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Everything You Need to Know About Moisture Content of Wood

If you want to make sure that moisture will not affect your upcoming project, this guide is for you. We will break down everything you could possibly want to know about the moisture content of wood.

How Does Moisture Affect Wood?

Wood is hygroscopic. What does that mean? Moisture influences the strength of the wood. When the moisture content of the wood increases, this expands the wood. As humidity decreases, so does the moisture, shrinking the wood. This is known as EMC, or equilibrium moisture content. If you install recently-moved wood or work with wood installed on the job, it may take some time for the material to reach EMC with the air. If wood is at 10% and exposed to humidity at 25%, it will dry to 5% and shrink as a result.


How To Calculate Moisture Content Of Wood

The average moisture content of wood can easily be determined using the dry weight method. You can also use a moisture meter. If you’re using a meter, the resistance should have some hammer electrodes and insulated probes.

Average Moisture Content Of Wood

The standard moisture content of wood stands between 8% and 25% by weight. The EMC of the wood corresponds to the air temperature and the relative moisture.


Wood being air dried before kiln drying.

Moisture Content Of Kiln Dried Wood

Kiln-dried wood usually shows a moisture reading of 10% on the outside and then 25% on the inside. The moisture content overall is almost always below 20%. Logs, siding, shiplap, and T&G must be kiln-dried to stop the wood from shrinking or pulling apart.

Post and beam constructions don’t have to be kiln-dried but should be air-dried. Post and beam constructions don’t have the same risk of separation in the same way T&G does. Most post and beam structures are outside as well, and this makes it easier to acclimate. If you are using post and beam indoors, you need to make sure that it is as dry as possible to avoid shrinkage and eventual separation. We always choose 20% moisture for anything indoors and 30% or less for outdoors.

Acceptable Moisture Levels In Wood

Moisture levels between 9-14% for anything outdoors. Anything under a 30% moisture level is generally acceptable, depending on the application.

Why Is Wood Moisture Content So Important?

Moisture content is essential in wood because it can cause the wood to shrink and then expand. There will always be seasonal changes, but you can be sure to get the best result in no time by choosing a wood with good moisture content.

How Do You Control Moisture In Timber?

Air drying is the best way to control moisture in timber. Storing any sawn timber in a clean and dry area or stacking it on raised foundations will allow nature to take its course. The wood will eventually adopt the same moisture level as the air around it.

What Is The Required Moisture Content Of Structural Wood In Residential Construction?

Structural timber needs to be around 20% or less when it comes to structural work.

How To Store And Dry Your Timbers

If you want to store timber, you have to make sure that you do so on a raised platform. You have to make sure that the wood has room to breathe, and you also need to make sure that you allow it to adapt to the environment. If you store your wood in a humid climate, the humidity of the wood will increase, so you have to make sure that you allow for this when working with it. One way to ensure a positive result with the wood you are using would be to store it on-site for a few days before you start the project.

If you want to make sure that you are getting the best result out of your wood, Western Red Cedar is usually a good option. It can be delivered at around 12% moisture content, and it’s suited to indoor and outdoor applications.

Moisture Content of Wood Chart

Humidity of the in-use
EMC of the in-use location Corresponding MC the wood will attain at this location
19-25% 5% 5%
26-32% 6% 6%
33-39% 7% 7%
40-46% 8% 8%
47-52% 9% 9%

Contact Us

We know how important it is for you to find wood with the right level of moisture content. We also know that finding a good supplier can be difficult, and that’s why we make it easier for you. Here at Reliance Timber, we make sure that the wood we source is the proper moisture content, and we can also make sure that the wood you are choosing is the best type for your project. If you want to get in touch with us, the only thing you need to do is give us a call at 828-264-6680.