CRAWL SPACE FOUNDATION
According to data from the Survey of Construction, roughly 15% of new single-family homes have a crawl space foundation installed. The majority (54%) have a slab foundation, meaning that it is still the most popular choice. However, there are multiple reasons why architects and contractors may still suggest a crawl space foundation.
Crawl spaces are so named because they are spaces accessible only through crawling – with roughly 18 inches of clearance, they are not large enough to use as a livable space. They may, therefore, seem like a poor compromise between a full basement and a concrete slab foundation. However, they actually combine many of the benefits of both – as well as providing a solid, durable base to your home, they also provide for space to store plumbing systems and the electric panel.
If you want to learn about other kinds of foundation, visit our Types of Home Foundation page.
This guide will walk you through all of the different aspects of a crawl space foundation, from how it’s built, to costs, to the pros and cons.
CONSTRUCTION METHOD
Crawl space foundations are built by elevating the home off the floor by, on average, 18 inches. The foundation is built by using footing and block walls around the perimeter of the foundation to support the home. These footings are usually made with cinder, although many homeowners choose to layer the cinder blocks with bricks in order to give a more pleasant appearance.
The interior of a crawl space foundation may have supporting pillars throughout. You are left with a space between one and three feet high that extends the entire space of your home.
The flooring of the crawlspace is usually earth (i.e. it is not covered with anything), and the pillars are usually wooden. This gives a relatively spartan feel, although the crawl space is not intended to be a usable space.
Wiring and pipes usually run through the crawl space, but other than that, it remains empty unless you choose to add insulation (the advantages and disadvantages of doing so are discussed in the pros and cons section, below).
COSTS
For information on the costs of different types of foundations, see our guide Average Cost of Home Foundation, which will discuss all of the costs involved in more detail.
In general, however, the cost of a crawl space foundation is roughly $13 per square foot. For a standard-sized house, therefore, you can expect to pay between $10,300 and $19,400. This price includes materials and installation.
PROS OF
CRAWL SPACE FOUNDATION
Crawl space foundations have certain structural advantages over concrete slab foundations.
Although they are more difficult to install, they provide benefits in the long term that means they have the following advantages:
DURABLE
A major benefit of crawl space foundations is that they work in a wide variety of circumstances.
For example, in areas that are prone to earthquakes, a crawl space foundation is more likely to keep your house upright than a slab foundation (which is prone to cracking in response to the force of an earthquake).
UNEVEN GROUND
If you are building a home on a sloped piece of land, a crawl space foundation will allow you to create a level platform by varying the length of the piers in the base.
Since very few lots are perfectly level, this makes a crawl space foundation an attractive proposition.
FLEXIBILITY
In some soil types – such as those where soil contracts and expands – a crawl space foundation may be better suited than a concrete slab foundation. Crawl space foundations can often respond better to the hydrostatic pressure of some soil types than concrete slab foundations.
VENTILATION
Placing a crawl space under a home allows air to circulate underneath. In hot climates, this can help cool a home (although see below for the drawbacks of this).
ACCESSIBILITY
Perhaps the primary advantage of having a crawl space under your home is the ability to use the space to house your plumbing and electrical wiring. This not only keeps this out of the remainder of your house – thus freeing up space elsewhere – but also allows you (or a professional) access to your utilities if necessary.
STORAGE
Again, because of the space under your home, you are able to store items there that would otherwise be taking up space in your home.
Although crawl spaces are only 18 inches high on average, that still allows for smaller items to be placed there. In some respects, the crawl space is ideal for this – a basement may be usable space that you would rather fill with items that are not simply for storage; a crawl space isn’t space you would otherwise use.
FLOODING
A crawl space also serves to raise your home above ground level. If you have built a home on a flood plain, then that 18-inch rise could be the difference between a minor annoyance and a major disaster.
Although you will need to make sure your crawl space is free from moisture, having your home that little bit raised will give you peace of mind.
CONS OF
CRAWL SPACE FOUNDATION
Despite the advantages of a crawl space, there are also disadvantages.
It depends on your specific circumstances if any of the following limitations apply to you:
ENERGY EFFICIENCY
Although a crawl space can help keep your home cool in the summer, it can reduce energy efficiency in the winter. A large void of cool air immediately under your home is extremely inefficient in cold winters, and you’ll often spend money to heat the air in your crawl space.
You can fill a crawl space with insulation, although this removes some of the other benefits (such as storage).
PESTS
Because crawl spaces get heated by the house above, they can be attractive places for rodents and other pests. If rodents do make nests in your crawl space, it can be a while before you notice, and by then, they may have spread to other parts of your home.
A pest infestation will require a professional exterminator to remove it.
MOISTURE
Crawl spaces are prone to being damp. If they are damp for an extended period of time, they can damage the structure of the home. In many cases, the presence of moisture can also lead to mold infestations. If you do have mold in your crawl space, you’ll need to address it before it spreads to the rest of your home.
For more information on what causes water in a crawl space and how to fix it, see our guide on water in your crawl space.
WHEN A
CRAWL SPACE FOUNDATION IS THE BEST
OPTION
As suggested by the advantages above, there are specific circumstances in which an architect or a contractor may suggest a crawl space foundation as being best for your home. The default foundation is a slab foundation, so the reality of the situation is that, in most cases, a crawl space foundation works best in situations where a slab foundation is not best suited.
These scenarios include:
UNEVEN GROUND
When the grading of your land is not level, a crawl space will work better because of the ability to alter the height of the surrounding cinder blocks and internal piers to level off the home. This may lead to you having an uneven crawl space, but this in itself is not problematic.
FLOOD ZONES
Although crawl spaces can be problematic when it comes to allowing moisture to leave, they are certainly beneficial in areas prone to flooding. The fact that they are raised means that they give an additional 18 inches of clearance under which flood water can pass.
Once the waters have receded, however, you will need to work hard to ensure the water is fully removed from the crawl space or you will be affected by mold. However, this is preferable to having to replace furniture and other objects after your home has been flooded. Our page on who to call if you have water in your crawl space will help you with figuring out how to find the right people to fix the problem.
EARTHQUAKES
Crawl space foundations are far better than slab foundations when it comes to earthquakes. The lateral movements and general undulations of an earthquake mean that it will crack a slab foundation relatively easily.
By contrast, a crawl space foundation is much more flexible.
Ultimately, if you are one of the 15% of homeowners with a new crawl space foundation then you are already aware of the potential benefits a crawl space brings to your home. In times of flooding, you can rest a little easier knowing your home is raised; you also have a great place to store unsightly pipes and electrical wiring.
Although a crawl space does require more maintenance than a simple slab foundation, it is easier to manage than a basement. Indeed, overall, it combines many of the benefits of the two, without having many of the weaknesses of either.
If you live in an area prone to flooding or earthquakes, or are building on uneven land, or have soil unsuited to a concrete slab foundation, then a crawl space could be the best option for you.