Most people call any steel beam an RSJ, short for rolled steel joist. Strictly, an RSJ is an older type of beam with tapered flanges. Almost every beam fitted in UK houses and buildings today is a universal beam, written UB, rolled to BS 4-1 with parallel flanges.
How a beam size is written
A size such as 203 x 133 x 25 UB gives the depth of the section in millimetres, then the width of the flange, then the mass in kilograms per metre. So a 203 x 133 x 25 UB is about 203 mm deep, 133 mm wide and weighs about 25 kg for every metre of length.
Other common sections
- Universal columns (UC): almost square, used as posts and for heavier loads in a shallow depth.
- Parallel flange channels (PFC): a C shape, often used where a beam sits against a wall or as stair stringers.
- Hollow sections (SHS, RHS and CHS): square, rectangular and round tubes, used for posts, frames and balustrades.
- Flat plates and angles: used for connections, bearing plates and edge trims.
Why the section must not be changed
Your structural engineer chooses the section for the load, the span, the deflection limit and the fire protection. A beam that looks similar can be much weaker, so we fabricate exactly the section on the approved drawing. If a different size would be easier to source or fit, we ask the engineer first.
Send us the engineer’s drawings and we return a free, itemised quotation within 48 hours.
