400mm vs 600mm Centres SpacingComplete Guide
Everything you need to know about choosing between 400mm and 600mm centres spacing for wall studs, floor joists, ceiling joists, and roof rafters.
Quick Answer
Use 400mm centres spacing for load-bearing walls, most floor joists, and any application where maximum structural strength is required. Use 600mm centres spacing for non-load-bearing internal partition walls, some roof trusses, and situations where regulations allow it and you want to reduce material costs by up to 33%.
What Is Centres Spacing?
Centres (c/c) spacing is the distance measured from the centre of one framing member to the centre of the next. This is the standard way builders and Building Regulations specify the spacing of studs, joists, rafters, and trusses in timber-frame construction.
The two most common centres spacing measurements in residential construction are 400mm and 600mm. The choice between these two spacings affects structural capacity, material cost, insulation performance, and compatibility with standard building materials.
Standard building materials like 2400×1200mm plywood, OSB sheets, and plasterboard panels are manufactured in dimensions divisible by both 400 and 600mm, so panel edges always land on a framing member at either spacing.
400mm vs 600mm Centres: Side-by-Side Comparison
How the two most common framing spacings compare across every major application.
| Application | 400mm Centres | 600mm Centres |
|---|---|---|
| Exterior Load-Bearing Walls | Required by most designs for 89mm (38×89) stud walls. Strongest option. | Allowed with 140mm (38×140) studs in some designs (check structural engineer's specification). |
| Internal Non-Load-Bearing Walls | Common but not required. More fixing points for kitchen units. | Compliant with Building Regulations. Saves ~33% on stud material. |
| Floor Joists (47×225, typical span) | Spans up to ~4.9m with C16 graded timber. Stiffer floor. | Spans up to ~4.0m with same timber. May feel bouncy. |
| Ceiling Joists (non-loft storage) | Standard for loft storage. Supports plasterboard plus loads. | Adequate for plasterboard-only ceilings with no loft storage. |
| Roof Rafters / Trusses | Used in high snow-load areas (>1.0 kN/m² ground snow load). | Standard for engineered trusses in moderate climate zones. |
| Material Cost (per linear metre of wall) | ~£8–£12/m (more timber, more fixings). | ~£5–£8/m (fewer studs, less labour). |
| Insulation | Standard mineral wool batts for 89mm walls, full-fill for 140mm. | Wider bays allow better insulation performance. Better thermal bridging ratio. |
| Plasterboard Support | Excellent fixing. Less risk of nail pops and sagging. | Requires 15mm plasterboard on ceilings to prevent sag. |
When to Use 400mm Centres Spacing
400mm centres spacing is the more conservative and commonly used option. Here is when it is required or strongly recommended:
- Load-bearing exterior walls — Required by most structural designs for 89mm (38×89) wall assemblies carrying roof and floor loads.
- Floor joists for longer spans — 400mm centres allows joists to span greater distances. For a 47×225 C16 joist, 400mm centres spans up to 4.9m vs only 4.0m at 600mm centres.
- Areas supporting heavy finishes — Tile floors, stone worktops, or built-in cabinetry benefit from the extra support that 400mm centres framing provides.
- High wind or exposed zones — Building Regulations for exposed sites often mandate 400mm centres (or closer) for braced wall construction.
- Ceiling joists with loft storage — If the loft will be used for storage or future living space, 400mm centres provides the necessary load capacity.
- Walls with heavy cladding — Brick slips, render over sheathing, and fibre cement cladding all perform better with studs at 400mm centres.
Bottom line: when in doubt, 400mm centres is the safer choice. The extra material cost is modest compared to the structural benefits.
When to Use 600mm Centres Spacing
600mm centres spacing uses fewer framing members and can save significant material and labour costs. Here is when it is appropriate:
- Non-load-bearing internal partition walls — Building Regulations allow 600mm centres for internal walls that carry no structural load. This is the most common application.
- Engineered roof trusses — Most manufactured trusses are designed for 600mm centres spacing. The truss engineering accounts for the wider spacing.
- Advanced framing construction — Uses 140mm studs at 600mm centres with single top plates, reducing timber by up to 30% while improving insulation.
- Gable end walls — Non-structural gable end walls above the roof line can typically use 600mm centres spacing.
- Ceiling joists (plasterboard only) — Where the ceiling only supports plasterboard with no loft storage above, 600mm centres is compliant.
- Budget-conscious projects — On a 185 m² home, switching non-load-bearing walls to 600mm centres can save £600–£900 in timber alone.
Bottom line: 600mm centres is a smart choice where regulations allow it, especially for non-load-bearing walls and engineered trusses.
Building Regulations Requirements
UK Building Regulations and related standards provide specific guidance on when each spacing is permitted. Here are the key references:
- Approved Document A (Structure) — Sets out structural requirements for walls, floors, and roofs. Refers to BS 5268 / BS EN 1995 (Eurocode 5) for timber design.
- BS 5268-2 / BS EN 1995-1-1 — Timber design standards specifying allowable spans for joists, rafters, and studs at various spacings (400mm, 450mm, 600mm).
- TRADA span tables — Widely used in the UK to determine maximum joist and rafter spans for each timber grade, size, and spacing.
- Approved Document L (Conservation of fuel and power) — Impacts wall construction as thermal bridging through studs at 400mm centres is greater than at 600mm centres.
- BS 8103-3 — Structural design of low-rise buildings: timber. Covers stud wall requirements and spacing.
- Local authority building control may impose additional requirements. Always consult your local building control officer or approved inspector before finalising framing plans.
Important: Building Regulations are minimum standards. Your structural engineer or building control officer may require closer spacing based on site-specific conditions like soil type, wind exposure, or snow load.
Cost Comparison: 400mm vs 600mm Centres
Material savings is one of the biggest reasons builders consider 600mm centres spacing. Here is how the numbers break down:
For a standard 2.4-metre wall, 400mm centres spacing requires one stud every 400mm — roughly 2.5 studs per linear metre of wall. At 600mm centres, you need about 1.67 studs per linear metre. That is a 33% reduction in stud count.
On a typical 185 m² single-storey home with ~60 linear metres of internal partitions, switching from 400mm to 600mm centres saves approximately 50 studs. At £4–£6 per stud (2024 pricing for 38×89×2400 C16 timber from Jewson or Travis Perkins), that is £200–£300 in studs alone. Factor in reduced fixings, reduced labour (fewer studs to cut, carry, and nail), and the savings reach £600–£900.
However, do not use 600mm centres spacing just to save money on load-bearing walls. The cost of a structural failure or Building Regulations non-compliance far exceeds any material savings. The savings apply only where 600mm centres is compliant.
Impact on Other Materials
Your framing spacing does not just affect timber. It has a ripple effect across multiple building systems:
Insulation
Mineral wool batts come in widths designed for both 400mm and 600mm centres bays. At 400mm centres, standard batts are 370mm wide. At 600mm centres, batts are 570mm wide. The wider bays at 600mm centres actually improve thermal performance because there are fewer studs acting as thermal bridges. In advanced framing, 140mm studs at 600mm centres can achieve significantly better U-values with standard mineral wool batts.
Plasterboard
Standard 12.5mm plasterboard works well on walls at either 400mm or 600mm centres. However, on ceilings, 15mm plasterboard is required when joists or trusses are spaced at 600mm centres to prevent sagging. 15mm plasterboard costs about 20–30% more per board than 12.5mm, which partially offsets the framing savings.
Sheathing and Cladding
2400×1200mm plywood and OSB panels work at both spacings since their edges land on framing members. However, at 600mm centres, the panel spans a greater unsupported distance between studs. For structural sheathing (like wall bracing), verify the panel rating matches the stud spacing. Panels rated for 600mm centres are required when using 600mm spacing on structural sheathing applications.
Calculate Your Materials
Use our free calculators to get exact material quantities for your project at either 400mm or 600mm centres spacing: