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How to convert a crawl space into a basement

If you have a crawl space under your house, it’s possible to convert it into additional square footage for you to live in. Sound complicated? It doesn’t need to be with a detailed design plan and the right team at your side. But the question remains: How do you convert a crawl space into a basement you can use? The answer: Very carefully.

As a contractor specializing in custom remodel solutions, Lamont Bros. has worked with several Portland-area homeowners who needed to increase their square footage. Although converting a crawl space into a basement isn’t a simple process, it can dramatically increase the amount of living space in your home.

In this article, you can learn more about converting crawl space into finished space. We’ll help you learn about what this type of remodel entails so you can decide if it’s right for your home. Specifically, we’ll discuss:

Why should I convert my crawl space into a basement?

Most of the time, a crawl space conversion is considered a “last resort” type of project due to the high cost. However, converting a crawl space is a decision that makes the most sense under these specific circumstances:

There is nowhere to go but down

Love your home, but need more space? If you can’t add to the side of your home with a traditional addition or the top of your home with a second-story addition, a crawl-space conversion may be for you. 

There are a handful of reasons why expanding downward could be the only option for an addition. The property lines may prevent you from expanding outward. Perhaps a tree stands in your way, which can be expensive to work around. If your home already has a second story, it can be difficult to add a third. Other times, a single-level home’s structure simply can’t handle the added load of another level.

When you’re unable to expand your home in the more traditional ways, converting your crawl space can save the day. However, that’s only if your heart is set on staying in the home you’re in. Moving to a larger home is often less expensive than a crawl space conversion.

Converting crawl space to a basement is a great way to increase living space in your home.

You currently have a partial basement foundation

Some homes have a split foundation — one part is a standard-height basement, while the other part is a shorter crawl space. Partial basement foundations are most common in homes built on a slope. The basement portion is usually a daylight basement with an external door and windows.

In the case of a partial basement, it often makes sense to convert the remaining crawl space into finished basement space, as well. Because there is usually already an access door and room to work, the project cost tends to be lower than a full crawl space conversion, as well. 

A basement makes the most sense for the space’s purpose

Perhaps you have a specific, non-traditional use in mind for the space you’re adding to your home. Depending on the purpose of the space, adding it to a lower level might make the most sense.

For example, consider an indoor swimming pool room. That would be incredibly difficult to add to a second story. In most cases, an addition to the side of your home would make the most sense, but if you can’t build outward, you could put a pool into the basement, instead. 

The same goes for any type of room that requires silence, isolation, or darkness. That’s why a crawl space conversion makes a lot of sense for home movie theaters or recording studios. Below-ground living space is naturally sound absorbent and lets in less daylight. Home gyms and activity rooms are also strong candidates for crawl-space conversions. 

What is the process to convert a crawl space into a basement?

Once you decide if a crawl space conversion is right for you, it’s time to get to work. There are several features that a basement must have to be considered a “living space.” Below are the goals that a good crawl space conversion will achieve.

Standard ceiling head height

The head height of a basement is the vertical distance from the floor to the ceiling. According to Portland building code, the ceiling must be at least 6 feet 8 inches to be legally designated “living space.” This number is the bare minimum required by law; at Lamont Bros, we typically recommend at least 7 feet, six inches if possible.  

The head height is usually the first step in changing a crawl space to a basement because it’s the one that requires the most work. Most crawl spaces are usually about 4 feet tall, so you’ll have to come up with at least 3 more feet of additional head space. There are two options to achieve this goal.

Floor dig-down

The first option is to dig your crawlspace floor down until you have enough headroom. This process often involves heavy digging machinery and hundreds of labor hours spent digging the crawl space and transporting the dirt out.

Once that’s done, a professional concrete contractor must extend the foundation down to the new level and ensure that it will support the weight of the home above. Dig downs are most common among partial basements and crawl spaces with dirt floors.

House lift

Option number two is to perform a house lift. This type of project raises your basement head height by lifting the home rather than lowering the floor. It involves hours of project planning and the help of specialty house-lifting contractors. Once raised to the appropriate level, the foundation must then be extended up to meet the home.

A house lift is usually the most appropriate way of raising a basement’s head height under specific conditions. The most common reason you’ll see a house lift project is because the foundation is already compromised and needs to be replaced. It may also make sense to do a house lift if your crawl space has a concrete floor, which is rare. In this case, it would take a long time and a lot of work to tear up the slab, so building upwards may make more sense.

To learn more about raising the head height of a basement, check out this article

Proper waterproofing measures

After establishing an acceptable head height, the next step in converting a crawl space is to address any waterproofing issues. Water can damage finish materials like wood framing, drywall, and flooring, so it’s important to solve any water intrusion issues before finishing the space. 

Unfortunately, it’s not uncommon for groundwater to seep through crawlspace walls that haven’t been properly waterproofed. This is an especially common problem in older homes.

The issue with addressing waterproofing issues is that it’s often hit or miss. For some homes, the land was properly surveyed before construction and the crawl space was waterproofed when it was built. For other homes, water seepage may require several steps to be taken to solve the issue. 

Often, waterproofing begins by addressing the downspouts from the roof. Some improperly placed water drainage systems can channel water towards the basement instead of away. Other times, a home requires re-sealing the foundation walls to keep out any more moisture. 

In some rare cases, a house may have been built directly over a natural spring. As a result, there’s a literal creek running through the foundation. This happens in geographically hilly regions that receive a lot of rainfall. West Linn, Oregon City, and Portland’s West Hills frequently experience seasonal creeks through private properties. If a creek like this develops directly under your home, you’d have to hire a geotechnical engineer to design a method for diverting the water before moving the project forward.

Installing basement access & egress windows

After waterproofing, now it’s time to find a way for you to access your new basement space. There are two primary approaches to basement access: interior and exterior.

With exterior access, you enter the basement through a door to the outside. Usually, this includes exterior steps leading down to the door rather than interior steps leading up. You’ll find exterior basement access doors in most basement ADUs to give tenants their own door to the space. 

If you plan to incorporate your new basement as part of the existing single-family home, then an interior staircase might be the better option. The challenge with an interior staircase is that it takes up space not only in the basement but also from the floor above. If you already have a staircase in your home, it’s best to build the stairs underneath the existing staircase. This promotes design functionality by keeping all the stairs in the home together. It also saves on space since that area on the upper floor is already occupied by a stairwell. 

Then, there’s the issue of egress windows. By law, every bedroom in a home must have a window or exterior door large enough to escape through. Even if none of the rooms in your basement are intended as bedrooms, it’s still a good idea to provide an egress window for safety reasons. They also let in natural light, which can add to the comfort of the space. You’ll want to consider how many egress windows you want in your basement and where they should go.

Egress windows are an important feature that ensures your basement meets building codes.

Space design and use

Once you’ve worked out the bare necessities, it’s time to start designing the space to fit your taste. The general use of your new basement will affect how you incorporate the above factors into the design. However, once you’ve worked out the major details required for safety and legal purposes, the basement’s your oyster.

Now begins the fun part – you’ll get to choose design features, fill in the big picture with little details, and make the space your own. Start with the general layout of the space — what do you want where? Will there be bedrooms or bathrooms? If so, how big, and where will they go? You’ll also need to select finishes, including any cabinets, paint colors, light fixtures, flooring material, and door styles. 

Want a designer’s help converting your crawl space?

Now that you have a firm understanding of how to convert a crawl space into a basement, take the next step. Check out our basement remodeling portfolio, where you can see examples of our previous basement remodels and begin to gather inspiration for your own. 

When you’re ready to convert your crawl space into a basement, don’t do it alone! The process requires careful planning, expert builders, and hundreds of labor hours. Click the button below to schedule a free consultation with a member of our design team. We’ll help you plan your crawl space conversion, design a custom new basement, and even build it with the help of our in-house design-build team.