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What Is a Floor Joist?: The Structure of Your Crawl Space

floor joists

Floor joist systems are pretty common in homes with basements and crawl spaces all over the Midwest, especially in Michigan. This system is what provides support for almost everything in your home. As such, it’s key to maintain them in the best possible condition.

Here’s what you need to know.

What Are Floor Joists?

Floor joists are structural members that, alongside floor framing, stiffen the subfloor shearing. Construction crews install them after they finish working on the basement or crawl space, depending on the type of lower-grade structure a home has.

When properly installed, floor joists will support the flooring above them. To do so, they need to be parallel and perfectly equidistant. Therefore, constructing them is not a DIY project an ordinary homeowner can do. They require skilled professionals since the structural integrity of the whole building will rely on choosing the correct type of joists.

Floor Joist Types

Floor joists come in several types. Each one of them has its pros and cons. Here are three of the most common ones.

1. I-Joists

First, we’ll start with an eco-friendly type. I-joists aren’t made entirely from solid wood. Their ends are wooden, and the middle is made of OSB or plywood. They look like the letter “I”, hence their name. These floor joists can extend more than 20 feet and have a higher weight load capacity. This makes them perfect for tile floorings. It’s also worthy to mention that some types of I-joists come with predrilled holes, making them ideal for utility lines.

2. Solid Lumber

The second type of floor joists is made of solid lumber. Years ago, they were the most common joist types that homeowners would use. Their biggest pro is their price. Solid lumber joists are pretty affordable, and their cost will depend on their size, wood grade, and wood type. Another pro is how good they deal with potential fires. If you’re looking to use them, it’s key to follow local construction codes and also keep utility holes in mind.

3. Open-Web Floor Trusses

The last type we’re going to mention is open-web floor trusses. They are made of two-by-four-inch boards that look like a web of diagonals. Open-web floor trusses connect with plates that help keep them in place. What makes them perfect for running utility lines through is the space between the diagonal boards. Another pro of this floor joist type is that they’re much easier to construct than their previous two counterparts. Essentially, they’re a great budget choice.

What Causes Floor Joists to Fail?

  • Poor support design: Without a proper design or over-spanning, floor joists will fail sooner or later. The design dictates their ability to support the load above. If there’s extra weight, they will eventually weaken and sag as a result of too few joists being used.
  • The weight of the home: Adding a floor to your home might cause the floor joists to fail. This is because the original engineering calculations didn’t include the extra weight that you’re looking to add. It’s key to keep this in mind if you’re looking to renovate your home and increase your living space.
  • Moisture and humidity: Waterproofing your home is essential, no matter where you live. If you allow excess water into your lower-grade level, it will cause serious structural damage which will, in turn, put you in harm’s way.
water in crawl space

How to Spot Failing Floor Joists

failing floor joist

The main disadvantage of floor joists is that they are made of wood. And as such, they’re prone to problems like rot and decay. Hence, if you notice uneven floors, or skewed windows and doors, it’s best to contact professional help. On the other hand, it’s key to pay attention to sinking crawl space supports, rotting and moist wood, drywall cracks, and creaking floors.

We should point out that it’s not the best idea to try and fix a failing floor joist by yourself. These problems require experienced contractors or carpenters. So, if you notice any problems, be sure to contact a structural engineer to first assess the state of your joists and recommend further repairs. The more you wait, the more time you’ll allow for the problem to grow.

Fixing Failing Floor Joists

The first and most important thing you can do is prevent moisture in your home. Since floor joists come from wood, they’re prone to rot in wet conditions. To deal with this issue, it’s best to waterproof your basement or crawl space. On the other hand, if the damage is already present, you might need to replace them entirely. Again, you can’t do this on your own. This is much more complex than dealing with small-time repairs.

If you live in the Detroit area, Grand Rapids, or Traverse City in Michigan, you can contact FSM. Our experienced team can visit your home and carry out a free, no-obligation inspection. After providing you with a free estimate, we’ll be able to offer you numerous waterproofing solutions for your lower-grade area. It’s better to invest in your floor joists and be carefree for years to come than risk your family’s comfort and safety due to high moisture and rot.

Floor Joist FAQs

The timeframe for repairing over spanned floor joists depends on the severity of the damage, the size of the affected area, and the selected repair method. Foundation Systems of Michigan’s experienced crews aim to minimize inconvenience and complete repairs promptly. A detailed timeline will be provided during your free inspection visit. 

Floors may sag or become unlevel due to overly stretched joists, insufficient support structures, moisture-damaged joists, and high humidity levels. These factors can cause noisy floors, a cluttered look, and potential tripping hazards. Foundation Systems of Michigan’s specialists will pinpoint the precise reasons for floor issues during a complimentary inspection and suggest custom repair strategies, including the IntelliJack™ Crawl Space Jacks. 

Costs can fluctuate depending on the damage extent, repair area size, and selected solutions. Our professionals at Foundation Systems of Michigan will provide a precise estimate after a no-obligation inspection, including information on payment plans and financing options.

Leah Leitow

Leah Leitow

Content Writer

Leah is a Content Writer for Groundworks with nearly ten years of experience working in the foundation repair industry. Her experience ranges from working with homeowners to find the right solution to training inspectors and staff. In her background as a Michigan journalist, she gained invaluable insight into people's lives throughout our state. Leah lives in metro Detroit with her husband and two sons.

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