Continuous Masonry Foundation Vs Crawl Space

Choosing between slab vs. crawl space foundations deserves a little extra research consideration. When built correctly and when suited to the land your house is on, a foundation can last forever. Both slab foundations and crawl spaces have the potential to be that forever foundation, but the two designs aren't interchangeable.

If you use a slab foundation where a crawl space should have been, you'll end up with a cracked slab and a massive bill. If you put a crawl space where a slab should have been, you could end up with chronic pest problems as well as higher utility bills. Keep reading to learn more about what each foundation does and when it makes sense to use each one.

Contents [ show ]

• What Is a Slab Foundation?
  • When to Choose a Slab Foundation
• What Is a Crawl Space?
  • When to Choose a Crawl Space
• Final Thoughts

What Is a Slab Foundation?

A slab foundation is a solid piece of concrete that sits underneath your house. It's typically four to six inches thick and sits on top of a layer of sand. The sand provides drainage and creates a cushion to absorb shock from any movement in the earth around your home. The slab itself is usually reinforced with rebar or tension cables so that it can bear the weight of the house.

Typically, a slab foundation costs less and is easier to install than a crawl space. It's also less prone to pests since it doesn't create open space where termites or other critters can get in and start eating away at the wood.

Finally, slab foundations are ideal when you don't want stairs in your home. Crawl spaces usually end up lifting the house a little above ground level, which makes steps or a ramp necessary to lead to the entrance. Slab foundations are level with the ground so you can avoid steps or ramps. This makes it a great choice for anyone who might have difficulty with stairs or for families with young children.

While they're pest-resistant and cost-efficient, slab foundations are more vulnerable to cracks. Earthquakes, shifting soil, floods, and other issues can cause cracks that will need urgent (and costly) repairs. This vulnerability makes them less suited to climates where you're more likely to experience the things that can hurt a foundation.

When to Choose a Slab Foundation

Despite its vulnerability to cracking, slab foundations are still a great pick for lots of different scenarios. Here are some of the cases where a slab foundation might make the most sense:

• Your house is in a warm climate where flooding and earthquakes aren't likely.
• Your house is being built on relatively flat land (not on the side of a slope).
• You need to build a house with no stairs.
• You live in a humid climate where pests or mold are a bigger problem.
• You are under significant budget or time constraints to get this construction project done.
• You don't expect to make significant remodeling decisions later. The wiring and plumbing of your home will be embedded into the concrete slab so if you want to reconfigure the layout, it'll be tough to redirect plumbing or wiring to do so. Plans for expansions and add-ons will be fine but if you expect to, say, swap the kitchen and the dining room, you'd need to dig up your concrete foundation to do it, which will weaken the structural integrity.

Depending on which of the above sounds most like your scenario, you might have some additional considerations:

When Flooding Is a Problem

The main risk with flooding is that the force of the water will create or worsen cracks in your slab. This means flooding that results from hurricanes or other aggressive weather patterns is the biggest problem. The impact of sudden flooding could cause serious damage. Crawl spaces are better equipped to resist damage from the force of impact.

If the flooding you're more at risk for is not as forceful because it's, say, overflow from the river and you live in a river basin or excess rainwater paired with poor drainage because you live somewhere that doesn't get predictable rain, the slab will probably tolerate it alright.

With that said, if you live somewhere that experiences freezing temperatures at any point, any kind of flooding will be a problem. Leftover moisture inside the concrete that freezes into ice and then melts away with the thaw will weaken the structural integrity of your concrete.

For any type of flooding, you want to make sure the soil around your home drains well. The longer water pools around slab foundations, the weaker the concrete gets. So have the area inspected for drainage problems and make sure you fix those before or during the foundation installation.

When Pests and Mold Are a Problem

While slabs are generally recommended for humid climates where mold or pest infestations are a top concern, they aren't a solution all on their own. If you're choosing slab for this reason, make sure you're also choosing mold-resistant and pest-resistant materials in other parts of your home as well.

For example, pests that can't get in from underneath can still chew their way through walls or get in through poorly insulated door and window frames. During construction, keep an eye out for these common oversights in foundation construction as well:

• Use sharp gravel instead of sand under your slab to discourage burrowing creatures from weakening the integrity of the cushioning layer under your foundation. Also, make this gravel layer at least 18 inches.
  Make sure the slab has at least 6-inch clearance above ground so that the exterior siding of your home won't touch soil. Direct contact between wood and soil increases the risk of infestations.
• Apply a nontoxic pretreatment to the gravel layer and the frame of your house. This is an insecticide that will deter pests for 3-5 years. You'll then need to start doing periodic treatments around the perimeter of your house after that.
• When framing the walls, gaps between the frame and the concrete should be no more than 0.4 inches wide. This is just under a ½-inch (the smallest opening a rodent can get through) but still wide enough to allow some flexibility as the house settles. If it's more than 0.4 inches, use concrete caulk to seal it.
  Inspect and seal cracks in foundation, even tiny ones, every year.

What Is a Crawl Space?

A crawl space is an open area underneath your open, bounded by thick walls. It usually features load-bearing beams or additional support walls throughout the area but is otherwise open. These masonry walls are a little more flexible so that when soil erodes in a flood or an earthquake shakes the foundation, the foundation can move with it instead of cracking like a slab might.

With a crawl space, your home will usually be raised about 18 inches or so above ground level. This creates just enough space for you to access plumbing or wiring if you need to make any repairs. It can also be built high enough to keep your house above base flood elevation.

The raised design of a crawl space also makes them more adaptable to uneven ground. If you're building on the side of a slope, you can use a crawl space foundation to create a flat surface to build on.

While they are easier to repair and make for easier repairs of plumbing and wiring, the open design also makes them less durable, less energy efficient, and more vulnerable to pests. Those with mobility issues will also need to rely on ramps to access the home because crawl spaces elevate homes above ground level.

When to Choose a Crawl Space

Crawl spaces are more expensive than slab foundations and require more ongoing maintenance but they're still a more versatile and adaptable option, especially in the following situations:

• You live in a cold climate where freezing temperatures happen every year.
• You're building on an uneven ground, such as the side of a slope.
• You live in a dry climate where mold and pests aren't as much of an issue.
• You live in a disaster-prone area where a slab foundation would be too at-risk of breaking.
• You want the option to make significant remodeling decisions later on. This might be the case if, say, you're building a multifamily property now but want the option to convert it into a single-family home later.
• A crawl space will make it easier to reconfigure the layout.

Even though a crawl space is a lot more versatile, it's still vulnerable to damage. Save yourself a lot of stress later by taking some extra steps to customize your crawl space to your climate and threats you're prone to:

When You Live in Earthquake Country

Crawl spaces may be a better choice than slab in earthquake prone areas, but they aren't invulnerable to damage. If you live somewhere with frequent earthquakes, you should take these extra steps to earthquake-proof your crawl space:

• Install anchor bolts every four to 6 feet to secure the walls to their foundation slabs.
• Surround the crawl space walls with cripple walls. These are basically shock absorbers for your foundation.
• Inspect the mortar between the masonry annually. Crumbling mortar isn't actually holding the blocks together which means the next earthquake could knock over your foundation as easily as a kid knocks over a block tower.

When Pests Are a Problem

If you need a crawl space for one reason or another but you're also building in a region where pests will be a threat, your crawl space will make your home extra vulnerable. Here's how you can keep those threats to a minimum:

• Install curtain walls or steel wire mesh around your foundation walls that extend 36 inches below ground. This will prevent pests from burrowing into your crawl space.
• Inspect and repair mortar annually. Pests, like rats, can squeeze through gaps between masonry with ease if the mortar is weak.
• Place a layer of sheet metal or other pest-proof material under your floor and around the outside of the frame (i.e.- underneath where your exterior siding will go). This will prevent pests from chewing or burrowing their way inside your house and walls.
• Seal cracks and gaps with caulk. Check for these annually.
• Use encapsulation and vapor barriers to prevent moisture from causing long term damage to your capsulate. A stronger crawl space is less vulnerable to pest infestation.

When Flooding Is a Problem

If you live in a flood-prone area, especially if you're worried about flash flooding, make sure you modify your crawl space a bit to manage the damage caused by flood water. Here are a couple tips:

• Install flood vents. These are small holes placed throughout the base of the walls to allow water to flow through one side and out there instead of just slamming up against the wall. They also encourage faster drainage and can help prevent damage from the high winds of hurricanes and related disasters.
• Fix drainage problems. Just as with slab foundations, crawl spaces will do better if the soil around them has proper drainage. Crawl spaces are already more mold-prone and the longer water pools around them, the more those mold spores have a chance to build a thriving community under your house.
• Install HVAC systems, ductwork, and other equipment above the flood line. Keep damage to a minimum by making sure your wiring, plumbing, ducts, and other features of your home are built close to the floor and that the crawl space is tall enough to keep those above the base flood elevation of your area.

Final Thoughts

Choosing the foundation for your home is no easy task. It's a decision that will remain with you for decades, or in some cases, forever. For this reason, it's important to weigh your options and choose carefully. This guide has given you everything you need to know, so you can feel comfortable choosing between slab and crawl space foundations.

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Source: https://tooldigest.com/slab-vs-crawl-space/

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