Types of Steel Beams in UK Construction: UB, UC, RSJ and Beyond
When specifying structural steel in the UK, the term RSJ (Rolled Steel Joist) is still widely used on site, but in most modern projects it refers to either a Universal Beam (UB) or a Universal Column (UC). These are the two most common types of steel beams used in UK construction — and while they look similar, they have different proportions and are specified for different structural roles.
This guide covers the main types of steel beams you'll encounter on a UK project — UB, UC, RSJ, PFC and CHS — what each is, how they're typically used, and how to avoid ordering the wrong section. Section selection is always confirmed by a qualified structural engineer.
For general availability across both section types, see: View RSJ Steel Beams.
Types of Steel Beams Used in UK Construction
UK structural steelwork uses a small number of standard rolled section types. The four you'll see most often on residential, commercial and light industrial projects:
- Universal Beam (UB) — I-shaped section, deeper than it is wide. The standard horizontal load-bearing section. Used for floor beams, roof support, and structural openings.
- Universal Column (UC) — I-shaped section with near-equal depth and width. Designed for vertical compressive loads. Used for columns, posts and mezzanine supports.
- Parallel Flange Channel (PFC) — C-shaped section with parallel flanges. Used for trimmer beams, edge beams, and where a flat back face is needed against a wall.
- Circular Hollow Section (CHS) — tubular round section. Used for columns and architectural exposed steelwork where appearance matters or where torsional resistance is required.
Builders, engineers and suppliers often use "RSJ" as a catch-all term for any of these — particularly UB and UC. The correct supply terminology is the proper section name (UB, UC, PFC, CHS) from the structural engineer's drawings. The rest of this guide explains UB and UC in detail, with brief notes on PFC and CHS at the end.
For dimensions, weights and span guidance across all section types, see the RSJ steel beam size guide.
What Is a Universal Beam (UB)?
A Universal Beam (UB) is a rolled steel I-section that is deeper than it is wide. This shape means it is commonly specified where the steel member is primarily working in bending rather than compression.
Typical applications include:
- Horizontal support for internal load-bearing walls
- Floor support members and joists
- Structural lintels for extensions and refurbishments
- Steel members spanning between supports, subject to structural design
Although many builders still refer to these as "RSJs", the correct supply term is Universal Beam. Common UB sizes range from 127 × 76 × 13 UB up to 356 × 171 × 51 UB for typical residential and light commercial work, with larger sections specified for heavier loads or longer spans.
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What Is a Universal Column (UC)?
A Universal Column (UC) is also a rolled steel I-section, but its depth and flange width are much closer in proportion, giving it a more square appearance compared with a UB. This near-square geometry makes UCs efficient at resisting axial compression — they're the right choice when the section needs to carry vertical loads.
Universal columns are commonly specified for:
- Vertical load paths
- Steel columns and posts
- Applications dominated by compressive forces
- Situations where stability in both axes is typically specified
- Mezzanine columns and steel-framed buildings
Despite the name, a UC is defined by its geometry rather than the orientation in which it is installed. Common UC sizes range from 152 × 152 × 23 UC up to 254 × 254 × 73 UC for typical residential and commercial work.
👉 Explore Universal Columns (UC)
Universal Beam vs Universal Column: Key Differences
| Feature | Universal Beam (UB) | Universal Column (UC) |
|---|---|---|
| Section proportions | Deeper than wide | Near square |
| Typical orientation | Horizontal members | Vertical or multi-directional |
| Primary load type | Bending loads | Axial / compressive loads |
| Common site term | Often called RSJ | Often called RSJ |
| Visual appearance | Taller web, narrower flange | Wider flange, shorter web |
| Common use | Floors, roofs, openings | Columns, posts, supports |
| Specification basis | Structural engineer | Structural engineer |
All dimensions are nominal and subject to standard mill tolerances. The correct choice between UB and UC is always determined by structural calculations, not appearance or availability.
Why UBs and UCs Are Commonly Mixed Up
On UK building sites, "RSJ" is often used as a catch-all term for structural steel. This frequently leads to:
- Universal columns being requested when a universal beam is shown on drawings
- Orders being placed based on names rather than section proportions
- Incorrect price comparisons between different section types
In practice, the structural engineer's drawings or beam schedule will clearly state whether a UB or UC is required, along with the nominal size and steel grade.
Other Steel Section Types: PFC and CHS
UB and UC cover most residential and commercial steelwork, but two other section types appear regularly enough on UK drawings that it's worth knowing what they are.
PFC — Parallel Flange Channel
PFC steel means Parallel Flange Channel — a C-shaped section with two parallel flanges connected by a vertical web. Where a UB has an I-shaped profile with flanges on both sides of the web, a PFC has flanges on one side only, giving it a flat back face. This makes PFCs useful for trimmer beams in floor openings, edge beams along masonry walls, and any application where a flat back surface against a wall or upstand is required. PFCs are supplied to BS EN 10365 like UBs and UCs, in the same S355 structural grade.
CHS — Circular Hollow Section
CHS means Circular Hollow Section — a tubular round steel section. CHS is used where its appearance is part of the architectural design (exposed columns in commercial and residential projects), where torsional resistance is needed, or where the round profile suits the application better than an I-section. CHS columns are common in modern residential extensions with exposed steel and in light industrial structures.
For both PFC and CHS, the structural engineer's drawings will specify the exact section. Both can be supplied alongside UB and UC orders.
Practical Ordering Considerations
Before ordering steelwork, it is common to confirm:
- Whether the section is specified as a UB, UC, PFC or CHS
- The nominal depth × width shown on drawings
- The steel grade noted by the engineer (S355 is the standard UK structural grade)
- The required finish — mill finish or red oxide primed (see the red oxide RSJ guide for the difference)
- Delivery length and any cutting requirements
Clear terminology at enquiry stage helps suppliers quote accurately and reduces unnecessary revisions.
Frequently Asked Questions
What are the main types of steel beams used in UK construction?
The four most common rolled section types are Universal Beam (UB), Universal Column (UC), Parallel Flange Channel (PFC) and Circular Hollow Section (CHS). UBs and UCs cover most residential and commercial structural work; PFCs are used for trimmer and edge beams; CHS is used for tubular columns and architecturally exposed steelwork.
Is a Universal Beam the same as an RSJ?
RSJ is a legacy term meaning Rolled Steel Joist. In modern UK construction, what builders call an RSJ is typically either a Universal Beam (UB) or a Universal Column (UC). UBs are by far the most common.
What is the difference between a Universal Beam and a Universal Column?
A Universal Beam is deeper than it is wide and designed for bending loads — typically used horizontally to span floors, roofs and structural openings. A Universal Column is near-square in profile and designed for axial compressive loads — typically used vertically as a column or post. Both are I-section rolled steel, but the proportions and intended load direction differ.
Can a Universal Column be installed horizontally?
Yes. A UC can be installed in different orientations if specified by a structural engineer. The name describes the section's geometry, not the orientation in which it must be used.
What is PFC steel?
PFC means Parallel Flange Channel — a C-shaped rolled steel section with two parallel flanges and a flat back face. PFCs are used for trimmer beams, edge beams along walls, and any application where a flat-backed steel section is required. Supplied to BS EN 10365 in S355 grade.
How do I know which section is required for my project?
The structural engineer's drawings or beam schedule will specify whether a UB, UC, PFC or CHS is required, along with the nominal size, length and steel grade. Do not substitute one section type for another without engineer approval — even where dimensions appear similar, the section properties differ.
Are UBs and UCs interchangeable?
No. Even where dimensions appear similar, section properties differ — UBs are optimised for bending, UCs for compression. Substitutions should not be made without approval from a qualified structural engineer.
Structural Disclaimer
Universal beams, universal columns, PFCs, CHS and all other structural steel sections must be specified by a qualified structural engineer. Installation and use are subject to approved designs and building control approval. This article is provided for general guidance only and does not replace professional structural design.
Ordering Steel Sections
Once your structural engineer has confirmed the section type, nominal size, length and finish, steel sections can be ordered for delivery across mainland UK. All beams supplied in S355 grade to BS EN 10025-2 unless otherwise specified.
👉 View RSJ Steel Beams
👉 Explore Universal Beams (UB)
👉 Explore Universal Columns (UC)