More Product Guide
If you’ve seen any of the articles or videos about my basement renovation, you probably know I’m using a product called InSoFast to insulate the floors and walls. You can see it on part of the basement in the photo above. I’m not finished with the installation yet, but I’ve got enough experience with it now to be able to tell you about it.
The video below covers my reasons for choosing InSoFast. I’ve got at least two more videos on this product coming in the future: one on insulating walls with it and another on insulating floors. And in full disclosure, I should tell you they gave me a 15% discount on the panels I bought for “engineering review.” (I saved more money on the three appliances I bought at Home Depot’s Labor Day sale last weekend, though.)
Remodeling my basement
OK, let’s start at the beginning. If you’ve been reading this blog long enough, you know my wife and I bought this house in 2019. Since then, I’ve done a lot of work on it already (new heat pump, new heat pump water heater, faster hot water…). And this year it was finally time to do something about the horrid basement. Yes, I wrote a book down there, but the basement was a building science disaster area. Here’s a video about what I found after demolition in February of this year.
It was a mess. The walls were rotten, poorly framed, and uninsulated on the exterior. There was mold, asbestos, and high radon levels. The layout was depressing, as were the cabinets and other finishes.
In short, it was time to tackle this project.
InSoFast basics
The InSoFast panels aren’t just foam board. I’ve used that before (photo below), and yes, it gets you some insulation and air sealing and maybe water management. But you still have to figure out how to get drywall and subflooring over it.
The InSoFast system, in contrast, has built-in polypropylene studs. They make it easy to attach the panels to walls and floors, and they also make it easy to attach drywall or subflooring. And they eliminate or reduce thermal bridging, too!
In addition, they have channels on the back side, making them good drainage planes that you can integrate into an interior water management system. And they have horizontal and vertical raceways on the back side for running wiring.
These panels also have great strength. In the first video above, I talked about (and linked to) an InSoFast video where they hung 280 pounds of concrete blocks on one screw driven into an InSoFast wall stud. The floor panels are likewise strong and can easily hold a bathtub full of water.
Regarding the material, the foam used in the panels is expanded polystyrene (EPS). It has an R-value of about 4 per inch, so the 2-in. panels I’m using on the floor give me about R-8, and the 2.5-in. panels on the walls are R-10. Since I bought my panels, they’ve come out with a thicker panel (3.75″) that gets you about R-16.
The embodied—or upfront—carbon in EPS is about a third that of closed-cell spray foam and close to that of blown fiberglass.
Basement building science
Basements need all the building science you can throw at them. They’re connected to the ground, which is good for helping to keep cool in summer. But that connection also means controlling water is critical. It can come through the walls and floors if they’re not watertight. And what 1961 house is watertight!?
So, we need insulation, yes, but we also need a good air barrier. That’s not only to help with heating and cooling but also to keep soil gases like radon, water vapor, and methane out of the house.
The heat control layer is the insulation in the InSoFast panel. That’s where most people start their thinking, but in terms of the building science needs, it’s the least important.
Options for insulating basements
When insulating a basement, you have some choices.
- Fiberglass blanket on walls—I’ve seen them in Atlanta basements, but they’re more common in colder climates. You still have to figure out how to cover them with something if you want to finish the basement.
- Framed 2×4 wall with fiberglass batt insulation—This is probably the most common way they’re done. Sometimes the builder puts plastic sheeting on the wall in an uninformed attempt to control moisture. This method typically has a lot of problems.
- Closed-cell spray foam—High upfront carbon, but it does insulate, air seal, and control moisture. You still have to do something to cover it if you want a finished basement.
- Rigid foam board—This is what I talked about in the InSoFast basics section above.
I didn’t mention exterior insulation, but that’s more a possibility for new construction. There is a method for putting closed-cell spray foam on the exterior of existing homes without having to dig up everything, though.
Why I chose InSoFast
From what I’ve written above, you no doubt know my reasons by now. But let me summarize them here:
- InSoFast handles all the building science needs of controlling heat, air, and moisture.
- The built-in studs make attaching the panels to walls and floors easy. They also make it easy to attach drywall or subflooring on the other side.
- The built-in wiring chases make doing the electrical work easy.
- They’re very strong!
The InSoFast system is cleverly designed and easy to install. I’ve been very happy with my choice.
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Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can follow Allison on LinkedIn and subscribe to Energy Vanguard’s weekly newsletter and YouTube channel. Photos courtesy of author.
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14 Comments
Can you explain the drainage plane between the InSoFast sheeting and the plastic sheeting on the walls from the interior drain replacement? From the pictures it looks like the plastic only goes up 6 or so inches from the floor. Wouldn't any water come down the panel and then pool between the panel and the plastic?
armynavy17: Good question. Yes, it shows that I left the interior perimeter drain plastic up the wall a few inches, but I quickly changed my approach there. I ended up cutting it all the way down to the slab. That was partly for the reason you mention (water pooling between InSoFast panel and plastic) and partly to get the panels to lie flat against the wall.
If I'd left the 6 inches of plastic, however, I don't think there would have been much of a problem. There was a little bit of an unsealed gap in front of the plastic, too, so water coming down there would find its way to the drain below.
A concrete block wall seems like an ideal application surface. I wonder how well the product would adhere to a poured concrete foundation wall, which tend to have lots of bumps and protrusions (e.g., broken-off tie straps, vertical seams every couple of feet where forms were joined) above the plane of the wall.
I spent a great deal of time with lots of rub bricks trying to clean up those areas when I applied XPS panels to my interior foundation walls, eventually opting to use both adhesive as well as mechanical fasteners (Trufast plastic tree clips).
My basement is a poured wall. I knocked down egregious protrusions with a hammer (mostly along seams). The adhesive applied to the polyethylene holds the panel off the wall slightly so smaller protrusions aren't an issue. There were areas where the wall bowed in a little bit and I followed InSoFasts advice and just applied more glue to the back of the studs in those areas so that the panel was held off the wall more. There were maybe two areas where the wall bowed out (imagine a soccer ball embedded in the wall but sticking out maybe half an inch) and for those areas had to shave out a little divet in the back of the EPS so the panel would lock together with the other panels. With the way the panels lock together you end up with a nice flat wall even if the concrete underneath isn't perfectly smooth.
jadziedzic: My CMU walls weren't perfectly flat and smooth either, nor was my slab. It's not a problem, though, because as Ryan52403 said, you can cut out some of the InSoFast panel on the back side to get it to go on properly. That's really easy to do where the bump goes up against foam. It takes a bit more effort to do so if the bump hits a polypropylene stud, but it's still doable.
In the photo here you can see Jon Porter helping me install a panel over the part of the wall where we had to install angle iron above the window opening. Look closely and you can see we carved out part of the backside of the panel in that area. I think we used an oscillating multi-tool to make that cut but I later found my table saw to do a better job with that kind of cut.
Their website has a pic of a before and after over what looks like a field stone foundation. Is this actually a good solution for that? It seems like you’d want at the least the interior drain, for sure. But would it work with the right detailing?
I have a small area of the basement I’m considering trying it on.
ianb: Yeah, I think it would be difficult to put InSoFast panels over a rough field stone foundation. You need a nice flat surface if you want to glue the panels.
Great video! When it comes to building something proper and ensuring everything is done right, I usually rely on groundworks customer service https://www.pissedconsumer.com/company/groundworks/customer-service.html and their team. They’ve always been super helpful and knowledgeable, making the whole process smoother and more efficient. Whether it’s advice or hands-on expertise, they’re the ones I trust to get the job done properly
Allison, I wish you were a couple steps ahead of me instead of a couple steps behind me.
I just put up some InSoFast in my basement. They say the seams are self-sealing but after putting it up, I can clearly see that there are gaps, particularly at the corners where the panels come together. It looks like you're using a low expansion spray foam to seal the seams as you place each panel. It's too late for me to do that, any suggestions for how I could seal the seams once InSoFast is already up? I was thinking about just using latex caulk applied into all the corners where the panels meet and then covering the seams along the edges for good measure.
Along the bottom edge where the EPS and the concrete slab meet I was going to use Silicone caulk for additional moisture resistance.
Do you think that would work? Any suggestions to improve upon that?
Ryan52403: You got your wish. I'm actually ahead of you because I wrote this article three months ago. We got drywall a month ago and are doing cabinets now.
Yeah, I used one-part gun foam at the seams as I was assembling the panels, but I missed some and had to go back and spray the joints after assembly. You also could use caulk or air sealing tapes. But as you've noticed, their advice about not needing to add sealant to those seams doesn't work out in real world projects.
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I would go with tape rather than caulk. I've been using Siga tapes on my build and I am very impressed. For interior work they recommend Rissan tape and i've found it sticks well to everything but is just un-sticky enough that you can generally pull it off and move it if you're quick enough. After you press it flat and leave it for a day or so, it's not coming off. My insulation contractors have been using Tescon Vana and that also seems like a great product. The point of the tape is that it is way more flexible and sticky than pretty much any caulk. Big gaps get canned foam and then tape for good measure. Canned foam seems like it's really sticky but there's always dusty spots or other things that create some short circuits for air leakage.
I second that, Peter!
Thanks for sharing this! I've been mulling how to deal with finishing the mostly-waterproofed-but-still-damp walls in the basement of my 100 yr old Cleveland home and this is the most promising solution I've seen thus far. It also looks ideal for solving both framing and insulation for the one remaining 19' exterior wall of my garage, which is brick + clay tile (the 1925 version of CMU in these parts).
For the garage wall, I'll probably get the 2" version and finish it with marine grade plywood so I can use the wall for storage. Question: should I fully air seal this wall, or leave some air gap at the bottom/top to be safe? The wall rarely gets wet (exterior brick protected by overhangs) and is east-facing with decent sunlight exposure, but the clay tiles do tend to channel and take on moisture. They've also been cemented and painted over on the inside, with probably already limits drying potential inward.
Thermal performance is not the priority as it's a semi-conditioned garage. There is a bonus room (my office) above, but the ceiling was vapor barrier'ed and insulated in a recent renovation. Recently when the temperature dipped into the teens, the garage stayed above 45F with its single steam radiator. Whatever improvement I get on top of that is icing on the cake - I'm mostly paranoid about messing up moisture management and damaging the masonry.
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