Is a crawlspace foundation a good choice for your next build?
Foreword by Ian Thompson, Editor
Why don’t we build more with suspended ground floors and crawl spaces underneath our houses and buildings? This question is particularly pertinent in Australasia, where slab-on-grade foundations are prevalent. It’s a conundrum that we will address in this video, along with why they are used and why they are effective.
Slab-on-grade foundations, while relatively easy to construct, can consume a lot of concrete, which implies a significant environmental impact and high costs. Additionally, and importantly we often overlook the fact that they are not ideal for services maintenance and replacement, particularly when something goes wrong. If you have to repair a drainage line then you have to rip the whole slab open which is not only expensive but very disruptive to the home owner.
So, why aren’t we employing more pad, ring, raft, or pier and beam foundations? Each of these foundation types has its own set of advantages and disadvantages, and their suitability depends largely on the specific climate and site conditions.
Pad foundations, for instance, are best suited for lighter structures and are relatively inexpensive to construct. However, they are not ideal for areas with expansive or soft soils, but it doesn’t mean that we can’t use them, it just means we have to be a bit smarter in our substructure design.
Ring foundations, on the other hand, are often used in cyclone-prone areas because they provide excellent wind resistance. However, they can be more expensive to construct due to the need for extra reinforced concrete and steel.
Raft foundations distribute the load of the building evenly across the ground, making them suitable for soils with low bearing capacity. However, they can also be expensive and time-consuming to construct, and they may not be feasible in areas with a high water table, and as mentioned earlier they are the worst type of foundation for maintenance.
Lastly, pier and beam foundations are good for homes in flood-prone areas, allowing for easy access to utilities and providing a buffer against ground moisture. However, they can be susceptible to damage from pests and rot if not properly maintained.
Regardless of the type of foundation used, the primary consideration should always be the suitability of the foundation to the climate, soil conditions and maintenance. For me a conditioned or non-conditioned crawlspace is something that I would like to consider more, particularly for ease of futureproofing my services and easy maintenance.
Conditioned crawl spaces, as Matt discusses in this American specific video, offer a viable alternative to traditional basements in areas with a high water table. These spaces can house essential utilities and can be sealed to ensure airtightness, and pest prevention, providing an effective solution to the challenges posed by traditional slab-on-grade foundations.
Welcome back to another exciting episode of the Build Show with Matt Reisinger and Wade Baquin. Today, we’re delving into the world of conditioned crawl spaces, and trust us, it’s going to blow your mind. But before we get into all the nitty-gritty details, let’s address a burning question—why did they opt for a crawl space instead of a full basement for this stunning waterfront house? Well, it turns out the water table in this area is remarkably high due to the abundance of ledge. To combat this, they’ve implemented clever strategies like a curtain drain to manage the water table. However, the conditions still called for a crawl space, offering a perfect spot for essential utilities like ductwork and MEPs. Wade’s expertise in creating an optimal crawl space shines through, and Matt is thoroughly impressed with the meticulous craftsmanship. From the innovative concrete slab to the sealing techniques that ensure airtightness, this episode is packed with valuable insights. So grab your hard hat and join us on this enlightening journey into the world of conditioned crawl spaces. Stay tuned for more incredible content from Wade and the team over at buildshownetwork.com. And don’t forget to follow us on TikTok and Instagram for some behind-the-scenes fun. Until next time, happy building!
“What’s up guys? I’m Matt Reisinger, and I’m Wade Baquin. And on the Build Show today, conditioned crawl space. Let’s get going.”
“Alright, Wade, we’re visiting one of your jobs right here on an incredible lot right in the water. We’re talking about conditioned crawl spaces. But first off, before we get into the details on this conditioned crawl space, why not a full basement for this house?”
“It’s a great question, Matt. Um, so we are in an area that has a very high water table, and that is mostly driven by the fact that there’s a lot of ledge here. And we know water likes to follow ledge. So there are a couple of things already going on here on the site that help mitigate that. Outside of the perimeter here of the foundation, we’ve got what’s called a curtain drain. So on three sides of the property, right where it slopes down to the water, the sides and the back have a curtain drain to pick up the water table and help get that out. But it’s still really bad. Yeah, and so we couldn’t get a full-depth basement in here. We wanted a crawl space so we could get some of our ductwork and some of the MEPS, if you will, down here and not have like a slab on grade. I love a good crawl space, and this is textbook, Wade.”
“This beam right here will have joists sitting up on top of it, that I’m assuming. And then on top of the mud seal is going to be the top of plywood, is that right?”
“Yeah, so we’ll have some engineered joists going in this direction here that will sit flush with that PT. Okay, and the plywood’s going to come over the top of that. Got it. So, in other words, you’ve got a solid three or four feet. Walk me through this concrete slab and how and when you put the slab in.”
“Sure. So, you know, this is one of our trademark details. I credit you with pioneering this approach. Thank you. I don’t know if someone else has done it before me, but it’s something we like to use often because it works. So we’ve got our foundation in, we’ve got that backfilled, we’ve set our subgrade here within the foundation, compact gravel, so anything virgin would have stayed where we’re backfilling in around the perimeter. The overdig of the foundation is going to get the gravel compacted, and then below the slab, six inches of three-quarter-inch, what we call around here, crushed stone. Some people call that gravel or wash gravel. Basically, you know, three-inch size, kind of jagged stone. Yeah, that’s compacted. And then we come in and we apply that closed-cell spray foam. So we’ve got about, on average, two and a half inches, gotcha, underneath where we’re standing on the slab. It’s all monolithic. It comes up the sidewalls here in the foundation, 12 to 18 inches. We feather that out back to about, you know, half inch, inch. When we’re weathertight, we can continue the foam where we left off, overlapping that, continuing it to be monolithic and carry that up to the underside of our subfloor. That’s beautiful.”
“So now this slab that we’re standing on is floating on top of that closed-cell, but it’s really, I mean, that closed-cell is incredible, very high, 25 psi, I believe.”
“It’s very high. Way, you’re not going to move or squish or anything on this slab.”
“Absolutely not. The other beauty of this slab is that you can clean this up for your clients and make this really nice down here. And what I’ve done in the past is I’ve put a mechanics creeper down in the basement. So if I need to service anything, yeah, I can roll around with the flashlight and get into every corner and see exactly what it’s looking like.”
“Yeah, absolutely. The other thing I’m noticing, which is correct, no venting. You know, most crawl spaces are pretty gross. There are rats and raccoons and spiders and all kinds of stuff. There are no vents to the outside. So this is, in effect, a short basement, just like you build a basement, just with not much head height.”
“It is, yeah. And because of this application, it will stay dry, which means we’ll have good air, which means it won’t be your typical musty, smelly basement. Yep. You know, and worst case scenario, if you have to throw a dehumidifier down here, yeah. So yeah, you could just do a 300 plug-in one that you get at the hardware store or even like a Santa Fe if you want to do something on the, you know, higher, nicer end. Sure, but most likely not needed. Yeah, I really like this, Wade. This is textbook.”
“Okay, before we leave, I want to show you guys one other detail that Wade does on all his projects that I really like. Wade, walk me through your mud sill and how you’re using this standard sill sealer but taking it to the next level.”
“Sure. So, you know, we use this a lot on most construction sites. It’s your capillary break, right? But this connection, right wood to concrete, as you know, is one of the most important connections on the home. For sure. It’s an area that’s prone to leaks, for bugs and the bug path. Sure, big time. So what we do is before anything goes down on top of the concrete, we’ll run a bead of… You can use different types of sealants here. We’re using Big Stretch in the gray color.”
“And you’re noticing where you guys did it down here, they overdid it, so you can kind of see what they did. But they’re putting a bead or two on the concrete first. And then talk to me about this bead here that’s kind of sticking out.”
“Yep. So that first bead goes on about, you know, a half inch to an inch in from the face of the concrete, the foundation face. And then what the guys are doing is they’re putting a bead on the underside of this PT. Then they’re stapling the sill sealer onto it. So now you have this as one piece that they can control and put this down, so it’s nice and neat. So now you have a bead of sealant, capillary break, bead of sealant, wood, and then we crank that down with the anchor bolts. It makes a nice little sealant sandwich, and we’re nice and airtight. And you’ve got a little bit of squeeze-out right here that Ivan and the crew did. They did a really nice job, guys.”
“Yeah, you know, it’s nice and compressed down in there, and you have a nice tight seal. And no matter whether you’re doing a crawl space, conditioned crawl space, or a basement, that’s a great detail, Wade.”
“And see what it all has happened, and it’s not expensive. You know, a case or so of this for a foundation this size, it’s peanuts in the overall budget for the project. And what you get out of it is obviously atremendous amount of value. Last detail I want to point out too, Ivan the framer, where his PT seal is coming up against this wall here, he also put it on the end of the board where it’s coming into the foundation. So he’s thinking about those details. You’ve obviously taught them the reason behind it, not just saying, “Hey, do this detail right.” You’ve got a smart framer who knows what he’s doing. We went over those details, and I certainly did remind him where we have some of those vertical connections that we want to make sure we’re getting sealant there as well. Yeah, good work, dude. Love it.