Relative Humidity: Wood and People

Relative Humidity: Wood and People

Hundred degree temperatures are not always equal. Have you ever been to Las Vegas in the summer? Everyone says that the temperature is 100 degrees but it is a dry heat so it’s not as bad. But head down to the Gulf of Mexico and that hundred degrees will be much different. What is the difference? It’s humidity.

Humidity is the amount of water vapor in the air divided by the amount of dry air at any given temperature and is known as the absolute humidity. The hotter the air, the more water it can contain. What we all feel is the relative humidity, which is the ratio of the current absolute humidity to the highest possible absolute humidity. A 100% reading means that the air is completely saturated and at cloud level means rain clouds will form and stormy weather is on the way. So when your weatherman says the humidity is 80% that means that 80% of the air is saturated.

Relative humidity is a ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. The relative humidity can rise as the temperature falls and vice versa.

We are sensitive to relative humidity. When we sweat we depend on that sweat to evaporate in the air to keep us cool but with a higher relative humidity the sweat will not evaporate and the air will feel hotter than it actually is. This also works the other way around as at cooler temperatures sweat will evaporate quicker giving us a cooler feeling. If you are interested humans are most comfortable at around 45% relative humidity. So there, the next time your local weatherman pops the graphic up that says what the temperature feels like you know what goes into that. Maybe you can even steal their job!

Humans are not the only things that deal with humidity. Wood does as well. The equilibrium moisture content (EMC) is the level at which wood neither gains nor loses moisture and when this point is reached a piece of wood is acclimated to its environment and ready to use. It can take time for wood to reach the EMC as the relative humidity varies across the world. Arid environments means the wood needs to lose moisture and in more tropical environments it needs to gain moisture. This is sometimes known as breathing.

Why is this important? If you were to spend your hard earned money to purchase a reclaimed hardwood floor from Aged Woods you would want it to be installed correctly and stay that way wouldn’t you? If the wood is not given time to reach its EMC it will probably cup or warp over time leaving you with a disaster on your hands. So, how can you tell? Moisture meters are used to measure the moisture so that you will know when your reclaimed wood reaches its EMC and is ready to be installed. After that, your home may need de-humidifiers or humidifiers (in the summer and/or winter respectively) to keep the RH at a comfortable level. The additional benefit is that if the wood is comfortable, so will people.

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