Types of Timber
There are many different types of timber available, not only in terms of the type of tree it's sourced from, but also how it’s chemically treated and, following that, classed. Each type of timber is created with specific applications in mind - so choosing the right kind is vital in ensuring your timber is fit for purpose.
Contents
Intro
With so many different varieties and types of timber on the market, it can be difficult to decide what type of timber is best for the job at hand. Between hardwood and softwood, treated and untreated, graded and ungraded and different classes of timber to consider, it can easily become a little overwhelming. Use this guide to help break down the different types of timber you may come across and understand the applications each one is most apt to tackle.
Hardwood VS Softwood
When it comes to types of timber, the primary category is whether the timber is hardwood or softwood. Whether wood is hard or soft is dependent on what type of tree it’s been grown from; hardwoods are sourced from broad-leaved trees and typically grow slower and are thicker than softwoods. Let’s take a look at the differences between the two kinds of wood below:
Hardwoods grow slower and are thicker than softwoods, making them stronger, more fire-resistant and more durable due to their condensed and complex structure. Due to their slower growing time and required long drying times, hardwood is more expensive than its softwood counterpart, though hardwoods can be a good investment due to their longevity and resilience. Usually, softwoods have a shorter life than hardwoods and they often require more care and maintenance throughout their lifespan.
What is C16 Timber
C16 timber, much like C24, is a common way in which timber is graded. Generally, C16 is the most cost-effective option, ideal for use in smaller internal building jobs such as house extensions and joist work. This treated timber is the most widely available option, boasting strength, versatility and flexibility. However, this grade can sometimes possess aesthetic defects, like grain deviations and blemishes.
What is C24 Timber
C24 timber is a superior alternative to C16. The logs are felled in areas where a cold climate forces a slower growth rate. The result is a denser grain, providing excellent stability and a preferable cosmetic finish. You can use C24 in projects where aesthetics are integral, like in the construction of decking and balconies. Grade C24 timber comes in various lengths and widths, including the popular sizes; 4x2 treated timber and 6x2 treated timber.
What is PSE Timber
Let’s start with the basics: PSE timber stands for Planed Square Edge timber, but it’s also sometimes referred to as PAR (Planed All Round Timber). Simply put, this is a type of timber whose sides are smooth and the ends are only rough where they were cut to length. Typically, PSE timber is made using softwoods, such as Whitewood or Redwood.
PSE timber is an alternative option to rough sawn timber, whose name reflects the fact it was cut down using a saw, and no more processing occurred afterwards. Dealing with rough sawn timber may leave you vulnerable to splinters, but it also has its benefits; it’s ideal for jobs where the wood won’t be seen, or for fencing products such as posts. However, these days most Joist Timbers are regularised to ensure at least a semi-smooth finish and rounded corners.
Applications of PSE Timber
Thanks to the processing of PSE Timber, they make for a smart and smooth finish and are ideal for anywhere that the wood is visible, such as…
✅ Sash Windows
✅ Furniture
✅ Shelving
✅ Flooring
Classes of Timber
It is vital that the timber you choose is suitable for the project’s location, weather and environment. In order to ensure the correct timber is selected, both durability and use class play an important part in the decision process.
Durability Class
In order to easily identify the durability of any timber, each species is given a Durability Class. This shows you the life span of the wood and has to be considered relative to where the timber will be used (Use Class).
Class 5: Not durable. For example, Birch and Beech or any sapwood. Lifespan of 0-5 years.
Class 4: Slightly durable. For example, Scots Pine, Spruce. Lifespan of 5-10 years.
Class 3: Moderately durable. For example, Douglas Fir. Lifespan of 10-15 years.
Class 2: Durable. For example, Oak and Cedar. Lifespan of 15-25 years.
Class 1: Very Durable. For example, Teak, Greenheart and Jarrah. Lifespan of 25+ years.
If the timber is kept in a protected, internal environment, then the lifespan can actually be 50+ years, so the lifespan figures in the Class system refer to the lifespan in external, unprotected environments.
Use Class
The eventual end use of preservative-treated timber is classified into one of 5 categories (also known as Use Classes). These were established and defined in British EN standards BS-EN 355-1 and have been based on how at risk the timber would be from insect attacks and decay.
Use Class 1: Internal use which is kept dry permanently. For example, floor joists, floorboards or internal joinery. The main risk for this timber is insect damage as opposed to water damage. The level of risk of wood-boring insects attacking the timber depends on the geographical location and therefore can vary significantly.
Use Class 2: Internal use which is slightly at risk of becoming wet (ie. due to condensation). For example, framing for external walls. Attack by wood-destroying fungi is also a slight possibility.
Use Class 3 (coated): External use which is kept above ground and is coated. For example, cladding or window frames.
Use Class 3 (uncoated): External use which is kept above ground but uncoated. For example, fence rails.
Use Class 4: External use which has direct soil or water contact. For example, fence posts or decking which is sunk into the ground.
Use Class 5: External use which will be in regular or constant contact with the ground or water. For example, marine piling, sea defence, ships, dock gates.
What is Ungraded Timber
Ungraded timber is more prone to knots, splits and waney edges, compromising its strength. As a result, it is only suitable for non-structural work, though, thanks to its adaptability and affordability, is ideal for use in fencing and landscaping. Despite its more rugged looks, many people favour the natural twists and imperfections of ungraded timber as it can add a touch of character and charm to a garden.
Here’s a quick summary of the grades:
| Grade | Strength & Stability | Cost | Grain consistency & ‘neatness’ |
|---|---|---|---|
| C16 |  |
 |
 |
| C24 |  |
 |
|
| Ungraded |  |
 |
|
For further information regarding the legal standards surrounding the treatment of timber, please see the Timber Page provided by the NHBC (National House Building Council).
If you’d like more information on what applications treated timber is apt to tackle or what different kinds of timber are available, take a look through our other timber guide pages: