C24 Treated Joists: The Strongest Choice for Framing & Flooring

 


When building a structure that needs long-term strength and reliability, not all timber is equal. C24 treated joists stand out as the premium choice for builders who refuse to compromise on quality.

In this guide, you’ll learn:
✔ Why C24 joists outperform standard C16 timber
✔ Key advantages of pressure-treated C24 for durability
✔ Best applications (flooring, roofing, decking frames)
✔ How to choose the right size for your project

By the end, you’ll understand why professionals consistently choose C24 treated joists—and where to source the best ones.

What Are C24 Treated Joists?

C24 timber is a high-strength graded softwood, treated with preservatives to resist rot, insects, and moisture damage. Compared to standard C16 timber:

FeatureC24 JoistsC16 Joists
Bending StrengthHigher load capacityStandard strength
Moisture ResistancePressure-treated for outdoor useOften untreated
Typical UsesHeavy-duty flooring, long spansLight framing

Why "Treated" Matters

The pressure treatment forces preservatives deep into the wood fibers, providing:
✔ 5-10x longer lifespan vs. untreated timber
✔ Protection against wood-boring insects
✔ Reduced warping/splitting in humid conditions

Top 5 Reasons to Use C24 Treated Joists

1. Unmatched Strength for Heavy Loads

C24’s higher density and fewer knots allow it to:

  • Support greater floor loads (ideal for commercial spaces)

  • Span longer distances without sagging (up to 5m with 195x45mm joists)

2. Built to Last in Harsh Conditions

Unlike untreated timber, C24 joists:
✔ Resist fungal decay (even in damp subfloors)
✔ Repel common wood pests (deathwatch beetle, termites)
✔ Withstand UK weather extremes when used outdoors

3. Precision-Graded for Consistency

Every C24 joist is machine-graded to ensure:

  • Uniform strength (no weak spots)

  • Straighter edges (easier installation)

  • Reliable load ratings (BS 5268-2 compliant)

4. Cost-Effective Long-Term

While 10-15% pricier than C16, C24:

  • Reduces callbacks (no rot-related repairs)

  • Extends structure lifespan (20+ years vs. 10-15 for C16)

5. Versatile for Multiple Applications

  • Flooring systems (suspended, solid, mezzanine)

  • Roofing rafters (especially for heavy tiles)

  • Decking frames (outdoor durability)

  • Wall framing (high-wind resistance)

C24 Joists vs. Alternatives: Which Should You Use?

MaterialBest ForLifespanCost
C24 TreatedHeavy loads, outdoor use20-30 yrs££
C16 UntreatedIndoor framing only10-15 yrs£
Engineered I-JoistsUltra-long spans25+ yrs£££
Steel BeamsIndustrial projects50+ yrs££££

Key Takeaway:

  • C24 is the sweet spot for residential & commercial projects needing strength + affordability.

How to Choose the Right C24 Joist Size

For Flooring (Domestic)

  • Span ≤ 3m → 145x45mm

  • Span 3-4m → 170x45mm

  • Span 4-5m → 195x45mm

For Roofing (Pitched)

  • Standard roofs → 145x47mm @ 400mm spacing

  • Snow load areas → 195x47mm @ 600mm spacing

Pro Tip:
Always consult BS 5268-2 span tables or use W Hanson’s joist calculator.

Where to Buy Quality C24 Treated Joists

Not all suppliers meet UK grading standards. At W Hanson, we provide:
✔ PEFC-certified sustainable timber
✔ Pre-cut lengths (2400mm–4800mm)
✔ Trade discounts on bulk orders

Why Builders Trust Us:
✅ 30+ years supplying UK construction
✅ Stock held nationwide for fast delivery
✅ Technical support for complex projects

Final Advice: Don’t Risk Substandard Joists

C24 treated joists are the backbone of durable structures. Remember:
✔ Always specify treated for outdoor/exposed areas
✔ Use correct spacing (400-600mm centers)
✔ Seal cut ends with preservative

Need C24 joists ASAP? Order now for nationwide delivery.

FAQs

Q: Can C24 joists be used for ground contact?
A: Yes, if UC4 treated (ask for "ground contact grade").

Q: How long do treated joists last outdoors?
A: 20-30 years if properly installed/maintained.

Q: Are C24 joists stronger than engineered wood?
A: No, but they’re more cost-effective for mid-range spans.

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