How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manufactured and modular homes

Does wood rot spread? Is it contagious?

Tuesday, August 14, 2018

Wood rot is definitely contagious under certain conditions. But, once you understand that wood rot is a type of fungus—along with the mechanism that the fungus uses to spread and the conditions necessary for it to infect an area of wood—then your diligent maintenance will stop rot from appearing at new areas of wood.

   Here’s are our “Three Rules of Wood Rot”:

1) Existing wood rot fungus colonies are constantly sending our spores into the air. These spores are floating around pretty much everywhere in the wind. It’s not necessary to have an area of wood rot nearby for spores to land on an exposed surface of wood. There are likely already plenty of wood rot spores on the surface of any wood exposed to outdoor, unfiltered air.

 2) Moisture is necessary for the spores to begin growth. It can either be in the form of extremely high humidity that raises the moisture content of the wood over time (in a poorly ventilated crawl space under an elevated wood floor, for example), or lumber that has not been sufficiently kiln-dried at the factory to reduce the moisture content to under 20%, or water soaking into the wood surface that does not naturally drain by gravity and allows water to puddle on it.

 3) Warm air temperature is also necessary for wood rot to flourish, although it possible for it to grow at temperatures down to nearly freezing. 

  While warm temperature is a component, the main trigger for wood rot to begin is moisture in the wood. The number one type of defect we see that causes rot at exterior wood siding and trim is any surface that allows rain water to puddle on the wood without draining or to seep into any any openings between pieces of wood. This is called a “water trap” by builders, and a good craftsman works to make sure than any horizontal surfaces, such as window sills, have a slight slope to the outside so that no water puddling occurs, along with carefully caulking around windows and trim to seal out wind-blown rain out. Maintaining paint as a barrier on the surface of the wood is also important.

   If you find areas of wood rot on the exterior of your home, be sure to repair the area in such a way to eliminate any future water traps. Also, rot at the bottom of plywood exterior siding is often due to splash-back of rain water off the ground from a roof overhang above. The worst location for splash-back areas of rot is where the roof drains onto a patio or driveway, and the best preventive measure is to install a gutter system over the area.

   Another location where wood rot can develop is in the attic at leaking roof penetrations, such as in the photo at the top of the page of the roof sheathing below a leaky chimney flashing.  Landscape sprinklers that regularly spray on the wood trim of a house can also accelerate rot, like in the photo below.

     To learn about how an inspector looks for wood rot, go to our blog How does a home inspector evaluate wood rot?

• • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Here’s links to a collection of our other blog posts about WOOD ROT:

Where are the most common places to find wood rot on a house?

How do I treat wood rot  that's listed in my termite-WDO report? 

What causes wood rot on a home?

Why is the inspector calling out rotten wood on my termite inspection? 

• Is wood rot found on a home inspection considered serious? 

Is wood-decay fungi found during a termite (WDO) inspection the same as mold?

        Visit our TERMITES, WOOD ROT AND PESTS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles. 

Water Heaters

Water Heater Age

"What Are The

Signs Of..."

Septic Tank Systems

Structure and Rooms

Plumbing Pipes

Termites, Wood Rot

& Pests



When It First

Became Code

"Should I Buy A..."

Park Model Homes


Shingle Roofs




Wind Mitigation

Roof and Attic

"Does A Home


Pool and Spa

"What Is The Difference Between..."




Concrete and

Concrete Block

Metal Roofs


Modular Homes

Rain Gutters

Mold, Lead & Other Contaminants


Older and

Historic Houses

Crawl Spaces

Mobile-Manufactured Homes

Building Permits

Life Expectancy

Clay Soil





Exterior Walls

& Structures


Common Problems

HUD-Code for

Mobile Homes

Garages and Carports

Flat (Low Slope) Roofs

Electrical Panels

Sprinkler Systems

Electrical Receptacle Outlets

4-Point Inspections

Hurricane Resistance

Frequently Asked Questions (FAQ)

Home Inspection

Heating and Air Conditioning

Building Codes

Fireplaces and Chimneys

Inspector Licensing

& Standards

Energy Efficiency

Washers and Dryers



Doors and Windows



Electrical Wiring

Click Below  

for Links

to Collections

of Blog Posts

by Subject

Plumbing Drains

and Traps


Smoke & CO Alarms

Aging in Place

Top 5 results given instantly.

Click on magnifying glass

for all search results.






Air Conditioner & Furnace Age/Size


Electrical Switches





Water Intrusion

Electrical - Old

and Obsolete


Foundation Certifications

Tiny Houses

About McGarry and Madsen



Buying a home in North/Central Florida? Check our price for a  team inspection by two FL-licensed contractors and inspectors. Over 8,500 inspections completed in 20+ years. In a hurry? We will get it done for you.

Moisture Problems

Crawl Spaces