Treated Carcassing Timber

What we supply

• C16 graded carcassingThe everyday structural grade for joists, rafters and studs.
• C24 graded carcassingStronger grade for longer spans or smaller sections.
• Treated timberPressure treated for protection against rot and insect attack.
• Wall plate and nogginsSmaller sections for plates, noggins and bracing.
• Longer lengthsLengths beyond the common range to order.
• Fencing and sleeper timberTreated posts, rails and sleepers on request.

Sizes and specifications

Strength classes	C16, C24 (BS EN 338)
Common sections	47 × 75 mm to 75 × 225 mm
Common lengths	2.4 m to 4.8 m in 300 mm steps
Treatment	Use class 2 or 3 to BS 8417

Sizes and standards are typical for the UK market; exact figures depend on the manufacturer and are confirmed on your quote.

Common uses

• Floor joists
• Roof rafters and ceiling joists
• Stud walls
• Decking frames

Choosing carcassing timber

C16 or C24?

C24 is stronger and stiffer, so it can span further or use a smaller section. Span tables and your structural drawings decide which grade and size you need.

Which treatment?

Treatment is specified by use class. Timber inside a building is usually use class 1 or 2; external timber out of ground contact is use class 3; timber in ground contact needs use class 4.

Cut ends

Treat any cut ends with a suitable end-grain preservative, especially on external work.

Building regulations differ across the UK. In England, building work is checked against the Approved Documents, for example Part A for structure and Part L for energy efficiency, through your council's building control team or a registered building control approver. Wales has its own Approved Documents, including its own Part L for energy efficiency, and building control is handled by the local authority or a registered approver. In Scotland most building work needs a building warrant from the local authority, assessed against the Building Standards Technical Handbooks. In Northern Ireland building work follows the Building Regulations (Northern Ireland), with guidance in the Technical Booklets, and applications go to the council's building control team.

How it arrives on site

Timber is delivered in packs or bundles on a flatbed; long lengths need clear access along the drop point. We agree the drop point and offload method when we price your order. Read more about how delivery works.

How much do you need?

A floor 4.2 m wide with joists spanning 3.3 m at 400 mm centres needs 12 joists, plus trimmers and noggins. The section and grade, such as 47 × 200 mm C24, come from span tables or your engineer; send us the timber schedule and we will price it.

Treated Carcassing Timber: questions

What does C16 and C24 mean?

They are strength classes under BS EN 338. C24 timber is stronger and stiffer than C16, which lets it span further for the same size.

Is your carcassing timber treated?

We supply treated carcassing as standard for structural work. Tell us if the timber is for external or ground-contact use so we supply the right treatment level.

What sizes of joist do I need?

That depends on the span, spacing, loading and grade. Use span tables or your engineer's design; building control will check.

What lengths are available?

Common lengths run from 2.4 m to 4.8 m in 300 mm steps, with longer lengths to order.

Can you cut timber to length?

Ask when you request a price; we will tell you what cutting is possible for your order.

Why is my treated timber green or brown?

The colour comes from the preservative. It fades over time and does not tell you how well the timber is protected; the use class does.