Floor joists are one of the most important structural features of any home. They are the timber beam that runs perpendicular to the supporting beams and parallel to the wall. Joists provide a supportive framework for flooring. In short, they’re literally the ground beneath your feet.

To maintain their structure, floor joists must be able to carry the dead load of furniture, the vibration of people, impact loads, and the flooring load. It’s a lot of weight and pressure. That’s why floor joists use high-quality timber to provide durability, evenness, and strength.

Given their importance in the integrity of your home, water damage to floor joists is more than a homeowners’ nightmare – it’s potentially catastrophic. Moreover, because they’re hidden away in the bowels of the house, most homeowners do not spot water damage until the joists are rotten or failing.

Learning how to repair floor joists with water damage is essential to protecting your property. You’ll want to identify the early signs of rot, know the common causes of rotten floor joists, and know how to repair or replace the rotten joists.

Read on to find out more.

How to Identify a Rotten Floor Joist

The best way to identify water damage in a floor joist is to conduct a visual inspection. There is no substitute for looking at the joint itself. However, when floors, ceilings, or crawlspaces cover a joist, that can be challenging. In such cases, you need to spot the telltale signs of damage.

Here are some of the most common signs to look for:

• Uneven or sagging flooring
• Cracked doors or windows
• Mold, allergens, or odors near the floor
• Staining on floors or ceilings
• High levels of condensation in your home
• Termite or pest issues

Floor joists are affected by two different kinds of rot:

Wet rot occurs due to fungus growth after the wood is saturated with water. Causes include flooding or a serious plumbing leak. You’ll spot a dark brown color on the joist, soft and crumbly wood, and possible black fungus growth.

Dry rot, on the other hand, occurs due to high moisture levels. In these conditions, the fungus takes longer to grow – causes include high levels of condensation, moisture build-up, or poor ventilation. Dry rot is a major concern, as it can spread to other wood, even crossing brick and mortar surfaces. Look for white fuzzy mold, brittle wood, and a high level of interior condensation on walls or windows.

Common Causes of a Rotten Floor Joist

There are four primary reasons for rotten floor joists:

1. Water leaks or flooding. Damage to pipes and flooding is the primary cause of rotten joists. The damage is less likely when the wood is left to dry out quickly. However, if prolonged, mold will set in.
2. Moisture build-up. Condensation and moisture are natural within certain limits. Poor ventilation, however, causes high levels of moisture that lead to significant water damage.
3. Horizontal penetration. If water is seeping through foundation walls or runners, it’s called horizontal or sideways penetration. It causes the joists to rot from the ends inward.
4. Rising damp. In older homes with stone or brick/mortar foundations, water can flow upwards through the foundations into floor joists and walls.

How to Repair Floor Joists with Water Damage

To repair or replace, that is the question. As a rule of thumb, many professionals say if the rotten area is larger than six inches across, you should replace the joist or “sister” it from end-to-end. If multiple joists are affected, it almost always involves replacing the affected joists.

That’s not to say repairing joists is never appropriate. Consider performing a DIY repair of a joist if:

• The joist is not supporting a load-bearing internal wall
• The rot infestation is restricted to a single joist or specific location
• You can access both ends of the joist without affecting the structural integrity
• You have the tools, knowledge, and experience to complete the job.

If the answer is no, speak to a professional like United Restoration – we’re more than happy to evaluate and repair any joists damaged due to water.

Here’s how to replace a joist with water damage:

• Stop the moisture or water. You cannot fix an ongoing problem. Find the source of the moisture or water and ensure it has stopped.

• Access the joist. The best option is to access a joist from the basement or crawlspace. That means you don’t have to damage expensive flooring or the subfloor’s integrity. Otherwise, you’ll need to remove the flooring to access the joist from above or remove the ceiling to access the joist from below.

• Install a temporary beam. If one or more joists need repairing, you’ll need to use two or more floor jacks to help install a temporary beam to support the floor during repairs. If necessary, nail the beam to the underside of the floor joists for extra safety and stability.

• Sister the joist. You need a piece of timber of similar size, type, and dimensions. Cut it to length to ensure sufficient overlap with the non-rotten part – longer is better. Bolt the sister joist into place (use heavy structural steel carriage bolts for the most security).

• Remove or replace the rotten section. You won’t always need to remove the rotten part if the infestation has been thoroughly dealt with. However, make two vertical cuts in the joist for severe rot and use a pry bar to separate the rotten section from the subfloor. Pull it loose and replace it with a section of lumber similar in dimensions and type. Use structural steel plates to bolt the new section into place.

That’s how to repair a water-damaged floor joist. We advise always contacting a professional for such serious repairs. Contact United Restoration today, and we’ll evaluate the repairs you need.