So, I really like the fully adhered membranes for air sealing.
Now, remember, the wall coming down to the foundation is another very weak spot for air infiltration because on the inside, remember I said I didn’t like the spray foam between the bottom plate and the foundation? It chips away, and if that chips away, then air can just leak right through that seam. What we do is we use Blue Barrier’s Joint Filler, and this is actually an adhesive as well as a filler. So, it fills the gap, but it also sticks tenaciously to both the concrete and the bottom plate, preventing any air from coming up in there. We did that before we put on the Poly Wall Illuma Flash, and then we Illuma underneath that seam so any water that gets back here runs and is able to drain away on the foundation.
Thanks so much for watching. Comment below with your favorite air-sealing tips and tricks. Subscribe if we’ve earned it. Go follow us over at Instagram, and we’ll see you next time on the Build Show.
So, insulation works by keeping the air inside of it from being able to move back and forth. There’s a really good insulator, so I don’t know what the R-value of a foam cup is, but they just threw their McDonald’s cup, sorry, Chuckle Bell cup right in the wall and then thumbed over it, so I think it’s got a pretty good insulation value.
External Youtube related post: Everything You Need to Know About Spray Foam