Whether you’re building an extension, removing a wall, taking on a loft conversion, or working on a larger commercial project, choosing the right steel section matters. The problem? Most people get handed a structural drawing full of letters, RSJ, UB, UC, PFC, and have no idea what they mean.
So, here’s a clear, no-nonsense breakdown of the most common steel sections you’ll see in UK construction, what they’re used for, and why they matter.
At Phoenix Steel, we supply all of these sections cut to size for projects across the North East, but first, let’s make sense of the terminology.
1. RSJ (Rolled Steel Joist)
“RSJ” is the everyday term people use, but in modern structural engineering, it usually refers to a Universal Beam (UB).
What an Universal Beam (RSJ) is used for:
- Supporting open-plan knock-throughs
- Carrying load-bearing walls
- Loft conversions
- Rear and side extensions
- Steel Frames
Key features:
- Strong vertical load capacity
- Wide web and narrow flanges
- Ideal for spans supporting floors, roofs and walls
If your builder says, “You’ll need an RSJ for that wall,” this is usually what they mean (Universal Beam).
2. UB (Universal Beam)
A Universal Beam is one of the most common structural steel sections in UK building.
Shape:
“I-beam” shape (narrow flanges with a wider central web)
Best for:
- Beams carrying heavy loads
- Long spans
- Extensions and structural alterations
Why engineers choose them:
They handle vertical loads incredibly well while keeping weight down. They’re the go-to for most residential and commercial beams.
3. UC (Universal Column)
A Universal Column looks similar to a UB, but the proportions are different.
Shape:
Almost square profile – flanges and web are similar dimensions.
Used for:
- Vertical columns
- Support posts
- Frames
- Situations needing strong compression strength
Why pick a UC instead of a UB:
It’s designed to take heavy vertical loads without buckling. If your design includes steel posts, you’re probably looking at a UC.
4. PFC (Parallel Flange Channel)
(Often called C-channel or C-section or U Section)
A Parallel Flange Channel forms a “C” shape.
Used for:
- Supporting floor joists
- Edge protection
- Smaller spans and lighter loads
Why it’s popular:
PFCs can be used as lintels or combined to create box beams. They’re handy in house builds where you don’t need the full weight of a UB.
5. Angle (L-Section)
As the name suggests, angles are an L-shaped steel section.
Used for:
- Window lintels
- Door Lintel
- Trims and frames
- Brackets
- Secondary supports
- Shelving, gates, fencing
- Light fabrication work
Why they’re useful:
Angles are lightweight but strong and can reinforce frameworks or create rigid edges. They’re used everywhere – from construction sites to small fabrications.
6. SHS, RHS & CHS (Box & Circular Sections)
These are hollow sections, ideal for structural and aesthetic applications.
SHS (Square Hollow Section)
Even sides – good for columns, balustrades, frames.
RHS (Rectangular Hollow Section)
Longer on one side – ideal for lintels, frameworks, supports.
CHS (Circular Hollow Section)
Strong in all directions – great for handrails, posts, and architectural features.
Used for:
- Structural frames
- Gate and fence fabrication
- Balconies and railings
- Mezzanine floors
- Architectural features
Why people choose hollow sections:
They’re clean-looking, versatile, and incredibly strong for their weight.
How Do You Know Which Section You Need?
Simple answer: your structural engineer specifies it.
But even then, it’s helpful to understand the notation.
A UB might be listed as:
203 x 133 x 25 UB
Which means:
- 203mm depth
- 133mm width
- 25kg per metre
*Universal sizes will differ depending on kgs per metre
We can cut all sections to length and prepare them exactly as shown on your drawings – including holes, plates etc
Choosing the Right Supplier Matters
Steel isn’t a “buy it anywhere” material. You want reliability, correct cuts, accurate fabrication, and fast delivery. Learn more about what to look for in a steel supplier
At Phoenix Steel, we supply:
- Structural beams (RSJ, UB, UC, PFC)
- Box section, angle and flats
- Cut-to-length steel
- Same-day collection and fast delivery across the North East
Whether you’re doing a home renovation or managing a full commercial build, we’ll make sure you get the right steel, on time, with no drama.
Need Steel for Your Next Project?
If you need a beam, a quote, or advice based on your drawings, you can reach us directly at Phoenix Steel. We’re always happy to help – whether it’s a simple lintel or a full structural frame.