Treated UC4 C24 Timber Decking Joist is a high-strength, structural-grade softwood timber that has been heavily pressure-treated to Use Class 4 (UC4) standards, allowing it to be used in direct contact with the ground or in permanent freshwater contact.

• Subframe & Joist Support: Used as the primary structural framework and joists underneath raised or ground-level garden decking platforms to support the deck boards safely.

• Ground-Contact Landscaping: Ideal for structural timber projects that touch the earth, such as retaining walls, raised bed framing, edging, and landscape steps.

• Sub-Surface Construction: Employed in heavy-duty outdoor civil and landscaping applications where timbers are buried or subjected to high moisture levels.

• Bridge & Walkway Framing: Used for constructing the structural support beams for outdoor boardwalks, jetties, and pedestrian footbridges over wet terrain or streams.

• Outbuilding & Shed Foundations: Serves as robust bearers and floor joists for timber sheds, garden offices, and outdoor summerhouses resting close to the ground.

Available for collection from our Rugby branch or local delivery using our own fleet.

Delivery is kerbside and the final offloading position is always subject to safe access and the driver’s discretion.

Please tell us before delivery about:

• Narrow roads or restricted entrances
• Parked vehicles or limited turning space
• Overhead cables, trees or other obstructions
• Soft, sloping or unsuitable ground
• Any other access concerns

Enter your postcode on the product page to check your delivery area. We’ll confirm the delivery date after your order is placed.

What does "UC4" (Use Class 4) mean?

UC4 is a British/European standard for timber treatment that means the wood has been heavily pressure-treated with preservatives to withstand prolonged or permanent contact with the ground or fresh water. It provides maximum protection against rot, decay, and insect attack.

Can UC4 joists touch the ground directly?

Yes. Unlike standard UC3 treated timber (which is only rated for above-ground use), UC4 joists are specifically rated to be laid directly on or embedded into soil, gravel, or concrete without prematurely rotting.

Do I need to treat cut ends or drill holes?

Yes. Whenever you cut, notch, or drill a UC4 joist, you expose the untreated inner wood. You should brush a compatible end-grain wood preservative onto all fresh cuts to maintain the timber's rot resistance.

How far apart should decking joists be spaced?

For standard domestic decking, joists are typically spaced between 400mm and 450mm apart (centre-to-centre). If you are building a commercial deck or expect heavy loads, you may want to reduce this spacing to 300mm for extra rigidity.

How should I anchor or fix UC4 joists to the ground or concrete?

Depending on your build, you can use post-mix concrete with post-support brackets, adjustable paving support pedestals, or heavy-duty masonry anchors if fixing directly to an existing concrete patio or foundation slab.