A Clear Guide to Durability Classes of Wood + Chart

You’ve probably come across Durability Class 1 or 2 when looking for wood for your projects. But what does this wood’s durability class tell us and how many durability classes of wood are there?

The durability class, in a nutshell, indicates how long a specific type of wood will last. Wood in durability class 1 is extremely long-lasting, whereas wood in durability class 5 is not at all. Then there are classes two through four, which are located in the center of Class 1 and class 5.

What does the durability of wood mean for your next woodworking project, and why are wood durability classes so important? Continue reading to learn more.

What is wood durability

The wood durability class indicates how long a specific type of wood can be expected to last. To determine a wood’s durability class, the heartwood is exposed to bacteria and fungi or mold. Like this, it has been investigated which types of wood can and cannot withstand this.

As a result, it implies something about the lifespan of wood. High durability wood has a long lifespan and is frequently of high quality. Wood durability classes indicate whether the wood is appropriate for the job at hand.

This way, you’ll know you don’t have to build something in the neighborhood of water or in moisture areas with wood with a durability class of 5.

why is durability in wood important

When it comes to wood, there is no such thing as a good or bad type of wood. If the right wood is chosen for the right conditions, each type of wood will do what it’s supposed to do.

However, if you use wood from a specific durability class for a project that the wood is not suitable for, your project will be short-lived.

If you have an outdoor project that calls for wood from durability classes 1 to 3, and you use wood from durability class 5, you will be able to start over in a matter of years.

Before you start your project, think about what you’ll be doing with the wood and how the wood will be affected by the environment. That is why understanding the durability classes of wood is critical.

Another advantage of being knowledgeable about the durability classes of wood is that it saves money. If you want to build a drywall structure, it would be a waste of money to use expensive wood with a durability class 1 that will never be exposed to the elements.

By accurately estimating which wood of which durability class you require for your project, you can achieve the maximum in terms of age and quality at the lowest possible cost.

Heartwood vs sapwood

To understand the sustainability of wood, it is necessary to distinguish between heartwood and sapwood.

Sapwood is the outer, living part of a trunk or branch, whereas heartwood is the inner, or dead part of a trunk or branch, accounting for the majority of the trunk’s cross-section. The color of the heartwood and sapwood can usually be distinguished.

Looking at a cross section of the wood, you can see that heartwood is darker than sapwood, as shown in the image. Sapwood is soft, and as a result, sapwood of all types is classified as grade 5, which means it is not durable.

A young tree has only sapwood, but as it ages, the center of the tree dies to heartwood. When wood dies, a chemical is released that causes the wood to change color, making it stronger and more resistant to insect attack.

This is critical for the tree because heartwood provides structural support for the tree while sapwood transports sap around the tree.

The ratio of heartwood to sapwood is determined by the number of leaves on a tree and its rate of growth. More leaves and faster growth necessitate more water, which necessitates a greater amount of sapwood.

What durability classes of wood are there?

Durability classes of wood are graded on a scale of 1 to 5. Outdoor projects are best suited to wood types in classes 1–3. The wood durability classes 4 and 5 are classes for indoor uses.

Durability classes	Lifespan	Wood species	Uses
Durability class 1	25 years or longer	Ipé, Mukulungu, Massaranduba, Azobé, Accoya, Padouk.	On/in the water: Decks, fences, facade cladding, furniture wood, jetty, and sheet piling.
Durability class 2	15 – 25 years	Bankirai, Kapur, Thermally Modified Pine/Spruce, Purpleheart, Chestnut, Oak, Western Red Cedar, Garapa, Robinia.	Decking, fences, facade cladding, furniture wood, fencing and pergolas.
Durability class 3	10 – 15 years	Keruing, Larch, Thermally modified bamboo, Tigerwood, Impregnated spruce/pine, Douglas wood.	Decks, fences, canopies, fencing, pergolas and facade cladding.
Durability class 4	5 – 10 years	Untreated pine and spruce wood.	Not for outdoor applications. Floors, construction wood
Durability class 5	5 years	Birch, Beechwood, Poplar.	Not for outdoor applications, but for furniture or plywood.

Durability Class 1

When it comes to wood types in durability class 1, think of high-quality woods like Ipé and Padouk. These woods have a long lifespan and can be used in a variety of applications where direct ground contact is not a problem.

When used outdoors, these types of wood have a life expectancy of 25 years or more. The lifespan of wood products is often even longer if they are properly assembled and maintained.

Durability class 2

Hardwoods, such as the popular Bankirai, are frequently used in wood projects And have a durability class of two. This category also includes wood species such as Oak and thermally modified Spruce and Pine.

These woods are still very durable, albeit of lower quality, and have a lifespan of about 20 years. They frequently work a little harder, are less resistant to moisture, and absorb a little more dirt than durability class 1 wood types. This, however, is reflected in the price.

Durability class 3

Many treated softwoods are classified as having a durability class of three. There are also hardwoods such as Keruing, which is considered the inferior version of Bankirai, and thermally modified bamboo. These wood products are generally less expensive than wood with higher durability classes, but this is reflected in quality, function, and lifespan.

Durability class 3 wood species have a lifespan of about 15 years. However, you can also make very attractive wooden projects such as decking or fences here. These types of wood are an excellent choice for the budget-conscious customer.

Durability class 4

When untreated spruce and pine are used in projects, they fall under durability class 4. Because of the lack of durability treatment, these wood species have a lifespan of approximately 5 to 10 years.

Due to this low durability, it is not recommended to use these kinds of wood outdoors.

Durability class 5

The types of wood that fall under durability class 5 have a lifespan of barely 5 years. Due to their medium to low hardness and density, these types of wood are sensitive to rot, fungi and insects.

Wood species with durability class five are, for example, poplar, birch, but also beech wood. Never use these types of wood outdoors.

What can increase the durability of wood?

Wood species have a durability class, which can be increased by certain treatments. Untreated pine and spruce wood, for example, are not suitable for outdoor use, whereas impregnated pine or spruce can be used for a variety of outdoor applications.

This can be seen in decking or fence screens, for example. The advantage of these impregnated woods is that they are inexpensive and have a long lifespan. The disadvantage is that these types of wood have been chemically treated, which is not the most environmentally friendly solution.

Another method of treatment to make wood last longer is thermal modification. Woods such as Spruce and Pine are often thermally modified. For this, the wood is heated with steam, resulting that this type of wood that normally has durability class 5 is suddenly just as durable as high-quality hardwood.

In addition, these types of wood have relatively little effect after the thermal modification process, such as shrinkage and warping. They also weigh less than untreated wood. That is why this type of wood is very suitable as facade cladding.

The biggest advantage of this type of treatment is that is is very environmentally friendly because for this process only heat and water are used. However, there is also a disadvantage to thermally modified wood, and that is that it is quite fragile, which means that it can be damaged quite quickly. That is why it is not recommended to use this type of wood for flooring.

In addition, you can of course also treat the wood with a wood finish such as stain, paint, or oil to extend its life. Check whether these materials are suitable for the type of wood you are going to use.