What Is A Floor Joist?

Stronger trees with good elasticity are ideal for floor joists, like the Ponderosa pine. Some popular choices include pine, fir, and spruce. These hardwoods, which you’ll notice are conifers, are great options and are easy to find.
A dead load is a permanent load. It comes from the structure and load of a building. But then live loads are temporary loads. They are applied over time, including traffic, furniture, and more. 

What Are Floor Joists?

Wood grade is important because lower grades indicate more defects, so it’s not structurally strong. So, the lower the number, the better the wood will be. With lumber graded wood, higher grades have fewer defects. Meanwhile, lumber with lower grades have a shorter life span. 
The floor joist plays a major role in residential construction. For a structural engineer, working with floor joists sizes is part of their job, yet a DIY enthusiast wouldn’t have a clue how to use them. When working with joists, there are many things to consider. You’ll need to know if you’re working with a bearing wall or foundation wall, as an example.
Different wood species have unique characteristics. Some are more flexible while others are stronger. Most of the time, slow growing trees, like the Douglas fir, are stronger. While fast-growing trees are soft wood.
If you choose 2x6s, you have to space them closer together, which would be less than 16 inches while you can space 2 x 12 24-inches apart. 

Types Of Floor Joists

Floor joist repairs should be handled by a professional. For simple repairs to floor joists, consider using a flitch plate. A flitch plate is a thin piece of steel or plywood that is bolted to a weak joist to offer support. However, another option is to use an identical board and secure it to the old one.
In residential floors, floor joist span will run the shorter width of a room. With ceilings that have rafters, they will run parallel to the rafters. 

Solid Lumber

Floor joists are designed to be load-bearing. They act as the support for upper levels, often transferring weight to vertical supports within a foundation. With upper levels, floor joists support the walls. 
Because of its price and a large array of options, solid lumber is the most popular type of floor joist. It’s easy to use, understand, and is the simplest type of floor joist. If you know anything about construction, then you can’t mess it up. 

I-Beams

The wood species used for floor joists include Douglas fir. Solid lumber is the cheapest type of floor joist if you use standard wood, rather than specialty wood. But in general, solid lumber is more fire-resistant and water-resistant than other options.
When it comes to the size of the boards, avoid using anything smaller than a 2 x 6. The largest you will use is a 2 x 12, but most common sizes will be 2 x 8 or 2 x 10. Though 2 x 6s are a common choice, they’re not your cheapest option.

Floor Trusses

Walls support the next floor. If a wall is placed parallel to the joists, it isn’t load-bearing. Only walls placed perpendicular to the floor joists can be load-bearing. For more info on load-bearing walls, check this article out. 
There are several factors affect floor joist spacing. The first thing is lumber grade, which can change the outcome by an inch or two. Board size also changes everything.

Load-Bearing Floor Joists

Using Grade-1 isn’t necessary as Grade-2 is flawless for most projects, including floor joist installation. You should avoid using Grade-3 or lower as it will risk the integrity of your foundation. 
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Supporting Structures

Supportive Framework

A floor joist is a horizontal beam, usually made of wood, that is used to support and enclose the flooring above a foundation. Floor joists transfer loads to the vertical beams of the house.

Load Capacity

On occasion, floor joists run perpendicular to rafters, when they typically run perpendicular. You should know that installing floor joists is not a DIY project for your home. And this applies to all DIYers. If you have problem with your floor joists, call a professional contractor. If you tamper with the joists in your home, you could be setting yourself up for major problems down the road. 

Floor Joists Building Codes

Because they are made with plywood, they can be cheaper than other options and can be stacked and glued to create a stronger board than what one single layer of plywood might be. This makes I-joists very strong. 
Shorter widths should be further apart. But this is an estimate depending on grade and selected integrity. The vertical boards and lengths of the horizontal boards are also important. 

Western red cedar, and Eastern white pine have low bending strength.

Repairing Floor Joists

Floor joist installation isn’t always necessary for a house because many floors are built directly onto a concrete slab. For homes built over basements or on wood foundations, floor joists are required for structural integrity. 
You can tell when you have a broken floor joist when you floor bounces or sags. You’ll also hear loud squeaking sounds.

Floor Joist Spacing

Joist spacing is the most important part of floor joist installation. If the joists are spaced too far from each other, they won’t work. On the other hand, if the floor joists are too close to each other, then it means you’ve spent too much money.
What you need to know is floor joists bear the weight of the entire home. While walls usually only bear part of the weight, with some not bearing any weight at all. Floor joists are important for this reason alone. 
Floor trusses are made with 2×4 wood planks on the top and bottom with a “web” of diagonal boards in the middle. The boards are secured with metal plates in the floor trusses. Because of their design, they use less wood than normal.
I-beams look like the letter I. The top and bottoms of the I are made with either solid wood or laminated veneer, but the center is made with plywood or OSB. They can span a longer distance than solid lumber.

• 2×6 – 12 inches
• 2×8 – 16 inches
• 2×10 – 24-inches

Wood joists should never be spaced more than 24-inches apart. So both 2x12s and 2x14s need to be spaced no further apart than 24-inches just like the 2x10s. 
Yes, termites eat floor joists. Termites eat wood, and this includes floor joists. You’ll know termites have attacked your floor joists when your floor structure begins to sag or your floorboards start rising. 

How To Choose The Best Boards For Floor Joists

Local building codes requires wood joists to support at least 10 pounds per square foot for a dead load and 30 pounds per square foot for a live load. Different wood, grades, span length, and so on affect the support per square foot. 
Unless you’re a structural engineer or professional contractor, it wouldn’t be a good idea for you engage in floor joist installation. You can paint your walls and install non load-bearing walls, but where structural integrity is concerned, floor joist installation is not a DIY project. 

Wood Type

Choosing boards for floor joists for an open web floor is can be difficult considering their importance. You need to know the differences between high bending strength and medium bending strength, for example. 

Wood Grade

A joist spans a ceiling and floor spaces in residential homes. Your floor at home has a load capacity and uses one of the many types of floor joists to transfer weight. Local building codes mandate that homes use floor joists. With floors or ceilings that have longer spans, heavier joists are required. 

Wood Size

The same goes for electricity and water. You wouldn’t put in your own septic. So keep a set list of things that you hire a contractor for. In the end, it will save you money, time, and a whole lot of restless nights. 
With floor joists, there isn’t much you need to know. However, it doesn’t hurt to be knowledgeable on the finer details of your home. You should be aware of the different materials that make up your floor system and how laminated veneer lumber and old growth trees are used. 

Floor Joist Conclusion

While the spacing codes have changed over the years, this is where we stand today. Here are the three most common spacings with floor joists and covers 90 percent of all types of spacings for floor joists. 
Most floor joists are single or double, and most often made with 2x6s or 2x8s. Though on occasion, they are made of 2x10s and tripled for additional support. But minimum floor joist sizes are never less than 2×6.
At this point, you’re probably wondering what the difference between a live load and a dead load. 
Floor trusses also have gaps that leave room to make wiring and plumbing much easier. However, crawlspaces are tricker with web floors because there isn’t enough room to crawl through like there would be with solid wood.