Fibrous Insulation Deep Dive

The Build Show Podcast

Host Matt Risinger and builder Travis Brungardt conduct a deep dive into fibrous insulation, defining it as non-foam materials that trap air between fibers to create thermal resistance. They examine attic applications, emphasizing how

Key takeaways

• Fibrous insulation derives its R-value from trapped air between fibers, not the material itself, making air movement the primary enemy of performance.
• Risinger shares a personal attic installation failure where omitting soffit baffles caused wind washing that displaced blown-in fiberglass and exposed top plates.

Main topics

• Fibrous insulation definition and types
• Attic installation, baffles, and wind washing

Notable quotes

"Fibrous installations are any of the insulation products that are not foam based, but consist of a series of fibers that create air spaces between them."

Conclusion

The episode underscores that installation quality and air sealing are far more critical to fibrous

Transcript preview

Speaker 2 (0:00) Alright my friends, welcome back to another episode Speaker 1 (0:02) of... The Speaker 2 (0:04) Build Show podcast. That's right, my weekly time to get together with you and go deep. I got one of my favorite topics today. We're talking insulation. And guess who's with me in the studio? My buddy, Travis Brungard. Travis, thanks for joining me today. Speaker 1 (0:17) Man, thank you for coming in on a Saturday to be with me. This is a lot of fun. I'm super excited to talk to you about this. This is Speaker 2 (0:21) really fun. So we are talking specifically on this episode about... fibrous insulation, really any insulation that has some type of fiber related. We'll actually define that and talk about what that is. But this is a little bit of a companion piece or a little bit of a deep dive to Travis's series. Have you seen the Builder's Insulation Playbook series? Travis is doing an eight-part series. It's really more intended to be kind of a 101. Am I saying that right, Travis? Totally fair, Speaker 1 (0:48) yeah. Speaker 2 (0:49) rather than a super deep dive. And so we thought we'd do a couple of more deep dive episodes in this. But I would like for you to go back and watch this. Builder's Insulation Playbook. You can watch it on buildshownetwork.com. If you don't know Travis Brungardt, he's been with The Build Show now for... four or five years uh Speaker 1 (1:10) maybe four or five years Speaker 2 (1:11) something like that uh builder in kansas city one of the few builders i know who actually owns a trade license as well and not just one but two trade licenses uh so we got a lot to talk about today we're going to be going deep on fibrous insulation that being said from the austin texas build show studios let's get going Speaker 2 (1:35) Travis, thanks for joining me today in Austin. And thank you also for bringing me the fabulous iced cappuccino. I'm always Speaker 1 (1:42) on the coffee, man. I'm a giant coffee fan. And not only Speaker 2 (1:44) did he do that, but he brought me from Kansas City, a Broadway roasting company, signature espresso roast. Speaker 1 (1:51) I'm a real suck up, you know. You are a real suck up and that's what I Speaker 2 (1:54) like about you. Speaker 1 (1:57) No, man, I actually, I'm going to suck up a little bit more because we had just finished shooting the eighth. The eight part series, but it was insulation playbook. And then like the very next week after we wrapped your part one of your spray foam podcast dropped and it was a deep dive. Um, so much so that you had to have a part two. Yeah. Uh, I spent a lot Speaker 2 (2:17) of Speaker 1 (2:17) time on it, dude. Yeah. It was very well researched and prepared. And I was like, man, I'm envious because. While I was really excited to share that broad view of installation and maybe one-on-one is too far back. Like there's, there's a lot of good information in there. And I intended it as a reference that would lead builders, DIY folks, even trades people to understand the different properties of the installation so they could make a good choice. And I think we did that. In fact, you were on the last four episodes. I Speaker 2 (2:42) did Speaker 1 (2:42) feel like, man, I really wanted to go deeper on some of that stuff. when I heard part one and two of your spray foam series, I was like, we got to do that, but we got to cover the stuff you didn't get to yet. So I want to talk fibrous insulations with you today. Speaker 2 (2:56) I love it. And, and I'll be honest, this, um, topic is a good one, uh, for selfish reasons, because by the time this podcast goes out, people will know we have a brand new, um, AI for the build show. It's called ask.build. And it'd be as if you sat down with Travis and I were like, Hey, I got this question about insulation, about fibrous insulation. I'm thinking about using bats here and here. I'm in climate zone five. You know, are there any downsides to that? What should I do? What should I know? I was thinking about that or spray foam or whatever. And so when we film these podcasts, these days, since we started doing this, it's actually been in development for about I know, nine months or so, I've been thinking more and more of, hey, what would I want people to be able to dig up in our information database? Because Ask.Build is using all 7,500 of our videos and podcasts. Wow. That's Speaker 1 (3:52) a Speaker 2 (3:52) lot of resource. When you're on the Building Consensus podcast, when you and I are talking on the Build Show podcast, Prairie Sun and Timber that you did a couple years ago. Speaker 2 (4:03) This LLM, when someone asks that question, that stands for large language model, which is a dorky word for saying basically the computers watched every video. It's got all the information. It's got all the information. Does it use it correctly? Not 100 % of the time. We're still training it. But with that being said, let's jump into fibrous insulation. And I believe I'm stealing this from you. You want to answer the question, what, where, and why? So first off, what do you mean by fibrous insulation? Speaker 1 (4:30) So fibrous installations are any of the insulation products that are not foam based, but consist of a series of fibers that create air spaces between them. And that's really where the insulation value lies. And I think the most common one people are used to is the pink stuff, the good old fiberglass back and, you know, pink, white, yellow, whatever brand you prefer. fiberglass bats are just a network of literally glass fibers that are laid in a sort of randomized mat that creates a sort of a spongy pillow of air. Yeah. And if that fibrous insulation is touching all six sides of a stud cavity or a rafter bay, then it suspends the air. It limits the movement of that air and the air has the R value. Glass itself is not a particularly high R-value assembly, as we know from our windows, where we might get R1 or 2 or 3. It's really the airspace between the panes that gives you a good R-value on a window. So fibrous installations, in my view, are, for me, my rock wool. Your fiberglass bats, your blown product is also fibrous. So you can get blown rock wool, American rock wool. I think Steve shows a lot of stuff with that. That's right. And I know that you're doing some stuff with PowerWool now. Those are fibrous products, but I want to keep the board products separate. I want to do a separate episode with you. Speaker 2 (5:51) We're going to come back to sheet goods, basically. So Speaker 1 (5:54) let's just talk about bats and blown fiber. And when I think of fiberglass, I always think of attics first because that's where we send so much. And that's the reason that we see so much of it is it's cheap. It's so low labor to blow a volume of loose fill into a space. That it's one guy up there or gal up there crawling around with a hose and someone in the truck loading the Speaker 2 (6:19) hopper. Yeah. And if you haven't seen it before, it's basically a giant box truck that has like an auger, almost like a, think of like a blender or a grandma's Speaker 1 (6:29) KitchenAid on the counter. swinging around it's doing that it's breaking it up and pushing it through Speaker 2 (6:34) oh there you go pops the pellets into the auger for sure dumps Speaker 1 (6:38) them Speaker 2 (6:38) into the fire and so there's one person back at the box truck there's a giant white i think it's a four inch corrugated hose typically yeah i mean it looks like a big shop vac hose and a really really large uh fan it's blowing because it's got to blow this fairly heavy material But to your point, Travis, it's pretty quick. And funny story, I re-blew my own attic, I don't know, 15 years ago. Good for you, Speaker 1 (7:03) buddy. Speaker 2 (7:03) Maybe 20 years ago at my house that I was doing a remodel on. I wasn't smart about doing baffles, though, so that the wind washing wouldn't do it. And I remember my wife was in the driveway. I was up in the attic sweating my buns off, right? You know, it's Texas. Speaker 1 (7:18) This spring, it's like 120 Speaker 2 (7:20) in my attic. And I get done and I have this huge, probably 20-inch fluffy pillow. But I had not done the homework. I had not learned my building science at the time to realize that the soffits would get wind washing. And I went back up there a few months later expecting to see the same fluffy pillow. Speaker 1 (7:39) Big caverns with airflow. Huge Speaker 2 (7:41) caverns. Basically, all of my... top plates within and the first foot of drywall are exposed up there. Yeah, Speaker 1 (7:48) let's let's take that down to the entry level for people that don't understand when you talk about your wind washing, you're talking about you have ventilated soffit on that house. Speaker 2 (7:55) And so that's Speaker 1 (7:55) your Speaker 2 (7:55) air intake. Speaker 1 (7:57) So we've got stack effect pressure that and frankly, airflow, just wind itself Speaker 2 (8:02) that's Speaker 1 (8:03) going to push air into those soffit vents, which we want. That's what's going to keep the back of our roof cooler and drier. And then that air is going to exhaust. through a ridge vent or Dutch hats or whatever roof vent you like. You like little whirlybirds? Go ahead, whatever. But we're going to let the air in and let the air out. And so when you blew your insulation up against that top plate, which is where you want it. I mean, that is the weak point in the house, man. That top plate to ceiling connection. Ooh, that's the worst spot. So you want to insulate that well. But you mentioned a baffle. And what you're referring to is usually a foam or plastic tray that creates about an inch to an inch and Speaker 2 (8:35) a Speaker 1 (8:35) half space on the backside of that roof deck. so that the air from your soffit vent can still cool and dry the back of your roof deck without displacing that blown insulation. So omitting that step devalued the work that you did and hurt your building performance. Did you end up having to go back and fix it? Speaker 2 (8:55) I made a whole video about going back and doing baffles after the fact. Which I would have had to do anyways, frankly, because this was a remodel on a 70s house. But it was really not fun now that I had 20 inches of fluffy stuff in the way, whereas before I had, you know, four inches of fluffy stuff. And so like the origami of getting into all the spaces was awful. Yeah. Uh, and in fact, there was a pretty large portion that I had to pay a ninja to come in and, uh, and do it. There's, there's a guy in Austin, Texas, uh, named Quincy Bishop. Okay. Um, true R value, I want to say