And One To Grow On

I love water. I’ve got a nice glass of water on my desk right now. Without water you don’t have life in any sense that we earthlings would recognize. Unless you have a vacation home in another star system I think we can conclude that it’s pretty basic to life. And that is why it’s so important to make sure that your house stays dry.

All of the destructive and nasty effects that water cause in a building are because life is happening. Rot is simply fungi eating the wood in your house.  They need a certain moisture level in the wood to live, when the wood is below 20% moisture content rot is unlikely. Kiln dried construction lumber is usually specified as KD 19 or MC (moisture content) 19, meaning kiln dried to maximum 19% moisture content. It’s normally a little drier, because it’s still losing moisture as it is shipped and stored. Wood changes MC with relative humidity and usually ends up in a range between 9 and 15 percent MC unless you live in either Phoenix or Seattle where the range will be different.

There are two primary types of wood rot. One is a stringy growth that requires a fair amount of moisture and can be a little slimy. When a tree first falls in the forest this is often the first type of rot to show up because the wood is quite wet. The other known as brown rot or dry rot appears as brown rectangles of cracks and splits. Also the wood becomes powdery as it loses moisture. Dry rot is a bit of a misnomer, really there’s no such thing. It needs less moisture that the stringy type but still needs 25-35% MC. This type of rot will often appear on wood that is intermittently wet and dry. That might lead to some of the confusion. Often I have to explain to people that they just didn’t see it when it was wet. Finding intermittent water sources can be challenging.

So rot is caused by living things. Most of these living things are loosely classified as fungi. Mold is a kind fungi that grows as black spots near the shower and that cause the odors in your carpets. The types of fungi are truly uncounted, I’ve heard people throw numbers around like “hundreds of thousands” and “millions”. Most don’t bother us, some cause allergies, and a few will make you sick. A lot of the effect depends on concentration. The more water the more those little critters* will grow. Much of the health problem comes from the release of the spores as they reproduce.

The important point is that a wet house is an unhealthy house. Lower energy use makes dealing with water a bigger challenge so water control, for all states of water, is vital to maintain a healthy home and good indoor air quality (IAQ). We’ll be talking about how water gets in, how it moves around and other interesting things in future posts. For now, keep your powder (and your house) dry.


*If you gather a group of experts and ask whether fungi is plant or animal you better be prepared for a long listen. Some claim that fungi are an entirely separate life form.

About Buildinggeek

I love buildings. I love thinking about how they are made and how they work. I am a building geek. I love to talk about buildings too. Get in touch.
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