Wood Decay

Dry rot can be a big problem for both new and experienced homeowners but particularly plagues those of us who live in the often damp Pacific Northwest. Despite its colloquial name, ‘dry rot’ is most often caused by communities of fungi growing in wood with high moisture saturation. Understanding how and where rot takes hold can help property owners recognize and minimize future damage to their homes.

Two types of cellulose-eating fungi account for most of the damage described as dry rot. Brown rot turns lumber made from pine and fir trees into blocky, cracked wood. White rot, which affects mostly hardwoods, turns solid wood into splintery pulp by breaking down both cellulose and lignin.

Most fungi need water, food, oxygen, and temperatures above about 40°F. If we can take just one of these factors away, we can significantly affect the ability of white and brown rot to grow.

In the eyes of the rots (yes, personification) wood is food. The same rigid sugars and proteins in trees that we use to build structures are a convenient and abundant source of energy for microscopic organisms. We can treat wood with chemicals and sealants to make it less appealing to the rots, but treated wood can be costly.

Lumber far enough below ground is usually safe from dry rot, but unless you’re Bilbo Baggins it is pretty hard to keep oxygen from surrounding your structure. Temperatures in Portland are pretty consistent too, so temperature control might also be out when it comes to tackling dry rot.

Luckily, the construction industry has spent the last century honing weatherization products. From high tech water resistive barriers to long lasting calking and siding there is a weatherization solution for every house. Check out more on the life cycle of rot in Fine Homebuilding’s howitworks article.