Does Wood Shrink In Cold Weather?

For those of you who were fans of Seinfeld (I am one), perhaps you remember the episode when the four stars went to the shore, spending the weekend both swimming and sunbathing.

Kramer stole lobsters while Jerry and George went to a farmer’s market to shop for tomatoes.  That’s not the funny part, though.

Key Points:

  • Temperature alone does not cause wood to shrink.  The humidity level inside the wood plays a greater role in shrinkage than temperature.
  • Temperature determines, to a great extent, the amount of moisture wood can absorb; warmer air can hold more moisture than colder air, and the increased surrounding humidity level gives wood more moisture to absorb. Conversely, cold air holds less moisture, there is less for the wood to absorb, and wood contracts.
  • Temperature changes do cause wood movement, and allowing for expansion and contraction in some of your projects can be important (think wood floors, for instance); but it’s the humidity level in the surrounding environment and internal humidity level of the wood that leads to shrinkage and expansion.

George had been in the cold water and returned to his room to change clothes.  Elaine walked in while George was changing, and, well, you guessed it.

George wasn’t upset because he was caught naked; he became upset because of what he referred to as the “shrinking” effect caused by swimming in cold water.

I know this doesn’t have anything to do with woodworking, but it does have to do with shrinking and cold.  Just as the cold water caused “shrinkage” for George, so does cold and water (moisture) precipitate shrinkage in wood.

Let’s examine this a bit more closely to understand.

Does Temperature Affect Wood, and If So, How?

Temperature affects wood indirectly through its effect on moisture content. Wood is hygroscopic, meaning it absorbs and releases moisture from the surrounding air. As the temperature of wood changes, so does its moisture content.

This is because the amount of moisture that wood can hold decreases as the temperature increases.

When wood absorbs moisture, it swells. When wood loses moisture, it shrinks. The amount of swelling or shrinking that occurs depends on the type of wood, its species, and the amount of moisture it contains.

For example, hardwoods typically swell and shrink more than softwoods.

Warmer temperatures can cause wood to expand and warp. This is because the wood fibers expand more in the direction of the grain than across the grain. This can cause boards to cup, bow, or twist.

Cold temperatures can also cause wood to shrink and crack. This is because the wood fibers contract more in the direction of the grain than across the grain. This can cause boards to split or check.

To prevent wood from warping or cracking due to temperature changes, it is important to store it in a cool, dry place. You can also seal the wood with a finish to help protect it from moisture.

Here are some additional tips for protecting wood from temperature changes:

  • Use a moisture meter to check the moisture content of wood before you use it.
  • If the moisture content is too high, let the wood dry out before using it.
  • Install wood in a way that allows for expansion and contraction.
  • Use a finish that will protect wood from moisture.
  • Always store wood in a cool, dry place.

How Does Moisture Affect Wood?

Wet Wood

Moisture affects wood in a number of ways, including:

  • Swelling and shrinking: Wood absorbs and releases moisture from the surrounding air. As the moisture content of wood changes, so does its size. The absorption of moisture will cause wood to swell while losing moisture will cause wood to shrink.  This can cause problems with wood furniture and other wooden objects, as they may warp, cup, or crack as they dry or swell.
  • Strength and durability: Wood that is too wet or too dry is weaker and less durable than wood that has a moisture content in the range of 6-12%. This is because the moisture content affects the way that the wood fibers bond together. Wet wood is more likely to warp, split, or crack, while wood that is too dry is more likely to shrink and crack.
  • Decay and rot: Wood that is exposed to moisture for long periods of time is more likely to decay or rot. This is because moisture provides a favorable environment for the growth of mold, mildew, and other microorganisms that can damage wood.
  • Warping and cracking: Wood that is exposed to uneven moisture levels can warp and crack. This is because the different parts of the wood will absorb or release moisture at different rates, and the expansion and contraction of wood will be uneven.

To protect wood from moisture damage, it is important to store it in a cool, dry place. You can also seal the wood with a finish that will protect it from moisture. If wood does become wet, it is important to dry it out as soon as possible.

What Is Potential Expansion and Contraction In Wood?

Weathered Wood Cracking

Wood is a hygroscopic material, as we mentioned earlier, which means it absorbs and releases moisture from the surrounding air. As the moisture content of wood changes, so does its size.

Moisture absorption leads to swelling while losing moisture will lead to shrinkage. The amount of expansion and contraction that occurs depends on the type of wood, its species, and the amount of moisture it contains.

The potential for expansion and contraction of wood can be substantial and does require some planning.

For example, a board of oak that is 12 inches long and has a moisture content of 10% will expand by about 1/16 of an inch if the moisture content increases to 12%. This may not seem like much, but it can be enough to cause problems with wood furniture and other wooden objects.

The potential expansion and contraction of wood is greatest across the grain, which means that boards will tend to cup or warp as they dry or swell. To prevent this, it is important to install wood in a way that allows for expansion and contraction.\

This can be done by using a technique called “kerfing,” which involves cutting thin slots into the back of a board. The slots allow the wood to expand and contract without warping.

Another way to prevent wood from warping is to use a finish that will protect it from moisture. A good finish will seal the wood and prevent it from absorbing moisture from the air.

As we said, it is also important to store wood in a cool, dry place. This will help to prevent the wood from absorbing moisture and swelling.

Does Cold Weather Harm Wood?

Wooden Bench In Snow

I suppose we should ask ourselves if our outdoor wood furniture should come in for the winter months.  It’s a fair question, and the answer depends on whether cold weather will affect the wood.  We know how the winter months affect us.

Cold weather can cause harm to wooden furniture. Wood absorbs and releases moisture from the surrounding air. As the temperature of wood changes, so does its moisture content. This is because the amount of moisture that wood can hold decreases as the temperature increases.

When wood absorbs moisture, it swells. When wood loses moisture, it shrinks. The amount of swelling or shrinking that occurs depends on the type of wood, its species, and the amount of moisture it contains. For example, hardwoods typically swell and shrink more than softwoods.

Cold weather can cause wood furniture to shrink and warp. This is because the wood fibers contract more in the direction of the grain than across the grain. This can cause boards to split or check.

If wood furniture is exposed to cold weather for a long period of time, it can become brittle and weak. This is because the cold weather causes the wood fibers to become more rigid and less flexible. Brittle wood is more likely to crack or break when it is subjected to stress.

To protect wood furniture from cold weather damage, it is important to store it in a cool, dry place. You can also seal the furniture with a finish that will protect it from moisture. If wood furniture does become wet in cold weather, it is important to dry it out as soon as possible.

Is It Temperature or Moisture Content That Can Harm Wood?

Wooden Deck In Rain

We’ve suggested that both temperature and moisture content can cause shrinkage in wood, and we know that cold temperatures can harm wood.  What about warm temperatures?  What about the humidity level of the environment where the wood is used/stored?  

We know that “cured” wood, wood that has been allowed to dry after cutting, will reach an internal humidity level consistent with the humidity level of its surrounding environment.  This is referred to as equilibrium moisture content.  

Equilibrium moisture content (EMC) is the point at which a material stops absorbing or releasing moisture to reach a balance with the humidity in its immediate environment. The value of the EMC depends on the material and the relative humidity and temperature of the air with which it is in contact.

For example, woods that are used indoors have an EMC of 8% to 14% moisture content. If wood is used outdoors, then its EMC is approximately at around 12% to 18%.

Both temperature and moisture content can harm wood. Wood absorbs and releases moisture from the surrounding air. As the temperature of wood changes, so does its moisture content. 

When wood absorbs moisture, it swells. When wood loses moisture, it shrinks. The amount of swelling or shrinking that occurs depends on the type of wood, its species, and the amount of moisture it contains.

For example, hardwoods typically swell and shrink more than softwoods.

  • High moisture content can cause wood to swell and warp. This is because the wood fibers expand more in the direction of the grain than across the grain. This can cause boards to cup, bow, or twist.
  • Low moisture content can cause wood shrinkage and cracking. This is because the wood fibers contract more in the direction of the grain than across the grain. This can cause boards to split or check.
  • Extreme temperatures can also damage wood. Cold weather can cause wood to shrink and crack, while hot weather can cause wood to swell and warp.

The ideal moisture content for wood furniture is typically between 6-8%. If the moisture content is too high or too low, it can cause the furniture to warp, crack, or split.

To protect wood furniture from moisture damage, it is important to store it in a cool, dry place. You can also seal the furniture with a finish that will protect it from moisture. If wood furniture does become wet, it is important to dry it out as soon as possible.

Here are some additional tips for protecting wood furniture from moisture damage:

  • Use a moisture meter to check the moisture content of wooden furniture before you store it. If the moisture content is too high, let the furniture dry out before storing it.
  • Install wood furniture in a way that allows for expansion and contraction. This can be done by using a technique called “kerfing,” which involves cutting thin slots into the back of a board. The slots allow the wood to expand and contract without warping.
  • Use a finish that will protect wooden furniture from moisture. A good finish will seal the furniture and prevent it from absorbing moisture from the air.
  • Store wooden furniture in a cool, dry place. This will help to prevent the furniture from absorbing moisture and swelling.
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If you live in an area with cold winters, it is a good idea to bring your wooden furniture indoors during the cold months.

This will help to protect it from the cold weather and prevent it from being damaged. Weather conditions, both the warm weather and the winter weather, can cause damage to wood.

Do Hardwoods Shrink and Swell More than Softwoods?

Yes, hardwoods typically shrink and swell more than softwoods.

This is because hardwoods have a higher density than softwoods. Density is the amount of mass per unit volume of a material. The higher the density, the more moisture the wood can hold.

When wood absorbs moisture, it swells. When wood loses moisture, it shrinks. The amount of swelling or shrinking that occurs depends on the type of wood, its species, and the amount of moisture it contains.

For example, oak, maple, and mahogany are all hardwoods that shrink and swell more than pine, fir, and spruce, which are all softwoods.

The difference in shrinkage and swelling between hardwoods and softwoods is due to the cell structure of the wood. Hardwoods have a larger cell structure than softwoods. This means that there is more space for moisture to be absorbed and released.

The higher shrinkage and swelling of hardwoods can be a problem in some applications.

For example, hardwood flooring may cup or warp if it is not properly installed. However, the higher density of hardwoods also makes them stronger and more durable than softwoods. This makes them a good choice for furniture and other applications where strength and durability are important.

Here are some examples of hardwoods and softwoods and their shrinkage rates:

HardwoodShrinkage (%)
Oak7-8
Maple6-7
Mahogany5-6
Pine3-4
Fir3-4
Spruce2-3

As you can see, hardwoods typically shrink and swell more than softwoods. This is something to keep in mind when choosing wood for a project. 

Temperature plays a part in wood shrinkage, but it is a lesser part than moisture.  Humidity levels (rising = expansion, and dropping = shrinkage) will determine movement in the wood.  However, cold temperatures can contribute to wood damage, too. 

Finally, the type of wood will determine, also, the extent of expansion and contraction.  

As Seinfeld’s George Costanza exclaimed, “Shrinkage is real.”

Last update on 2024-05-27 / Affiliate links / Images from Amazon Product Advertising API

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