How to Check Structural Steelwork: A Homeowner's Guide to Beams and Supports

Removing a load-bearing wall to open up a kitchen-diner. Knocking through from the living room to the dining room. Adding a loft conversion with a ridge beam. If your project involves any of these, there's structural steelwork involved - and getting it right is non-negotiable.

Steel beams carry enormous loads. A typical domestic beam supporting a first floor and roof might be taking 10 to 15 tonnes - the weight of a couple of cars, concentrated on two small bearing points. If those bearing points aren't right, if the beam is the wrong size, or if it's been modified on site without engineering approval, you've got a problem that's expensive, disruptive, and potentially dangerous to fix.

Here's what to check, and when to check it.

TL;DR Checklist

• Beam size matches the structural engineer's specification (check the stamp/label)
• Bearing length at least 150mm at each support (or as specified)
• Padstones or engineering brick piers under each beam end - not standard bricks
• Beam is level and correctly positioned
• Acrow props still in place until mortar has fully cured (minimum 7 days)
• Structural engineer's calculations available on site
• Fire protection specified and applied where required
• Lintels above all openings - correct size, type, and orientation
• No cuts, holes, or welds not shown on the structural drawings

The Full Guide

Understanding what the steel does

Before diving into the checks, it helps to understand the job the steel is doing. When you remove a load-bearing wall, the loads it was carrying - floor joists, ceiling, roof, even walls above - need to go somewhere. The steel beam picks up those loads and transfers them sideways to the remaining supporting structure at each end.

This means three things matter equally: the beam itself (correct size and grade), the bearing points (where the beam sits), and the supporting structure below (what's carrying the beam ends). A failure in any one of these creates problems.

Checking the beam specification

Every structural steel beam has a serial size stamped or labelled on it - something like "254x102x28 UB" (Universal Beam). This tells you the depth, width, and weight per metre. It must match exactly what the structural engineer specified.

Ask to see the structural engineer's drawing and compare it to what's on site. The drawing should specify:

• Beam serial size and grade (typically S275 or S355 steel)
• Length including bearing lengths at each end
• Position - where exactly the beam sits in the structure
• Bearing details - what it sits on and how
• Any connection details - bolted, welded, or simply bearing

If the beam on site doesn't match the drawing - even slightly - don't proceed until the engineer has confirmed in writing that the substitution is acceptable. Builders sometimes swap beam sizes based on availability, and while a larger beam is usually fine, a lighter one may not be.

Bearing length and padstones

The bearing length is how far the beam sits on its support at each end. This is typically a minimum of 150mm, but your structural engineer may specify more for heavier beams or weaker supporting walls.

This matters because the entire load the beam is carrying gets concentrated at these two points. If the bearing length is too short, the beam end can slip or the supporting wall can be overloaded at that point.

Padstones are critical. A padstone is a block of dense material - usually a precast concrete pad or a stack of engineering bricks - placed under each beam end. Its job is to spread the concentrated load from the beam over a wider area of wall.

Standard bricks have a compressive strength of about 20-30 N/mm2. Engineering bricks are 70 N/mm2 or more. A dense concrete padstone is higher still. Using standard bricks as a bearing for a structural beam is one of the most common defects found in domestic construction - and one of the most serious. Standard bricks can crush under the concentrated load, causing the beam end to settle and everything above it to crack.

Temporary propping

When a load-bearing wall is removed and a beam installed, temporary acrow props support the structure while the permanent bearing arrangement cures. These props carry the full structural load until the mortar around the beam ends and padstones has reached adequate strength.

Removing props too early is a surprisingly common problem. The builder wants to clear the site, the props are in the way, and "the mortar looks set." But mortar takes time to gain full strength - a minimum of 7 days at normal temperatures, longer in cold or damp conditions.

If props are removed before the mortar has cured, the beam can settle under load. Even a few millimetres of settlement can crack the brickwork above and around the beam. This is difficult and expensive to repair.

Fire protection

Steel loses its structural strength rapidly when heated. At 550 degrees C - which a house fire can reach within minutes - steel retains only about 60% of its room-temperature strength. This is why fire protection is sometimes required.

In domestic properties, the requirements depend on what the beam is separating:

• Within a single dwelling (e.g., an open-plan kitchen-diner): fire protection is often not required, though building control will confirm
• Between dwellings (e.g., a flat conversion): fire protection is mandatory, typically 30 or 60 minutes
• Between a house and integral garage: fire protection is required (30 minutes minimum)

Fire protection is usually either intumescent paint (a special coating that swells when heated, insulating the steel) or fire-rated plasterboard boxing around the beam. Both must be applied before the beam is covered by other construction.

Lintels above openings

Every opening in a wall - windows, doors, service hatches, meter boxes - needs a lintel to support the masonry above it. Lintels are essentially smaller versions of beams, and the same principles apply: correct size for the span, adequate bearing at each end, and the right type for the application.

Common lintel types in domestic construction:

• Steel lintels (e.g., Catnic, IG): most common, available in standard lengths for standard openings
• Concrete lintels: used where fire resistance is needed or for heavier loads
• Combination lintels: steel with insulation to reduce cold bridging

Check that lintels are the right way up (they have a specific orientation - installing them upside down reduces their capacity), that they extend at least 150mm past each side of the opening, and that the correct type has been used (cavity lintels for cavity walls, single-leaf lintels for internal walls).

Common Problems

Insufficient bearing length. The beam only sits 100mm on the wall instead of the specified 150mm. This happens when the opening is cut slightly too wide or the beam is slightly too long for the available space. It's a structural compromise that must be addressed by the engineer.

No padstones. Beam ends sitting directly on standard bricks. The bricks may look fine initially, but over months and years the concentrated load crushes them gradually. By the time you see cracking in the wall above, the damage is done. Always check for padstones before the beam ends are covered.

Props removed too early. The builder removes the acrow props after two or three days because "the mortar's gone off." It hasn't. Mortar reaches functional strength at about 7 days and continues gaining strength for weeks. Premature prop removal causes settlement, cracking, and potentially structural distress.

Wrong beam substituted. The specified beam isn't in stock, so the builder uses what's available - often a lighter section. This might look the same to the untrained eye but may not have adequate capacity for the loads. Any substitution must be approved in writing by the structural engineer.

Questions to Ask Your Builder

1. "Can you show me the structural engineer's drawing for this beam?" - It should be on site and readily available. If it's not, that's a red flag.

2. "What are the padstones made of?" - The answer should be concrete or engineering bricks. If they say "bricks" without the "engineering" qualifier, check what's actually been used.

3. "When are you planning to remove the props?" - The answer should be at least 7 days after the mortar was laid, longer in cold weather. If they say "tomorrow," push back.

4. "Does building control need to see this before it's covered up?" - The answer is almost certainly yes. Structural steelwork is a notifiable inspection stage. Confirm the inspection is booked.

5. "Is any fire protection needed on this beam?" - Your builder should know the answer and it should match what building control has specified. If they're not sure, ask building control directly.