Wood rot is a commonly used term in the Real Estate and Inspection world refers to decayed and damaged wood. Wood decay is caused by a species of fungi feeding or consuming the cellulose and lignin that compose the wood cell walls. These fungi secrete enzymes which help dissolve the wood cells and change its form so it can be absorbed by the fungi. There is no reversing wood rot. Like other microbial growth, they reproduce and spread microscopic spores which can lay dormant for long periods of time until the right conditions present themselves. These woods destroying organisms need just three things to survive; air, water and food. Since we can’t do anything about the air, and our homes are made of wood (their food) that leaves controlling water and moisture as our only option for preventing wood rot. As a state licensed Home Inspector, I am not concerned with identifying which species of fungi is at work when wood rot is found, but I am concerned with the moisture source and how wide spread the damaged area is.

Identifying the moisture source

Determining where the water source is coming from is often the easiest part, as it is most likely either from rainfall or a plumbing leak. Every now and then though there is a 3rd way liquid water can appear and be the moisture source and thus cause of wood rot, and that is from condensation forming. When warm humid air comes into contact with a hard surface or vapor barrier and its temperature is below the dew point, liquid water will form. This can be demonstrated by putting a cold beverage in a can or glass container outside on a hot day. The condensation will keep occurring until the beverage warms up past the dew point. If you have HVAC ducts or equipment that isn’t properly insulated, condensation will form and will keep forming as long as that surface is below the dewpoint temperature. Here in North Florida during the summer months our dew point can be in the mid to upper 70’s. Wood rot from condensation will take longer to occur in general but I have seen some extreme cases while performing home inspections here in North Florida. In the coming months there will be another blog post where we will discuss in greater detail the relationship between air temperature, humidity and dew point.

Finding the damaged areas

I do my best to try and identify the areas of wood rot or concern, but determining the full extent of the wood rot isn’t the job of a home inspector, as we can’t remove materials or open up walls. Unfortunately, there are times where you can’t see the wood rot. An experienced home inspector knows that sometimes wood rot isn’t readily visible and can be concealed with a fresh coat of paint, so probing the wood is needed at times. The state of Florida recognizes this and outlines it the Standards of Practice for Home Inspections by stating, “(2) The inspector shall inspect all of the visible structural systems and components by probing structural components where deterioration is visible or suspected or where clear indications of possible deterioration exist. Probing is not required when, in the opinion of the inspector, probing would only further damage any area already identified as defective or where no deterioration is visible or presumed to exist.” Probing is done with a small hand tool such as a screw driver or awl and won’t damage or harm healthy wood. For lack of a better explanation probing is just poking the wood surface with minimal force to see if the wood is still structurally sound. Anyone that has ever hammered a framing nail knows that it takes a bit of force to drive that nail into the wood. If the probe goes into the wood then the wood was already damaged from wood rot and probing just uncovered it. Sometime the probe just goes part way in showing that there is still some structural soundness left in the wood.

Preventing Wood Rot

As discussed earlier, since the fungal spores are ever present, there are generally two approaches to keeping wood rot from occurring. The first is to keep the wood dry enough that fungal growth can’t occur. This is the goal of paints, stains, and sealers. These finishes will help keep the moisture content of the wood below a level where growth occurs. The second is to make the wood to toxic for the fungi to thrive. A common example of this would include pressure treated wood, the issue with this approach is the same chemicals are also toxic to humans and should be used carefully and not indoors. BORA-CARE is one product that can be applied in the field to wood to help control fungi and insects.


Some obvious wood rot and staining to the subflooring and joists along with substandard repairs seen in a crawlspace in a Tallahassee home.

Inspection of a crawl space revealed wood rot in the subfloor around a toilet.

The wood rot shown here is most likely from a poorly seated toilet. Anytime there is a loose toilet, the toilet should be pulled and the subfloor checked to make sure damage isn’t present.

During a home inspection in Tallahassee, an inspectors probe goes through T111 siding, indicating presence of wood rot.

Even though this siding looks to be in good shape, you can see the probe goes right through the T111, indicating to the inspector that there is wood rot.

Another Tallahassee Home Inspection uncovers wood rot in a home's siding while probing.

The siding looked a little more suspect in this area, but you can see with probing, the wood rot was evident.

The corner of a wood soffit is a likely spot to find wood rot during a home inspection.

The corner of a wood soffit is a likely place to find wood rot. In this picture you can see the probe easily goes into the wood, indicating damaged wood and rot.

A tallahassee home inspector finds wood rot in the sheathing behind exterior siding.

This sheathing has water damage and wood rot which was visible in the attic, but could not be seen from the exterior.

Exterior view of a roof to wall intersection where kick out flashing was needed, discussed in a home inspection report.

This roof to wall intersection was missing kick-out-flashing, which could have prevented the wood rot found in the attic. You cannot tell there is anything wrong with the sheathing underneath the siding from this vantage point.

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