When choosing timber for a building, landscaping or DIY project, one of the most important decisions is whether to use treated or untreated timber.
Both have their place, but using the wrong type can affect the lifespan and performance of your project. At MSS Timber Merchants, we believe choosing timber should start with understanding where it will be used and the conditions it will face.
Here’s what you need to know.
What Is Treated Timber?
Treated timber has undergone a preservation process designed to improve its resistance to decay, fungi and wood-destroying insects.
This makes it particularly useful in situations where timber is likely to be exposed to moisture, changing weather conditions or other environments where untreated wood could deteriorate more quickly.
Treatment requirements vary depending on how and where the timber will be used, so it's important to choose timber suitable for the intended application.
When Is Treated Timber Necessary?
Treated timber is generally the preferred choice for outdoor and exposed applications, particularly where there is an increased risk of moisture or decay.
Common uses include:
- Fencing and fence posts
- Garden structures
- Decking substructures
- Landscaping projects
- External structural timber
- Sheds and outbuildings
- Timber exposed to the weather
- Applications involving ground contact, where appropriately treated timber is required
Not all treated timber is designed for the same conditions. Timber that will be used above ground, for example, may have different treatment requirements from timber that will be in direct contact with the ground.
Always check that the treatment specification is appropriate for the intended end use.
Where Can Untreated Timber Be Used?
Untreated timber can be an excellent choice when the wood will remain dry and protected from the elements.
It is commonly suitable for internal applications such as:
- Interior joinery
- Shelving
- Furniture
- Internal studwork, where appropriate
- Decorative timber projects
- Internal carpentry
- General indoor DIY projects
Because untreated timber hasn't undergone a preservative treatment process, it can also be preferable when a natural finish is required.
The key consideration is exposure. If untreated timber is repeatedly exposed to moisture without suitable protection, its service life can be significantly reduced.
How Long Does Treated Timber Last?
There's no single lifespan that applies to every piece of treated timber.
Its longevity depends on several factors, including the type and quality of treatment, intended use, installation, local environment, moisture exposure and ongoing maintenance.
Correctly specified treated timber can provide a considerably longer service life in exposed environments than equivalent untreated timber.
However, treatment shouldn't be viewed as making timber indestructible. Good design and installation remain important. Preventing unnecessary water retention, providing appropriate drainage and following recommended maintenance practices can all help maximise its lifespan.
What About Untreated Timber?
Untreated timber can last for many years when it is kept indoors and protected from excessive moisture.
Problems are more likely to occur when untreated timber is used outside without adequate protection. Regular exposure to rain and damp conditions can encourage fungal decay and cause movement, splitting or other deterioration.
While paints, stains and exterior wood finishes can provide additional surface protection, applying a coating isn't necessarily equivalent to using timber that has been appropriately preservative-treated for a demanding application.
Important Considerations for Outdoor Timber Projects
If you're planning an outdoor project, don't choose timber based on appearance or price alone.
Think about where the timber will sit, whether it will touch the ground, how often it will become wet and how easily it can dry afterwards.
Good outdoor timber design should also minimise areas where water can collect. Appropriate fixings, ventilation and drainage can make a substantial difference to the long-term performance of the project.
Cutting treated timber can also expose untreated material inside the wood. Where required by the timber or treatment manufacturer's guidance, cut ends and drilled areas should be treated with an appropriate end-grain preservative.
Treated or Untreated: Which Should You Choose?
A simple rule of thumb is:
For dry, protected indoor projects, untreated timber may be perfectly suitable. For external or moisture-prone applications, correctly specified treated timber is often the better choice.
The exact specification matters, however. A fence post in direct ground contact faces very different conditions from internal timber in a dry room, so the timber should always be selected for its intended end use.
Get the Right Timber for the Job
Choosing the correct timber at the start of a project can save time, money and unnecessary replacement work later.
At MSS Timber Merchants, we supply timber for a wide variety of trade, construction, landscaping and DIY applications. If you're unsure whether you need treated or untreated timber, speak to our team about your project and we'll help you identify a suitable option.
Need timber for your next project? Contact MSS Timber Merchants and get the right materials for the job.
