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  • Writer's pictureKevin Peterson

Dry Rot Demystified: A Must-Read Guide for SF Bay Area Homeowners

Updated: Mar 29

In the SF Bay Area, nine out of ten home / pest control inspections denote dry rot. This article answers seven critical questions that every homeowner should know about dry rot.



  • Dry rot is a fungus that attacks wood and destroys cellulose, leaving wood weak and brittle.

  • Left untreated, it can spread throughout your home, compromising the structural integrity.

  • Regular inspection and early detection are key to preventing dry rot.


FAQ of Dry Rot


1. Where Does Dry Rot Occur and How to Identify?

Dry rot may sound as though it’s misnamed because fungus (aka “Serpula lacrymans”) needs moisture to grow. In fact, all it needs is an average humidity level above 30%. The other three ingredients for this fungus to be present are:

  • Wood

  • Oxygen

  • Warmth (temps between 71 and 77 degrees)

Once rot starts growing, it spreads rapidly. Dry rot affects wood and can travel through various materials, including masonry. If not stopped, dry rot will weaken an entire building to the point of decay. Dry rot can start anywhere (e.g. trim around windows, floor, ceiling beams) and lead to severe structural problems, including deteriorated support posts and beams. 

If you see any of these signs in your home, you probably have dry rot.

  • Visible fungal growth that looks like a fluffy white cobweb

  • Strained drywall

  • Water droplets on the surface of the wood

  • Brown dark timber

  • Brittle or weak wood

  • A musty or damp smell

  • Patches of light purple, orange, or brown that peels easily

  • Grayish strands on the wood or timber

  • Fruiting mushroom bodies among the spores

Outside, areas to look for dry rot include:

  • Damaged gutters or downspouts

  • Wooden window sills.

  • Where water runs off the roof along a wall.

  • Where a deck attaches to the home.

  • Where a vertical surface meets a horizontal surface.

  • Look for cracking, splits, and discoloration, which may indicate the presence of rot. Check the roof, especially areas where your home may have had a leak. Dry rot can also occur at points of a structure where wood meets the ground.

Inside, look for dry rot in areas where there may be a leaky pipe, unvented attic space, and damp basements or crawlspaces. Other areas to check include:

  • Rim joists, especially on a porch, crawlspace or basement.

  • Where wood meets a masonry floor or wall.

  • The floor around a tub or toilet.


2. How Can the Average Homeowner Check for Dry Rot?

To identify if there is dry rot, you have three options, from cheapest to most expensive.

  • Option 1: Visual inspections as noted above

  • Option 2: Push on it by using a pick or screw driver; if it penetrates the wood or the wood flakes easily, there is rot. Another option for flooring, or siding could be to apply weight or pressure to see if it feels structurally sound.

  • Option3: Call a home inspector 


3. How Dangerous is Dry Rot?

While dry rot spores are not harmful themselves, a house with dry rot isn't a pleasant place to live in, especially with the smell of damp soil filling the air. The damp conditions pose a health hazard for infants, older people, and those with respiratory diseases.

Beyond this, dry rot is very dangerous to your home itself and should be treated before it becomes an issue.


4. How to Triage?

Now that you know you have dry rot, what do you do to treat it? 


Dry rot is progressive so you will want to make repairs as soon as possible. If you find dry rot, you will first need to stop the source of the moisture. Replace wood that has been structurally weakened, possibly with pressure treated wood. Be sure the problem is properly diagnosed and not mistaken for damage done by carpenter ants.

Once you have found the source of moisture, repair the problem. If there is severe damage, pry off and replace the old wood. Be sure to temporarily support any structure before removing the old wood. Small areas of rot can be repaired with epoxy resin. If the wood is still structurally sound and the source of the moisture has been stopped, you can treat the area with borate, a fungicide, to stop the growth of the fungus and protect the wood from further damage.

Most importantly, treat dry rot as soon as it is discovered! Untreated dry rot can cause major damage to your home.


5. How to Prevent?

To prevent dry rot, there are several things you can do around your house as preventative maintenance. 

Create a routine - Inspect your home exterior at least twice a year as well as after severe storms. Don’t procrastinate home exterior maintenance, or problems could get worse and more costly.

Ensure the following:

  1. Properly ventilate and insulate your attic.

  2. Properly ventilate crawlspaces.

  3. Seal basement and crawlspace floors to reduce ground moisture.

  4. Check all wall and roof flashing to ensure water is being directed properly.

  5. Check deck and porch flashings.

  6. Keep wood siding and trims off the ground and away from the roof and masonry.

  7. If you see wood on your home exterior become exposed, if your caulking starts to crack, or your paint begins to peel, it is wise to promptly fix the problems to avoid wood rot.

  8. Make sure all windows and doors are properly flashed.

  9. Keep up on painting and caulking.

  10. Keep drains and downspouts clear - If your gutters begin to leak, fix them promptly

  11. If there is considerable runoff near the house, consider installing a rain barrel to collect water or connecting your downspout to a drainage pipe that can move water a safe distance from your home.


6. Is Dry Rot Covered by Home Insurance?

Usually, dry rot is not covered by insurance. However, most homeowners insurance policies offer coverage for sudden or accidental water damage, which might be the direct cause of your dry rot. If a pipe bursts and subsequently causes water damage which develops into dry rot, your insurance may cover at least a portion of these repairs. 

Any additional dry rot or fungal growth that occurs over a longer period would not be covered.

Most home insurance policies don’t include coverage for floor damage either, so if you live in an area prone to flooding, consider purchasing a flood damage policy.


7. How Much to Repair?

In minor fungus infections, the area can be scraped out and treated with a fungicide (Boracare), then filled and painted to protect the area. This typically is in the ballpark of a few hundred dollars. 

In more severe situations, the damage needs to be replaced and the surrounding area should be treated with a fungicide. If in the exterior and easily replaceable, could be a few hundred to a few thousand dollars. If in structurally important areas, the cost to repair could be extensive.

Again - The most important factor in dealing with fungus is to cut off the moisture source.  After areas have been repaired or replaced, the area must be protected.  Caulking end cuts or seams and painting is crucial.


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