Wood facts: Key knowledge for specifying durable timber for outdoor use

When choosing a timber for outdoor applications, the more you know the better. Knowledge helps you separate unsuitable species from the right picks, and lays the groundwork for a long-lasting timber product which is fit for purpose. The good news? We have the facts you need to get started.

Learn more about how to find the right timber species for your outdoor project with these pointers.

Hardwoods Are not Always Hard

Thinking that all hardwoods are going to be super tough is, unfortunately, a mistake. While there are many durable, strong hardwood species out there, you can also find hardwoods which are on the softer side, e.g. Balsa, or that are not suitable for outdoor use. On the other hand, softwood timbers can sometimes be really tough. Western Red Cedar and Larch, for instance, are two softwoods that are very durable and perform well in many outdoor applications.

The moral of the story? Do not judge all timber species by whether they are labelled hardwood or softwood.

Not All Durable Timbers Can be in Ground contact

While there are plenty of durable timber species you can choose for outdoor use, not all of them are suitable for the same applications. In particular, you need to know the difference between outdoor use and ground contact use. When building decking, for instance, any timber which comes into contact with the ground needs to be extremely durable, with excellent resistance to rot.

A great example here is Oak. While we love using untreated Oak for many outdoor applications, it is not always best-suited for long-term ground contact. Ipe and Ekki, on the other hand, will withstand ground contact with ease.

Outdoor Projects Need Use Class 3–5 Timber

Following on from the previous point, one of the easiest mistakes to make when choosing timber for outdoor use is ignoring Use Classes. These classifications exist for a reason: they tell you exactly how much moisture exposure a piece of timber can handle before things start going wrong.

Use Class 3 is going to be your baseline for outdoor above-ground applications, such as cladding, decking or benches. Move into areas where timber sits on or very close to the ground, and you are firmly into Use Class 4 territory, and if you are building something which will be permanently in contact with water, you will need Use Class 5.

Moisture Movement Can Make or Break Your Project

Different timber species handle moisture in very different ways, and this matters a lot outdoors. Some timbers stay super stable as humidity and weather conditions change, while others expand and contract if they take on (or release) too much moisture too quickly. This is particularly important if you are choosing a timber species for cladding or decking, where movement can cause gaps.

Species such as Cedar and Iroko are naturally dimensionally stable, making them ideal choices. Other timbers may still be durable, but need careful maintenance and installation to keep movement under control.

Timber Can Lose its Colour Outdoors

No matter how tough a timber species is, sunlight will always win the colour battle eventually. UV exposure breaks down the timber’s surface fibres, causing even the richest, most vibrant timbers to fade to a silvery grey over time.

Some people love that weathered look, while others prefer to maintain the original colour of their timber. If you fall into the latter group, you will need to apply a suitable UV-protective treatment to prevent fading.

Remember, though, that fading is not a flaw, and it is definitely not a sign that your outdoor timber is damaged.

Speak to Our Experts

There is a lot to consider when choosing a timber species for outdoor use. Feeling a bit overwhelmed? We’ve got you. Our timber experts at EcoChoice would be happy to talk more about your options and find the right timber species for your project.

Get in touch today.