RSJ or universal beam: what the terms actually mean
Ask three people on a Dublin site what steel is going in and you will hear RSJ, UB, UC and joist used as if they are the same thing. They are related but not identical, and the difference matters when you are reading a quote or a drawing.
RSJ is an old name that stuck
RSJ stands for rolled steel joist, a section with tapered flanges that was the standard beam for decades. Very little new construction uses a true RSJ today, but the name survived and is now used loosely for any structural beam in a house.
If someone tells you the job needs an RSJ, they almost certainly mean a universal beam. The distinction only becomes important when you are matching new steel to an old beam in a period property, where a genuine tapered flange RSJ may still be in place.
Universal beams and universal columns
A universal beam, written as UB, has a deep web and narrower flanges. It is efficient at spanning horizontally, which is why it is the normal choice over a wide rear opening. Sizes are written as depth by width by weight per metre, so a 203x133x25 UB is 203mm deep, 133mm wide and 25kg per metre.
A universal column, written as UC, is squarer in proportion and designed to carry load vertically. UCs do appear horizontally in houses, usually where headroom is tight and the engineer needs a shallower section that is still strong enough, or where a post is carrying a beam above.
Why the section size is not negotiable
Homeowners sometimes ask whether a smaller or cheaper section would do. The honest answer is that we cannot make that call and neither can your builder. The engineer sizes the steel against deflection limits as well as strength, because a beam that does not break can still sag enough to crack the plaster above it.
If the specified section genuinely will not work, for example because it is too deep for the ceiling line you want, the route is to go back to the engineer and ask for an alternative design. They can often achieve the same opening with a different arrangement.
What we need to price it
Give us the section size, the length, the connection details and the finish and we can price immediately. A photograph of the relevant page of the engineer's drawing is enough to start.
We fabricate all of these sections in house, including drilling, cleats and end plates, and deliver across Dublin and Leinster ready to install.
Want this priced for your own job? Send us your drawings or a photo and we will come back with a fixed price, usually within one working day.
Common questions
Need this done properly? Talk to the workshop.
Send us drawings, a sketch or a site photo. We come back with a fixed price and a firm lead time, usually within one working day.