Understanding UC4 Treated Products
When choosing timber products for your home or garden, it is essential to pick the right timber for the job. When working on external or outdoor projects, it is important to make sure the correct level of treatment and preservation has been used to ensure a prolonged life.
All timber is split into 5 use class categories and determines the correct end use of timber.
What does ‘UC’ mean?
The Use Class system is a British standard classification of wood treatments that has a treatment criteria that timber must meet for various purposes. The higher the use class, the more at risk the timber is to decay and infestation therefore a stronger treatment is required to protect the wood.
What are the different levels of treated timber?
The Use Class system is split into 5 main categories:
- UC1 - wood that is used indoors with no water contact.
- UC2 - wood that is used indoors with occasional water contact.
- UC3 - wood that is used outdoors, above ground and exposed to the weather e.g. fencing panels.
- UC4 - wood that is used outdoors, in permanent contact with the ground e.g. fence posts.
- UC5 - wood that is regularly in contact with water, e.g. boats.
For timber in ground contact, it is essential that the timber has been pressure treated to achieve UC4 standard. To do so, the timber goes through a more vigorous and penetrative process.
To Achieve UC4
The treatment process uses chemicals that have anti-insect and anti-fungal properties that penetrate deep into the wood, resulting in a highly durable and water resistant timber.
In order to attain UC4 standard, it is important that the timber is dried to the correct moisture content prior to chemical penetration. It is first kiln dried, reducing the moisture content of the wood to a maximum of 28%, ensuring the timber is at the optimum saturation level so the correct amount of chemicals can get into the timber.
The kiln dried timber is then ready to be treated via an airtight vessel. The chemical is added to the chamber where a vacuum is applied to force the preservative chemical into the timber. Once the timber has reached the correct amount of penetration, the vacuum is released and the excess preservative is pumped out.
The treated wood is then air dried for 48 hours, resulting in long-lasting water resistant timber, which should give at least 15 years service life for ground contact timber.
Use Class 4 (UC4)
Timber that is used in direct contact, or very close contact with the ground or fresh water must be Use Class 4.
Suitable end uses for UC4 timber include:
- Garden fencing (for example, fence posts)
- Agricultural timbers
- Retaining walls
- Playground equipment
- Decking stump posts
- Joists and sub-structures
Incised Use Class 4 (UC4)
Incised UC4 products have the same suitable applications as UC4. However the timber is penetrated even deeper than standard UC4, where a technique called mechanical incising is used.
This process involves holes being created on all 4 sides of the timber, allowing the treatment to permeate throughout, leading to a longer desired service life. Incised UC4 timbers offer as a minimum, a 15-year UK warranty, allowing complete peace of mind.
