What size steel beam do I need? A plain guide for Norfolk homeowners

Opening up a kitchen and dining room, removing a chimney breast or adding a rear extension often means taking out part of a wall that holds the house up. In its place goes a steel beam, often called an RSJ. One of the first questions we hear is: "What size beam do I need?"

The honest answer is that we can't tell you, and neither can anyone else without doing the calculations. This guide explains why, and what you'll need to sort out before ordering.

Why there's no simple answer

A beam's size depends on far more than the width of the opening. A structural engineer will look at things like:

• The span: how far the beam has to stretch between supports.
• What sits above it: floors, walls, roof, water tanks, and even the weight of people and furniture.
• How the loads arrive: whether it's carrying a wall evenly along its length or concentrated loads from joists or posts.
• The supports at each end: what the beam bears onto, and whether padstones or extra posts are needed to spread the load.
• Deflection: a beam can be strong enough not to fail but still bend enough to crack plaster above. Engineers design to limit this.
• Fire protection and connections: how the beam is protected and joined to other steel or masonry.

Two openings the same width in two different houses can need very different beams. That's why online sizing tables and rules of thumb aren't a safe substitute.

You need a structural engineer

For any structural alteration, a qualified structural engineer should calculate and specify the beam. They'll give you a set of calculations and usually a drawing showing the section size, length, bearings and any padstones or connections.

Building Control will normally want to see these calculations before approving the work, so it pays to get them done early. If the wall is shared with a neighbour, you may also need to think about the Party Wall Act.

What the engineer's spec will tell you

A typical spec will name the type of steel section (for example a universal beam or universal column), its serial size and weight, the length including bearings, and any extras such as end plates or bolted connections. It may also say how the beam should be protected against fire and corrosion.

Once you have that, ordering is simple.

Ordering your beam

With your engineer's spec in hand, you or your builder can order the exact section, cut to length, from our Order Steel page. You can choose raw or red oxide primed, collect free from our Rackheath workshop or have it delivered within 15 miles. Stock sizes are usually ready in 2 to 3 working days, and special-order sizes in 3 to 4.

If the beam needs plates, holes or welded connections, we can fabricate those to the engineer's details too.

A few practical tips

• Check the length allows for the bearing at each end, not just the clear opening.
• Think about access: how will a long, heavy beam get into the house?
• Make sure your builder plans temporary support (props) for the wall while the beam goes in.

If you have your calculations and want to check what to order, give us a call on 01603 560808 or WhatsApp a photo of the spec to 07824 656634. We're happy to help.