Oak… Is it really better? IMPORTANT
You may be surprised by this. Read on…
British Standard EN350 defines the durability of commonly available wood species. In 2016, this guidance was updated in light of new test data. This is important for landscaping contractors and consumers of landscaping services.
Quite simply, this is a question of ‘How durable is the timber?’ …. ‘Will it last? … ‘Is it good enough for landscaping?’.
Answering these questions depends on if the timber is in contact with the ground, where they are more exposed to biological degradation. In which case, the use class must be Class 4. To be classed as this, the timber must have a durability rating of 2 or better to achieve a 15 year service life (with reference to BS8417:1011).
Here’s the problem. Whilst Oak heartwood does have a durability rating of 2… the sapwood does not. Also, different batches of Oak are grown in different conditions and during different environmental cycles. This also influences how durable they are! Not all Oak is as ‘good’.
This introduces another British Standard, against which landscaping contractors may be held accountable… BS8605-1:2014. This states that for species with a variable durability rating, the lowest durability class within the range should be assumed. In the case of Oak, not all Oak can be described as durable with a 15yr+ service life.
In fact, some Oak can only be described as “slightly durable” with a 5-10 year service life! In which case, UC4 treated softwoods are more durable and also cheaper!
Equally, if you do choose to use the cheaper softwood sleepers… It is vitally important to ensure that they are indeed UC4 treated. Not all are. So, choose a supplier carefully and ask the right questions to get the assurances and evidence you need… otherwise, materials may not be fit for purpose.
So, in summary:
Avoid using untreated timber, including Oak.
Apply protective treatments, such as oil based wood preservative and end grain treatments.
Verify the supply chain to ensure service life meets expectations
Design for durability… e.g. installing on at least 50mm of shingle rather than soil, and incorporate water drainage and ventilation.
Maintain… apply preservative every few years, inspect annually and replace decaying sections before total structural failure occurs.
If you are a past client and have any concerns for the condition of your timber sleepers, please do not hesitate to contact us.
Full credit and thanks for the contents of this blog post go to Karl Harrison (Landscaping Expert Ltd and the Association of Professional Landscapers; February 2025)
