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Floor Joist

Floor joists support the floor and tie the walls together, keeping your home in place. Here is how to keep these joists in the best possible shape.

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Floor joists are used to support floors that span over open areas, such as a basement or a crawl space. Their main purpose is to support the floor, but they are also used to tie the walls together, making the home much more stable. Since they have such an important role, they need to be built properly and regularly maintained. Read on to learn more about floor joists, the types that exist, and their most common problems. 

floor joist

What Is a Floor Joist? 

If you built a house on an empty lot or you passed by a construction site at some point, you have surely seen wooden frames placed above the foundation. Floor joists are those parallel, flat structures that are connected to the floor framing and together stiffen the subfloor shearing. These joists look like mini bridges that are only connected at the end to the frame. The floor joist system is put in place after the foundation has been constructed. When the joists are installed, they provide support to the floor above. To properly support the floor, beams need to be equidistant. Since there are so many things that need to be taken into consideration, installing floor joists should never be a DIY project. Only experienced and skilled contractors can pick the right type of joists for the structure and install them correctly. 

Types of Floor Joists 

Usually, contractors choose from the three types of joists based on their needs. Each of these types has its flaws and upsides, so it is important to assess the situation and see which floor joist will provide the best support. 


When it comes to the I-joists, only their ends are made of solid wood. Since they are mostly made of OSB or plywood, this is the most eco-friendly type of joist. They look like the letter “I”, which is how they got their name. Since they can span over an area that is more than 20 feet long and have a high weight load capacity, they are mostly used for tile flooring. Some I-joists come with predrilled holes, so the contractors can put utility lines through them. 

Solid Lumber 

Floor joists made from solid lumber are the oldest kind. Before the construction materials became as advanced as they are today, homeowners had no other choice but to use these joists. They are cheaper than other joists, and their price depends on their size, wood grade, and wood type. The best thing about solid lumber joists is that they hold up well against fires. During the installation, it is important to make sure that everything is up to code and not to forget holes for utility lines. 

Open-Web Floor Trusses 

These joists have so many upsides and are very popular with contractors. Open-web floor trusses are made from 2 x 4 boards and look like a web of diagonal boards connected with plates. The space between the diagonal boards makes the installation of the utility lines so much easier. Open web floor trusses can span over much larger areas due to their unique design. On top of that, these joists are also much easier and quicker to install, so they are often the economical choice. 

Signs of Failing Floor Joists 

Since each type of floor joist contains some amount of wood, they are prone to rotting and decay. If you are wondering how your floor joists are holding up, there are several signs you should keep your eyes open for. Uneven floors, skewed window or door frames, or sinking crawl space supports are all red flags that are alerting you that something is wrong with the joists. In addition, problems such as rotting and moist wood, cracks in your drywall, and creaking floors are also signs that your floor joists are failing. If you notice any of these signs, do not try to repair the damage by yourself. Instead, contact professional contractors in your area who will thoroughly inspect the joist system, detect any problems and recommend suitable repair solutions. 

Causes of Problems with Floor Joists 

Several factors can impact your floor joists and cause them to malfunction

Poor support design: It is extremely important that the spacing is calculated correctly and that enough joists are used to support the load above. If the joists are not designed or installed properly, they won’t be able to carry the load and, in time, they will begin to sag

The weight of your home: Building another story or expanding your home in some other way can add extra weight to the structure. Since the floor joists were designed and installed with original plans in mind, they won’t be able to carry the extra load and will begin to crack. 

Moisture and humidity: Moisture leads to rot and since all floor joists are at least partially made of wood, this can be a serious problem. This is why it is important to waterproof your basement or your crawl space and avoid such issues. 

How to Fix These Problems 

To keep your floor joists in the best possible shape, you need to keep the humidity levels in your home under control. Otherwise, the joists will begin to rot. Waterproofing your foundation is necessary if you want to avoid these problems. To avoid replacing entire joists, fix broken ones as soon as possible. If your floor joists are no longer able to bear the load on their own, SettleStop Floor Supports can provide the reinforcement they need and prevent sagging floors. 

Damaged floor joists should be repaired as quickly as possible. If you have noticed the common signs of floor joist failure, call the experts at AFS. We proudly serve areas of Tennessee, Mississippi, Alabama, and Georgia, so contact us today and schedule a free inspection and repair quote

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