RSJ vs I-Beam vs H-Beam – Full Comparison for Structural Projects

Understanding the differences between RSJ, I-Beam, and H-Beam steel sections is essential for optimal structural design. While all feature the characteristic “I” profile, each has distinct geometries, applications, and performance characteristics. This comprehensive guide compares these three section types to help you select the right steel for your 2026 construction project.

What Are the Differences?

RSJ (Rolled Steel Joist)

Characteristics:

• Traditional UK/British designation
• Narrow flanges relative to depth
• Tapered flanges (thicker at web, thinner at edges)
• Optimized for bending in one direction
• Typical designation: 203×133×25 (depth × width × kg/m)

Primary use: Beams (horizontal members supporting loads by bending)

I-Beam (American/International)

Characteristics:

• American terminology for similar sections
• Can have tapered OR parallel flanges
• Designation varies: W-shapes (wide flange), S-shapes (standard) in USA
• UK I-beams often synonymous with RSJ orUniversal Beams

Primary use: Beams and general structural applications

H-Beam (Heavy Beam / UC)

Characteristics:

• Heavier, stockier sections
• Flanges nearly as wide as depth (creating “H” profile)
• Parallel flanges
• Thicker web and flanges than equivalent-depth I/RSJ
• UK designation: UC (Universal Column) e.g., 254×254×73
• Also called “wide flange” or “W-shapes” in US terminology

Primary use: Columns (vertical members supporting axial loads) but also used as beams

Terminology Clarification

UK (2026):

• RSJ: Traditional term, now largely replaced by UB (Universal Beam)
• UB (Universal Beam): Modern designation for I-section beams with parallel flanges
• UC (Universal Column): H-section with wide flanges optimized for columns
• I-Beam: General term, can refer to RSJ or UB

USA:

• I-Beam: General term for all I-sections
• W-Shape: Wide flange beam (similar to UK UB/UC)
• S-Shape: Standard beam (similar to oldtraditional RSJ with tapered flanges)
• HP-Shape: Bearing pile sections

For this article:

• RSJ: Traditional tapered-flange sections OR general UK beams
• I-Beam: General term for I-profile sections
• H-Beam: Stocky sections with wide flanges (UK=UC)

Dimensional Comparison

Flange Width to Depth Ratio

Section Type	Width:Depth Ratio	Example
RSJ/Narrow I-Beam	0.4-0.6	203×133 (ratio 0.66)
Standard I-Beam/UB	0.5-0.7	254×146 (ratio 0.57)
H-Beam/UC	0.8-1.0	254×254 (ratio 1.0)

Visual profile:

• RSJ: Clearly taller than wide (“I” shape)
• I-Beam: Moderately wide (“I” shape)
• H-Beam: Nearly square profile (“H” shape)

Flange and Web Thickness

For similar weight:

Section Type	Flange Thickness	Web Thickness	Characteristics
RSJ	Thinner	Thinner	Efficient for bending
I-Beam	Medium	Medium	Balanced
H-Beam	Thicker	Thicker	Stocky, strong for compression

Which Section to Use When

RSJ/Narrow I-Beam

Best applications:

• Residential floor beams (short to medium spans <6m)
• Roof purlins
• Secondary structural members
• Where depth more critical than width
• Concealed installations (easier to box in)

Advantages:

• Efficient material use for bending
• Lighter weight for given strength
• Cheaper than wider sections
• Easy to conceal/box in

Limitations:

• Lower lateral-torsional buckling resistance
• Requires restraint from floor/roof members
• Not ideal for unrestrained beams

Typical UK sizes:

• 152×127×37
• 178×102×19
• 203×133×25, 203×133×30

I-Beam/Universal Beam (UB)

Best applications:

• Long-span beams (6-12m+)
• Heavy floor/roof loads
• Commercial/industrial structures
• Beams with limited lateral restraint
• Portal frame rafters

Advantages:

• Excellent bending capacity per kg
• Better lateral stability than narrow RSJ
• Wide range of sizes available
• Well-documented properties

Limitations:

• More expensive per meter than narrow RSJ (for lighter sections)
• Wider profile may complicate concealment
• Overkill for simple residential work

Typical UK sizes:

• 254×146×31, 254×146×37
• 305×165×40, 305×165×46
• 356×171×51, 356×171×67

H-Beam/Universal Column (UC)

Best applications:

• Vertical columns supporting multiple floors
• Short heavily-loaded beams
• Biaxial bending situations
• Transfer structures
• Portal frame columns
• Situations requiring maximum cross-sectional area

Advantages:

• Excellent compression resistance
• High lateral-torsional buckling resistance
• Similar strength in both axes (biaxial)
• Maximum bearing area for connections

Limitations:

• Heavier and more expensive than I/RSJ for same depth
• Inefficient when used purely as beam (unless short span)
• Larger footprint

Typical UK sizes:

• 152×152×30, 152×152×37
• 203×203×52, 203×203×60
• 254×254×73, 254×254×89

Structural Performance Comparison

For bending resistance (used as beam):

RSJ (depth 254mm, weight 31kg/m): Section modulus ~354 cm³
UB (depth 254mm, weight 37kg/m): Section modulus ~411 cm³  
UC (depth 254mm, weight 73kg/m): Section modulus ~777 cm³

Efficiency (section modulus per kg):

RSJ: 354/31 = 11.4 cm³/kg
UB: 411/37 = 11.1 cm³/kg (similar efficiency)
UC: 777/73 = 10.6 cm³/kg (less efficient for pure bending)

For compression resistance (used as column):

UC sections far more efficient due to:

• Higher radius of gyration
• Reduced slenderness
• Better buckling resistance

Cost Comparison (2026 UK Prices)

Per ton basis: RSJ/UB: £850-1,100/ton UC: £900-1,200/ton

Per meter for similar capacity:

Scenario: 5m span, 10 kN/m load

Section Type	Size	Cost/m	Total (5.3m)	Notes
RSJ	254×146×31	£75	£398	Adequate, efficient
UB	254×146×37	£88	£466	Better deflection control
UC	254×254×73	£165	£875	Massive overkill for this

Winner for beam applications: RSJ/UB (UC unnecessarily expensive)

Scenario: 3.5m column, 500 kN axial load

Section Type	Size	Cost/m	Total (3.5m)	Usability
RSJ	254×146×37	£88	£308	Marginal capacity
UB	254×146×43	£102	£357	Adequate but not optimal
UC	203×203×52	£115	£403	Proper capacity ✓

Winner for column applications: UC (purpose-designed)

Regional Variations

UK

Standard terminology:

• UB (Universal Beam) for I-beams
• UC (Universal Column) for H-beams
• “RSJ” still used colloquially but technically outdated

Availability: Excellent for UB/UC sizes

USA

Terminology:

• W-Shapes (W12×50 means ~12” depth, 50 lb/ft)
• Includes both I and H profiles
• HP (bearing pile) specifically for H-sections

Note: US sizes NOT interchangeable with UK without conversion

Europe (Poland, Germany, etc.)

Standard sections:

• IPE: Narrow I-beams (similar to UK narrow UB)
• HEA: Light H-beams
• HEB: Medium H-beams
• HEM: Heavy H-beams (similar to UK UC)

Example equivalents:

• IPE 270 ≈ 254×146×31 UB
• HEB 240 ≈ 254×254×73 UC

Selection Guide

Use RSJ/Narrow I-Beam when:

• Residential floor beams <6m span
• Fully restrained by floor joists/decking
• Budget constrained
• Easy concealment needed
• Standard residential loads

Use I-Beam/Universal Beam (UB) when:

• Commercial/industrial applications
• Long spans (>6m)
• Limited lateral restraint
• Heavy loads
• Portal frame rafters
• Modern construction standards require

Use H-Beam/Universal Column (UC) when:

• Vertical columns/posts
• Very short heavily-loaded beams
• Biaxial bending required
• Maximum lateral stability needed
• Load applied from multiple directions

Common Mistakes

Mistake 1: Using UC for standard beam application Problem: Paying for unnecessary weight and strength Example: Specifying 254×254×73 UC for 4m beam when 254×146×31 UB adequate Cost impact: £350 vs. £300 (+17% for no benefit)

Mistake 2: Using narrow RSJ for long unrestrained span Problem: Lateral-torsional buckling failure risk Example: 203×133×25 for 7m roof beam with occasional purlin restraint Solution: Use wider UB or provide intermediate lateral restraint

Mistake 3: Mixing terminology causing confusion Problem: Ordering “I-beam” without specifying actual size Result: Supplier sends generic section, may not match engineering spec

Solution: Always specify full designation (e.g., “254×146×37 Universal Beam to BS EN 10025 S275”)

Modern Trends

2026 UK market:

• “RSJ” terminology declining
• “UB” and “UC” standard in specifications
• Parallel flange sections now dominate (vs. historical tapered)
• Metric designations universal

Environmental:

• Increasing use of recycled steel
• Optimized sections reducing material waste
• Laser-cut custom sections for specialized applications

Conclusion

While RSJ, I-Beam, and H-Beam all feature I-shaped profiles, they serve different structural purposes:

RSJ/Narrow I-Beam: Economical beam choice for standard residential applications with good lateral restraint

I-Beam/Universal Beam: Optimal for most beam applications, especially longer spans and commercial work

H-Beam/Universal Column: Purpose-designed for columns and compression members, inefficient (expensive) if used purely as beam

Selection Priority:

1. Identify primary loading (bending vs. compression)
2. Check lateral restraint availability
3. Calculate required section properties
4. Select most economical section meeting requirements
5. Verify availability and lead time

For typical residential projects: UB (Universal Beam) offers best balance of performance, availability, and cost, though “RSJ” terminology persists in common usage.

Disclaimer: Section selection must be verified by a chartered structural engineer. This guide provides general comparison only and does not replace professional engineering design.