Does timber shrink in warmer weather?

From outdoor furniture to cladding, timber has long been one of the top choices for construction materials. It is durable, versatile and super sustainable, bringing plenty of green points to your build. But left untreated, you might also see shifts and movement in your timber over time. This typically occurs when the humidity levels change, but can it occur during temperature fluctuations as well? Our Ecochoice timber experts have the answers.

Can Timber Shrink in Hot Weather?

If you have noticed your timber shrinking in hot weather, you are not alone! Timber is known to both swell and shrink when the weather gets a little warmer, and with the heat waves in the UK over the past few years, some people are seeing their wooden products change a little in size.

This bizarre phenomenon actually has a very reasonable explanation behind it, all of which – of course – comes down to science.

Why Does Timber Shrink in Warm Weather?

Your timber is far from being 100% dry. View a board at its cellular level and you will find lots of water held between the fibres, most of which was absorbed while the tree was growing. But timber is also a hygroscopic building material, which means it takes on and lets go of water depending on surrounding humidity.

It is actually this fluctuation in moisture which is responsible for the swelling and shrinking of wood. The heat simply provides the cause of the moisture change.

To begin with, when water heats it expands. This can create that swelling of wood on hot days which causes doors to stick in their frames and sash windows to become harder to open and close. At the same time the heat can cause some of the water to evaporate from the wood (providing it has space to escape).

When the day becomes cooler and the water goes back to a more normal temperature, it shrinks again. This would return the timber back to its original size, but when the water loss is from evaporation, it can actually shrink further than before.

So, while it is not super likely you will see shrinkage in timber while it is still hot, as soon the weather begins to cool it is normal to see a slight loss of volume.

What Can You Do to Stop Timber Shrinkage?

If you do not like the sound of your timber swelling and shrinking, do not worry! There are ways you can maintain a more stable wood after construction. The first is by choosing a timber species which is more dimensionally stable, for example Oak, Western Red Cedar, and Iroko (there are plenty more from which to choose).

You can also treat your timber to prevent shrinkage. A water-resistant coating, for example, can prevent water loss and absorption to create a more stable timber product. You can also choose pre-modifed timber, such as OrganoWood or ThermoWood, for timber which is less likely to swell or shrink.

Find Out More at EcoChoice

At EcoChoice, we are experts in all things timber. If you have got a problem with timber shrinking and swelling as the weather changes, reach out to us and we will be happy to help. We can also recommend more suitable timber species options moving forward, helping you make the right choices for your timber construction.