Do you want to know how to replace a rotten floor joist in a crawl space? Follow along! This is the article you’ve been looking for. We’re going to go over everything including why floor joists rot, how to replace them, and how to strengthen your crawl space for the future.

New deck patio with modern wooden deck installing wood floor for patio

Why Do Floor Joists Rot?

Below are four ways wood floor joists begin to rot or fail.

Wood Rot – One of the main things that affect wood is dry rot, a form of wood rot that turns joists into powder. This can cause severe structural issues if you let it take over. The fungal growth that causes dry rot begins as a spore before growing in high-humidity environments, such as the crawl space.

Then, as your floor joists soak up the excess moisture, the fungus grows white strands called hyphae before developing into mycelium, a collection of germinated hyphae. In its final stages, the fungus manifests itself as a fruiting body or a spore-producing organ of a fungus. This causes your wood beams to crack as if the beams were excessively dry, which is where the term “dry rot” stems from.

A closeup view of a man using a digital handheld moisture detector showing a moderate level of damp in wood floorboards and joists with white rot fungus.

Standing Water – Plumbing leaks and groundwater flooding can go on for weeks without you noticing it. This can lead to mold, rot, and mildew. You should check your crawl space when you can for any standing water or signs of leaks.

Grade & Gutter Issues – If you have poor grading in your yard (grading is the slope in which water drains), water can begin to pool up at your foundation or crawl space. If the downspouts from your gutters are pouring directly at the base of your home, you can be sure water is going to leak inside your crawl space. The yard should slope away from the foundation.

Pest Infestations – Many homeowners and contractors have made the mistake of removing and replacing termite or pest-damaged wood, assuming that the infestation is over because there are no visible pests. However, subterranean termites are subtle and hard-to-find creatures that can exist in a home for decades without detection. They will often abandon old tunnels and move on to new areas. In this case, replacing the damaged wood may simply be renewing its food source in your home.

3 Ways To Prevent Wood Rot

Wood rot forms from moisture in your crawl space. So the key is to eliminate the water.

Crawl Space Encapsulation – Crawl space encapsulation is when a vapor barrier is placed inside your crawl space. A vapor barrier is a thin layer of impermeable polyethylene sheeting that prevents moisture diffusion through the basement wall. This keeps humidity in your crawl space to a minimum.

Crawl space vapor barriers are the first line of defense against high humidity and poor indoor air quality. These encapsulation barriers are 10 to 20 mil thick, puncture-resistant, and made of a high tensile strength material that stops soil moisture from entering the space. These liners encapsulate the crawl space so that water cannot attack exposed wood and create mold and mildew.
Crawl space sealing prevents the humid air from settling in the space, creating condensation and promoting mold growth. Many studies have proven that a sealed crawl space creates a healthier and more energy-efficient home due to the elimination of humidity fluctuations.

Crawl space with dehumidifier and sump pump

Crawl Space Sump Pump – A sump pump is a fixture in a home’s crawl space. It helps remove groundwater from underneath your home, preventing water from seeping through your floor. Sump pumps are also used to keep basements dry. Without a sump pump (which sits in the sump “pit”), water or heavy precipitation becomes a significant issue in your home.

Dehumidifier – As a warning, you do not need a dehumidifier if your crawl space is vented. Otherwise, you will be just constantly dehumidifying outside air.

A crawlspace dehumidifier is installed in the encapsulated crawl space, positioned for optimum air circulation. Its fan circulates the clean & dry air throughout the area. This keeps crawl space humidity levels down.

How To Replace A Rotten Floor Joist In A Crawl Space

If left unrepaired, a single damaged floor joist can wreak havoc on your home’s structural integrity. However, the damaged joist can be reinforced by placing another “sister” beam alongside it. This is called sistering a joist. Also, completely removing and replacing the damaged wood member may be necessary.

We do not recommend trying to remove and replace the rotten floor joist yourself. Once you identify the problem, or if you want to call professionals to find the problem, you can be sure that highly-trained contractors will do the best job possible.

foundation construction

How To Strengthen Your Crawl Space

Lucky for you, reinforcing a weakened crawl space is more manageable than other structural problems. Using steel crawl space jacks and steel posts on a concrete foundation or pad, you can lift a weak joist and or beam back into place. Crawl space jacks have an ultimate capacity of 60,000 lbs. Again, if the floor joist or support beam is too damaged, a sister joist or full replacement may be necessary. Also, concentric steel brackets and piers can be advanced through any unsuitable soil condition for a stabilized and permanent lifetime repair.

Crawl space jacks in a crawl space.

Who Can Help You Replace A Rotten Floor Joist In A Crawl Space

If you are having issues with your floor joists or crawl space, who should you call for help? Check out Foundation Professionals of Florida, an award-winning and top-performing company. We specialize in all your crawl space, foundation, and slab repair needs and can provide any of the services above. Click here for more information and contact us today.