C16 Loft Joists Sizing Reference Guide (UK)
Timber grades, section sizes and questions for professional review. No allowable span values are provided; consult official sources and a qualified designer.
Verify against TRADA Eurocode 5 span tables
Numeric span values for loft joists in the UK must be confirmed against the latest TRADA published Eurocode 5 (BS EN 1995-1-1) span tables, NHBC Standards Chapter 6.4, and a structural engineer's calculations. Building Control approval is required for new structural work — under Part A of the Building Regulations in England & Wales, Section 1 of the Scottish Technical Handbook in Scotland, or Part D in Northern Ireland. This page is a planning starting point, not a substitute for design sign-off.
About C16 Softwood
A grade label alone does not establish suitability. Confirm the actual product, grading evidence and intended use with a qualified designer.
Common species: European Whitewood (Spruce-Pine-Fir), British Sitka Spruce.
About loft joists as a structural member
Loft joists span between supports in a loft conversion or floored loft, carrying domestic floor live load (1.5 kN/m² to BS EN 1991-1-1). Heavier loading than ceiling joists — sized using floor joist tables.
Common C16 loft joist sizes used in the UK
Section sizes most commonly stocked and specified for C16 loft joists at UK builders' merchants. Maximum allowable spans for each section must be confirmed against TRADA Eurocode 5 span tables.
| Section size (mm) | Typical spacing (mm) | Max single span (m) |
|---|---|---|
| 47×100 | 400 | verify against TRADA Eurocode 5 table |
| 47×100 | 600 | verify against TRADA Eurocode 5 table |
| 47×150 | 400 | verify against TRADA Eurocode 5 table |
| 47×150 | 600 | verify against TRADA Eurocode 5 table |
| 47×195 | 400 | verify against TRADA Eurocode 5 table |
| 47×195 | 600 | verify against TRADA Eurocode 5 table |
| 47×220 | 400 | verify against TRADA Eurocode 5 table |
| 47×220 | 600 | verify against TRADA Eurocode 5 table |
| 47×250 | 400 | verify against TRADA Eurocode 5 table |
| 47×250 | 600 | verify against TRADA Eurocode 5 table |
- 47×100
- Typical spacing (mm)
- 400
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 47×100
- Typical spacing (mm)
- 600
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 47×150
- Typical spacing (mm)
- 400
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 47×150
- Typical spacing (mm)
- 600
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 47×195
- Typical spacing (mm)
- 400
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 47×195
- Typical spacing (mm)
- 600
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 47×220
- Typical spacing (mm)
- 400
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 47×220
- Typical spacing (mm)
- 600
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 47×250
- Typical spacing (mm)
- 400
- Max single span (m)
- verify against TRADA Eurocode 5 table
- 47×250
- Typical spacing (mm)
- 600
- Max single span (m)
- verify against TRADA Eurocode 5 table
Sizing guidance and UK Building Regulations notes
Project-specific sizing guidance is withheld pending qualified review. Ask a qualified designer to assess loads, supports, connections, exposure and the applicable current standard. No size, spacing or span on this reference page is an approved specification.
How to read a C16 loft joist span table (UK)
- Determine your required span — the clear distance between supports.
- Note your spacing — typically 400 or 600 mm centres.
- Identify your loading category (BS EN 1991-1-1 for floors, BS EN 1991-1-3 for snow, BS EN 1991-1-4 for wind).
- Look up the TRADA Eurocode 5 loft joist table for C16 and read off the smallest section whose span exceeds your required span. Confirm with a structural engineer's calculation.
UK timber standards behind C16 sizing
Strength classes for European softwoods are defined in BS EN 338 (Structural timber — Strength classes), with design rules in Eurocode 5 (BS EN 1995-1-1). The legacy UK code BS 5268-2 is still referenced in older tables but Eurocode 5 has been the active design code since 2010. For new-build housing, NHBC Standards Chapter 6.4 (Timber and joinery) sets the practical specification baseline accepted by NHBC, Premier Guarantee and other UK structural warranty providers.