Does wood expand when cold? Interestingly…

Like metals, wood can expand or contract. There are two parts in wood: the sapwood and the heartwood. Each contain fibres that can hold water. The heartwood is the “dead” part of wood and doesn’t hold water. On the other hand, the sapwood is the part of wood that contains 72% of the wood total moisture content.

Only real wood can expand or contract.

But to what extent? Does it expand in the cold? Or only during summers. When does wood expand in the winter? Can you stop wood from expanding? Does wood expand in the rain? How can you stop the door in your home from expanding? We’ll answer these questions and more in this article.

So, read to the end to find out what we think about wood expansion, what makes wood expand, and how to stop wood from expanding.


What makes wood expand?

Wood expands when it has been exposed to moisture. Sometimes, wood can expand because of heat.


Can wood expand in the cold?

Yes, wood can expand in the cold. Even in colder temperatures. However, wood can shrink in the cold too, which may cause cracks inside the wood.

The reason why wood can expand or shrink in the cold isn’t because of the temperature. Rather it’s because of its internal humidity level. The humidity level of wood is the amount of water in the wood. If there’s more water in the wood in the cold, it will likely expand. If there isn’t, the wood will shrink or contract.



At what temperature does wood expand?

Wood expands at all temperature. Whether it’s really cold or mildly hot, wood can expand or contract. Although temperature affects how wood expand, it isn’t the main reason for the expansion. The real cause is the humidity level of the wood or the amount of water in the wood. It is the actual reason for the contracting and expanding of the wood. The degree of the surrounding temperature will determine how much water is lost through heat in the wood during low humidity. Or how much water is gained during high humidity.


Does water shrink or expand in the cold?

Yes, wood can shrink or expand in the cold.


To what direction does wood expand?

Because of its grain structure, wood expands in three different directions.

First, wood can expand longitudinally, parallel to the grain. Along this direction, wood is fairly stable since it loses less moisture and shrinks less (around 0.01%)

Second, wood can expand across the grain, tangent to the growth rings. Actually, wood moves more across the grain and can lose up to 8% of its moisture when the surrounding environment is dry, causing it to shrink more.

Lastly, wood can expand radially or horizontally, away from the pith along the radius of the growth rings. Along this line, wood can shrink up to 4%. It is why wood sawed (quartersawn) radially are generally more stable and offer long term performance. They are less likely to crack than woods sawn parallel to the grain direction and tangent to the growth ring (plain-sawn). Plain-sawn woods are susceptible to surface cracks and pre-mature decay.


When does wood expand during winter?

Wood expands in the winter when the relative humidity or amount of water in the air is high. However, it is unlikely that wood, especially the ones outdoor, will expand in the winter since humidity levels are usually low at the time of the year.

But the wood in your home may expand in the winter. This could be as a result of high humidity in your home. Of course this shouldn’t be, since dry air often comes with the winter.

But if you notice the wood inside your house is expanding, it may be due to high internal humidity levels. Most times, this problem may be as a result of water leaks, condensation problems and poor ventilation. To prevent wood from expanding in your house, you can get a powerful dehumidifier. This should easily bring down the humidity level in your house.

Also, try checking for condensation around your window area. If you find enough moisture, replace the windows immediately. Check also your roofs, plumbing fixtures, and eaves for leaks and fix them immediately. Also, check for leaks in your windows and doors and fix them, too.


To which way does wood expand?

Wood can expand either longitudinally, radially (horizontally) or across the grain (tangent to the growth ring).


Does heat make wood expand too?

Yes, heat can make wood expand. Usually, this depends on the environment’s humidity. An increase in temperature (more heat), raises the humidity of a place. As such, the air contains more water vapour which is absorbed by the wood (the volume of water expands as temperature rises). As the heat or temperature rises, the water in the air increases, the wood absorbs more moisture (water vapour), making the wood expand more.


Does wood expand with humidity?

Yes, wood expands with humidity. In fact, the relative humidity surrounding the wood has a bigger impact on how it expands and how much moisture it can hold than temperature.


Do wooden floors expand in the summer?

Yes, your wood floor may expand in the summer. However, suppose you live in regions that experience dry summers (with low air moisture) like in deserts or places closer to deserts, your wood floor may likely shrink since there is little or no moisture in the air. If this isn’t the case and you live in an area that enjoys high moisture content in the air during summers, expect your wood floor to expand.


What is the best moisture level for wood?

The best or ideal or most acceptable moisture level for wood is 6 to 8% for indoor wood applications, while it’s 9 to 14% for exterior wood. The best moisture level or moisture content for depends on: the wood’s final use and the average relative humidity of the environment where the wood will be used.



What is the ideal humidity level for wood?

The ideal or most acceptable humidity level for wood is between 35% to 55%. Higher than 55% will cause the wood to expand too much due to high moisture content absorbed from the surrounding environment. Though there’s a limit to the amount of moisture any wood can absorb. Generally, moisture content will never reach 50%.


Does wood expand in the rain?

Yes, wood expands in the rain. Living wood or lumber (part of a tree) contains cells that hold water. When the wood is cut and milled, those cells slowly dry up or shrink. If this same wood is exposed to rain, the cells reabsorb rainwater and swell again, making the wood expand. They shrink or contract again during dry seasons.

But rain isn’t good for wood, particularly for those that lack natural oils. Natural oils in wood help prevent the growth of microorganisms that thrive under wet conditions.

Woods that are most vulnerable to rot caused by rain are those found outdoors, especially applications that have joints. Water can collect in these joints, helping microorganisms to thrive. The best way to prevent rot in wood is to apply paints or wood finishes regularly.


How to stop wooden door from expanding during cold or winter

You have a internal wooden door that expands in the winter and won’t shut when you try to close it. What can it be treated with to prevent the expansion?

Naturally, wood expands or contracts (this applies to only real wood). Often this depends on the relative humidity of environment with the wood. Woodworkers often construct doors with this in mind. But then, your wood may expand more than it should if the humidity level in your house is higher than the one outside.

Normally, during winters, the air is usually dry (there’s less moisture in the air). As a result, you shouldn’t experience any internal wooden expansion. But since you do, it’s because the moisture content in the air in your house is high. This is often caused by water leaks, condensation problems and poor ventilation.

You can stop or prevent the door from expanding or contracting by sealing it. This will work if the wood is sealed airtight with some sort of epoxy resin. Doing this reduces the amount of moisture the door can absorb. For a more effective result, seal the entire door and paint it with an oil paint, including around the door’s edges (top and bottom).

If you prefer your door bare (without paint), remove the door next winter and shave off the holes or exposed areas.


Other ways to deal with wood expansion during cold or winter

  • You can disassemble important furniture before winter.
  • Always go for high quality hardwood with high stability and strong resistance to environmental changes for your home or outdoor furniture.
  • Don’t expose your furniture for too long in the cold.
  • Alternatively, you use laminate wood for your furniture. Laminate wood won’t expand!