Skip to Main Content

Over Spanned Floor Joists

If your home has a crawl space, the floors inside are being supported by floor joists. Anything that damages these integral structures is also going to damage your floors.

Schedule Free Inspection

Floor joists are a type of support beam found in crawl spaces. Their main function is to prevent the main floor of your home from collapsing. For that reason, damage to floor joists will lead to damage to your floors, and eventually the structural integrity of your home. What causes over spanned floor joists in the first place? 

What Causes Over Spanned Floor Joists? 

Over spanned floor joists are usually the result of moisture problems or construction errors. Generally, moisture problems arise because crawl spaces are not built with moisture protection in mind. Not to mention, South Carolina tends to have a humid environment which only exacerbates moisture issues in your crawl space.  

First, open crawl space vents allow humid air to easily get into your crawl space. When this humid air mixes with the cooler air under your home, condensation forms on the wooden structures supporting your home. Eventually, the water droplets and high moisture in the air can cause wood rot and mold to form on floor joists. These processes break down the wood and make it too weak to hold up your floors properly. Moisture can also enter your crawl space when groundwater under your home evaporates into your crawl space, and the condensation cycle repeats.  

Essentially, when water gets into your crawl space in any way, over spanned floor joists are a likely possibility. Sometimes, over spanned floor joists can simply be caused by a construction error. Floor joists work best when built close to each other; if a contractor built floor joists spread unevenly in your crawl space, they’re going to sag under the weight of your floor. Moisture issues can cause further damage in this scenario as well.  

The Risks of Over Spanned Floor Joists 

Over spanned floor joists can cause structural issues for your home and indicate larger crawl space issues. You might experience sagging floors, mold growth, or increased energy bills – all signs of excess moisture in your crawl space

Sagging Floors

When floor joists become over spanned, whether through construction errors or moisture problems, your floors will sag. This might also lead to gaps between the floorboards, and creaky floors as you walk around your home. Sagging floors pose a serious safety risk because they indicate structural problems to your property. The floor may collapse if it sags more than a few inches, placing everyone in danger. Misaligned doors and windows might also arise and can become difficult to open and close.  

mold in crawl space

Mold and Mildew

Since over spanned floor joists can be caused by moisture problems, they also imply that larger problems are present in your crawl space. Mold is one of the most common issues a wet crawl space can face. Mold spores are always present in the air, and they can enter your home as air travels up from your crawl space through a phenomenon known as the stack effect. Once inside your home, mold can begin to grow in dark and moist places such as closets, cabinets, or near plumbing lines. In addition to causing structural damage, mold can also lead to health problems, such as respiratory infections and allergic reactions.  

Increased Energy Bills

While this issue isn’t a direct result of over spanned floor joists, it is another side effect of moisture in your crawl space. Remember, moisture causes over spanned floor joists, so it can cause this issue as well. Humid air doesn’t just stay in your crawl space. Warm air always rises and will travel through your home and out through your attic in a continuous cycle known as the stack effect. As the humid air disperses throughout your home, your HVAC system will have to work overtime to maintain the temperature in your home. Eventually, your energy bills will increase, and you’ll be spending extra money.  


Floor joists are horizontal beams that span the length of your crawl space, usually and transfer the load of your floor to additional support beams around your crawl space. The weight of the walls, furniture, appliances, and people is supported by the joists and the structural integrity of walls and doors also depend on them. 

You should not try to repair your over spanned floor joists on your own. As you try to address the initial problem, you might accidentally harm other systems in your crawl space, such as piping or insulation. Your DIY attempts to “repair” your crawl space may actually make matters much worse. 

Wood rot can easily arise in South Carolina crawl spaces. You can easily identify wood rot when wood looks cracked, brittle, decayed, or spongey and soft to the touch. You might also notice a musty smell coming from the damaged wood. Wood rot is the result of excess moisture in your crawl space, and our team can help waterproof your crawl space to avoid this issue.  

Call Us For a Free Inspection! 

Over spanned floor joists can be devastating for any home if left unchecked. Not only will they cause structural issues over time, but they also suggest that moisture problems are affecting your crawl space. This can lead to pests, mold, and wood rot, among other problems.  

Thankfully, crawl space solutions exist to help you combat moisture issues. Contact us today so we can help protect your Charleston, Columbia, Greenville, or Savannah home. We’ll send a member of our expert team to evaluate your crawl space for free, and come up with the best solution for your individual needs! 

Publish Date:

Last Modified Date:

Mount Valley Service Map

Our Service Area


630 Ellis Street, Suite 2-B
Augusta, GA 30901


1850 Ashley River Rd
Charleston, SC 29407


2110 Commerce Drive
Cayce, SC 29033


300 South Ave
Spartanburg, SC 29306